Posts Tagged ‘Structural Systems’

OMHC Approval of ABS (Pier) Pads

May 10, 2011

On April 20, 2011, the Ohio Manufactured Homes Commission (OMHC) held a hearing on proposed changes to Ohio Rule 4781, which governs installation of manufactured homes in Ohio.  One change to those rules was to allow ABS pads as footings for  manufactured homes.  The exact wording is as follows:

“ABS footing pads shall be permitted if used in accordance with the manufacturer installation instructions and/or specification sheet of the specific ABS pad being used.  The use of ABS pads must be used in conjunction with solid perimeter skirting in accordance with paragraphs (D) (1) to (D) (4) and (E)(1) to (E)(6) of rule 4781-6-02.5 of the Administrative Code.”

We attended this hearing specifically to voice concerns about this revision to the previous rules that did not allow these pads.  Three ABS pad manufacturers, Oliver, Polyvulc, and Tie-Down Engineering, also spoke at the hearing in favor of the changed rules.  Our assessment of the attitude of the OMHC during the hearing was that it favored the rule change.  Therefore, we wrote the letter attached to this blog post and submitted it to the OMHC within the comment period (less than 24 hours).  That letter is included here:

OMHC Has Approved ABS Pads For Manufactured Homes

We found later that the OMHC had indeed passed the rule change, allowing ABS pads.

As the letter states, we are concerned that ABS pads will be used in conditions where they are not intended.  Although the rule change states that the installer must follow the manufacturer’s installation instructions, we had reviewed the instructions of the three main pad manufacturers and found them greatly lacking in detail, and where there is a lack of detail, there is opportunity for misuse.  In a conversation with two of the manufacturer’s representatives after the hearing, we were informed that other states that have allowed ABS pads also have training sessions particularly for ABS pads.  Our feeling is that if ABS pads are allowed, they need to have such required training additional to following the manufacturer’s instructions.

Essentially, our concern is that ABS pads require that soil be used as a replacement for concrete footings or slab.  Granted, some soils can be “hard as concrete” when at certain moisture content and without organic matter and voids.  That is to say, the soil has the same bearing capacity as concrete.  However, unlike concrete, which has a bearing capacity that changes little over a wide range of conditions, the bearing capacity of soil can change dramatically.

Therefore, if soil is going to be used to replace concrete, the soil conditions must be controlled.  In the one decently documented case where ABS pads were successfully used, soil moisture and frost heave were well-controlled.  In this case, insulated skirting to maintain temperatures above freezing in the crawlspace and drainage around the home’s perimeter were used.  The manufacturers’ installation instructions usually state a minimum required  soil bearing capacity and that the pads be placed “at or below the frost-line”.  The insulated skirting, moves the frost line to grade.  The required soil bearing capacity is in part essentially a requirement for proper drainage because the soil bearing capacity can drop significantly as the soil moisture increases.  Thus, soil moisture needs to be controlled through proper drainage.

But, can installers be trusted to measure soil bearing capacity accurately or to accurately calculate whether an ABS pad be able to take the weight put on it?  Can most inspectors be trusted to check the right parameters and review the required information.  The OMHC has left those questions wide open.  Currently, installers and inspectors are not required to have special training.  Therefore, no two installers will be doing the same installation or checking the same parameters.  That is why we wrote the letter to the OMHC.  If ABS pads are going to be used, they need to be used properly and uniformly.  They cannot simply be used in place of concrete footings because soil is not exactly the same as concrete and the weight being put on the soil will usually be more for ABS pads than for concrete footings.

We are going to continue pursuing the issues of proper training for ABS pad use.  We are also aiming for the requirement that a licensed engineer approve the use of ABS pads to assure that homeowners get the home that they believe they are buying.  In a future blog, we plan on commenting research sponsored by the Ohio Manufactured Home Association which has been used to back the approval of the pads.  Stay tuned.

Advertisements

Want Proof That Termites Are (Misplaced) Evil?

April 15, 2011

I recently had a structural inspection that showed (once again) how much damage a gang of termites can do to a home. This damage was located in the rim joists and sole plates of a home with brick veneer. However, these termites had incentive to invade the wood due to the rim joists and sole plates being apparently exposed to excess water coming from behind the brick veneer.

Some background is needed before getting into the termite business. The sole plates are the boards that sit atop the foundation, upon which the first floor joists rest. Rim joists, also known as band joists, are the boards that box in the floor joists. The ends of all floor joists resting on the sole plate but up against rim joists. Rim joists also help stabilize the joists and help keep them from angling or twisting.

In a properly designed brick veneer wall, a gap is supposed to be installed between the brick veneer and the exterior wall sheathing. The exterior sheathing is the material that covers the outside face of the wall framing. Sheathing can be boards (in older construction), or plywood or oriented strand board (OSB) panels, although in some construction Styrofoam panels may be installed between the plywood or OSB panels. The gap between the exterior sheathing and brick veneer is supposed to serve as a drainage plain to provide water that gets past the brick veneer a drainage path to the base of the wall. And, believe me; water can get past the brick veneer, particularly if the brick is especially porous. Drainage holes (in combination with flashing) in the brick veneer just above the foundation in the brick veneer are supposed to provide a path for water to flow out of the drainage plain. Brick veneer installed on concrete block construction, more commonly used for commercial construction, is also supposed to have a drainage plain with weep holes.

Full brick exterior walls, such as those on many old buildings in Cincinnati, do not need weep holes because the water supposedly travels fully through the brick into the interior wall surface or back out to the exterior surface. Another brick construction that was usually not built with drainage holes was concrete block on a concrete foundation with brick veneer installed in front of the block. Unlike the previously described brick veneer/concrete block wall, the first floor framing in this construction was built on the block and the upper floor framing was built above that. The brick veneer in this construction extended from the concrete foundation and up the exterior wall. This last construction, as used for a crawlspace construction, is the subject of this blog post.

Let’s start with a photo of the foundation construction from inside the crawlspace, shown below:


This photo shows the concrete foundation with the concrete block above it. On the exterior side of the foundation, the soil level would be to the top of the first row of concrete block above the foundation. Now, take note of the dark streaks on the facing concrete foundation. Those streaks are due to water drainage through openings in the block mortar. The question is from where is that water coming. For sure, water can migrate from the soil through the block. But, the darkened block in the area in the corner area and along the foundation to the left that extends the full height of the block hints at another source—the drainage gap behind the brick veneer. Darkening of the block indicates that they are water-saturated. Further support for the drainage gap being a water source is evident from the darkened sole plate wood sitting on top of the darkened concrete block.

Let’s take a closer look at part of the area along the facing foundation. Note the copper water pipe in the photo above. This pipe is the same as the one shown to the left in the photo below. In this photo, the darkened woods of the sole plate and rim joist above the water-saturated concrete block is visible. However, also visible are darkened areas in the subfloor boards on top of the joists. The material that looks like resin or droplets is water droplets on the wood surfaces. The pattern of the water stains on the subfloor indicates that the water source is the exterior wall, and more particularly the drainage gap behind the brick veneer. Areas like these were found all along the exterior walls of this crawlspace foundation.


So, what do these findings have to do with termites—as it turns out, a lot. Termites are one of Nature’s maintenance creatures. They reduce wood back into a form that is useful to plants, microflora and soil. The trouble is that they cannot distinguish between the dead wood of a tree in the forest and the lumber we use in our buildings. The subterranean termites we have in the Cincinnati area also require water to live. In fact, they build mud and frass tubes in areas where they would be exposed to air to conserve water and will carry water from the soil into the tubes to keep them damp enough. In the photo below, the dark streaks on the foundation are the remains of such tubes between the ground and the sole plate. Note that the distance between the ground and the sole plate in the photo is about 5 feet. Termites can be very determined to find a food source.


If termites can find wet wood, their job gets much easier because they do not have to bring as much (if any) water up from the ground. So, in the case of this home, they found it in the wet sole plate and rim joist woods. And once they set up their work area in them, they went to town. The following photos show some of the visible damage. Note in all of these photos that the wood is darkened due to water exposure.




I want to emphasize the words “some of the visible damage.” The exact extent of the damage generally would only be known when the damaged wood is removed and inspected. An ice pick or awl can be used to probe the wood and somewhat determine the extent of damage. If the damage is on the other side of solid wood, though, this method would not find it. Also, termites form multiple tunnels in the wood, which means that unless the wood has been greatly degraded by the tunnels, as in the photos, a lot of probing would be needed to fully determine the damage. More sophisticated and expensive methods to determine the extent of damage exist, such as injecting chilled or heated air into the termite tunnels in the wood and viewing the wood using a thermal camera. In theory, the air would follow the tunnels and provide a temperature difference within the wood that is visible to the camera. The common method, however, is using a probe.

The damaged wood in this home will need to be removed, which will be expensive due to where it is located. The repair will also not be as ideal as new construction. Even worse, as wood is removed, more damaged wood that is not readily visible might be found, making the project much more expensive.

But, a question still exists as to why the sole plate and rim joist wood is getting wet when the wood is at least 16 inches above outside grade. Additionally, the drainage plain behind the brick should extend below the wood to the concrete foundation level. I believe that a couple of possibilities exist. The brick might not have a proper drainage plain, in that the brick veneer is right up against the exterior sheathing. I hope not because that likely means the exterior sheathing and upper floor framing could have moisture and/or termite damage. Another possibility is that the rim joists and/or sill plates block the drainage plain. Then again, water from the upper drainage plain may be filling up the concrete block and/or the gap between the brick and block to the level of the wood. Overall, though, the fact that the subfloor appears to be getting wet indicates that a drainage plain issue is present. When the wood is replaced, the real water source might be evident.

What are the morals of this story? Here are a few:

  • Damp crawlspaces or basements can be an invitation for termites to move in.
  • Properly designed and installed drainage plains behind exterior finishes, whether brick veneer or siding, can help prevent expensive repairs.
  • A great amount of water can penetrate through brick.
  • Trick observation—the crawlspace floor was muddy apparently due to water flowing into it. Since no vapor barrier was present, water from the wet soil can evaporate and enter the home where it can cause mold growth in those dark and quiescent locations where mold likes to hang. Then again, even a vapor barrier might not help if too much water is getting into the crawlspace.

Unfortunately, like most projects of this kind, I will not know the outcome due to the nature of these kinds of projects. Be assured that if I hear anything, you will be the first to know.

General Guidance and Anchoring System Options for Manufactured and Modular Home with Perimeter Support Foundations (REV.)

January 30, 2011

Overview:

This document discusses the proper methods (and more than one exists) for anchoring manufactured and modular homes with perimeter support foundations, which will be better defined just a little further on. The subject of this document is primarily proper anchoring methods because I frequently find mistakes in these anchoring systems. In my internet searches, I have not come across other publications that specifically address this topic. Building codes and other regulations, such as the Housing and Urban Development’s model regulations, and manufacturer installation instructions describe or dictate construction of other foundation elements and the installation of the home; but details on anchoring requirements for these foundation systems is sketchy.

Therefore, I wrote this document to summarize the anchoring methods, and errors in anchoring methods, that I have found while performing over 500 FHA or other inspections on these homes (and all of the photos in this document came from those inspections). This document covers both manufactured and modular homes because some of the home constructions have very similar foundation and anchoring systems. Although Criterium-Cincinnati Engineers does not get many calls for modular home inspections, those I have inspected leads me to believe that the prevalence in anchoring issues are similar to those for manufactured homes.

Note that this article and its contents are only intended as guidance. It is not intended to be used as a design document or to replace any building codes or other applicable rules. Be sure to check local and state building code or other state installation rules for specific installation requirements.

General Guidance for Manufactured and Modular Home Foundation Systems:

Manufactured and modular homes mainly differ visually in that manufactured homes arrive on-site on their own wheels while modular homes are transported on-site via another carrier, such as a flat-bed trailer. For a more detailed description of differences, refer to these web sites:

The majority of the manufactured and modular homes have pier (rather than perimeter) foundation systems. Photo 1 shows a typical pier system:

Photo 1. Typical manufactured home pier system.

This foundation system uses piers, commonly constructed from concrete blocks (seen in the photo above) for the foundation system. The piers are supposed to be erected on either poured concrete footings or slabs For manufactured and on-frame modular homes that have I-beam structural members that are part of the home structure, the piers are located under and support the I-beams. (For manufactured homes, these beams are commonly called carriage beams because they are used to transport the home to the site. To use common terminology for both manufactured and modular homes, I use “home structural beams” in this document.)

Vinyl skirting or a concrete block perimeter wall is usually installed around underside of the perimeter of the home to enclose the pier foundation system. This skirting or perimeter wall is not part of the foundation system and is not structural. Skirting and perimeter walls have purpose, though, in that they help keep water and vermin from getting under the home, help protect the plumbing from freezing and prevent wind (more particularly high winds) from getting under and lifting the home.

Manufactured homes come in both single and doublewide constructions, while modular homes are usually doublewide construction. Singlewide means that the home is a complete home, constructed so that it can be moved into place as a unit and set on the foundation system. Doublewide structures arrive on-site in two halves that are moved together on a foundation system and the halves are then screwed together. Each half of the doublewide home comes with a hinged roof. Once the two halves of a doublewide are assembled, the roof is rotated into position and assembled. Although not yet common, complex manufactured and modular homes, such as multiple story structures, are being built. Foundation systems for the more complex structures are similar to the single-story structures, although adjusted for the extra weight.

Both single and double-wide homes would have piers under the home structural beams, while a double-wide home would also have additional piers supporting points along the home’s marriage line, as specified by the manufacturer. (The marriage line, which is sometimes also known as the mating line, is where the two halves of a double-wide home meet.) The anchoring systems for pier foundations for manufactured and on-frame modular homes is either a lateral brace system or steel straps with concrete or ground anchors, which are shown in Photos 2 and 3, respectively.

Photo 2. An example of one manufacturer’s lateral brace anchored to a concrete slab.

This article, though, is about anchoring manufactured and modular homes that have perimeter foundation systems. The terminology “perimeter foundation system” might inspire a mind picture of the typical site-built home foundation system where the perimeter of the home is supported directly on the foundation system. Some manufactured and modular home foundation systems are similar to site-built home foundation systems, and they are discussed later in this article. However, most manufactured and on-frame modular homes with perimeter foundation systems are supported on H or I-beams that are in turn supported on the perimeter foundation system. In this article, these beams are called foundation beams (and can be seen in the photo below). Homes with foundation beams have different anchoring requirements than homes without foundation beams, and the former are discussed first. A typical foundation beam installation is shown in the Photo 4.

Photo 3. An example of one manufacturer’s steel strap anchored to a concrete slab.

As the photos throughout this article show, perimeter foundation systems can be used for either basement or crawlspace foundations. Normally, though, foundation systems with center-support steel columns are used in homes with basements to allow for possible finishing of the basement. Basements and crawlspaces could have either gravel or concrete slab floors; but all should have footings installed under the center support columns or piers.

Manufactured and modular home perimeter foundations are constructed from either poured concrete or concrete block, similar to site-built homes. Local building codes usually dictate how foundations should be constructed. If the area has no local building codes, construction usually has to adhere to state building codes, which are usually a derivation of the International Building Codes (although the state’s current building codes might not be as current as the International Building Codes). Homes installed in areas under the jurisdiction of a building department usually need to have a building department permit and at least a foundation system inspection. Further, installation permitting and inspection requirements can vary from state to state and even from area to area. Be sure to check local building code requirements specific to manufactured and modular homes. Concrete foundations usually have pockets built in the walls to support the ends of the foundation beams similar to the pockets installed in site-built home foundations to support the ends of these homes’ main beams. Concrete block foundations usually have pilasters installed to support the beam ends, and the concrete blocks that comprise the pilasters need to have their holes completely filled with concrete. The concrete fill needs to have rebar reinforcement installed in the concrete. That being said, some concrete block foundations have pockets for the foundation beams instead of pilasters and some poured concrete foundations have pilasters for the foundation beams instead of pockets. Still, even if pockets are installed in a concrete block foundation, pilasters are still usually built in the foundation under the pockets and the blocks are filled with concrete with rebar reinforcement. Examples of foundation beam installations are shown in Photos 5 through 7.

Photo 4. An example of a manufactured home with a perimeter foundation system that uses foundation beams and concrete block center piers.

The ends of all structural beams for manufactured and on-frame modular homes need to be supported. In Photo 8, pilasters built next to the end foundation wall are used to support the structural beams. Other acceptable means for supporting the ends of the structural beams that I have found were pilasters built into the foundation walls, steel columns or foundation beams. Unlike the pilasters supporting the structural beams, concrete block columns do not have to be fully mortared, but must have proper cap blocks, which are usually half-filled 8-inch or 4-inch thick concrete blocks or 2-inch minimum hardwood boards that are at least the same dimensions as the pier blocks. Piers and steel columns need to have proper footings. If foundation beams, piers or steel columns are used instead of pilasters to support the ends of the home structural beams, they need to be located within 2 feet of the ends of the home structural beams.

Photo 5. Example of a foundation beam installed in a pocket on top of a pilaster in a concrete block foundation wall.

Photo 6. Example of a foundation beam installed on a pilaster of a concrete block foundation without a pocket.

Photo 7. Example of a foundation beam installed in a pocket in a poured concrete foundation wall.

Photo 8. An example of piers supporting a manufactured home’s structural beams.


Photo 9. An example of shimming for the end of a home structural beam.

 

As Photo 9 shows, the ends of the structural beams may need shimming. While the home’s structural beams are shimmed, the foundation beams are not normally shimmed. When wood shims are used, they need to be a minimum 4-inch wide hardwood and used in pairs, as shown in the photo. Shims are not usually used between the foundation or pilasters and the foundation beams. The reason is that the home is usually leveled by installing shims between the foundation beams and the home structural beams because adjustment needed between one foundation beam/structural beam contact point and another can vary significantly. Shims are also sometimes used between the middle support piers and the foundation beams. The proper shims between the home structural and foundation beams will be discussed in more detail later in this article. But the shims between the middle support piers and the foundation beams are a minimum 4-inch wide hardwood and used in pairs

As Photos 4 and 10 show, the foundation beams are located in nearly the same locations as would be the piers for a pier foundation home. That is, steel beams run the width of the home in similar locations to the piers and support the home’s structural beams and marriage line (if needed) in the same way as the piers. The ends of the foundation beams are supported on the home’s front and rear perimeter walls.

Photo 10. An example of a perimeter foundation system that uses foundation beams and center support
columns.

Double-wide homes usually have either concrete block piers or steel columns supporting the center of the foundation beams. Photo 10 shows an example of steel columns while Photo 11 shows an example of concrete block piers. Columns need to be fastened at the bottom to the footing or slab and at the top to the foundation beam or other marriage line structure, which will be discussed later. These fastening requirements hold true for other locations steel piers might be used, such as at the ends of the home structural beams.

Depending on the manufacturer requirements, extra piers may be needed to support the marriage line at other locations other than above the foundation beams, as shown in the Photo 11. Installation instructions usually show where marriage line piers are needed. For newer homes, most manufacturers indicate where support is needed along the marriage line with some kind of mark on the bottom board (the membrane covering the underside of the home). If the manufacturer calls for support of the marriage line at a point less than 2 feet from a foundation beam, then additional support may not be needed.

I have been asked whether piers have to be unmortared (a.k.a. dry-stacked) or mortared. Mortaring is required in Housing and Urban Development (HUD) 7487. Permanent Foundations Guide for Manufactured Housing, the guidelines used for foundation inspections for Federal Housing Authority (FHA) loan approval. The latest HUD standard (24 CFR 3285. Model Manufactured Home Installation Standards) used as a model for current manufactured home installations does not require mortaring of any foundation pier blocks, including the marriage line piers, unless they are specially designed or in flood plains. This standard does require piers from 32 to 60 inches to be double-stacked, as shown in Photo 11, and piers over 60 inches to be designed by a licensed engineer or architect. Additionally, the standard requires that ALL piers for homes in flood plains be designed by a licensed engineer or architect and meet the requirements of the local flood plain authority. But, the standard provides no information for the piers used in perimeter foundation systems other than they are designed by a licensed engineer or architect or adhere to the manufacturer’s installation instructions. I have found both mortared and unmortared marriage line and end support piers. I have also not found any issues with properly installed unmortared piers built on properly designed and installed footings.

Homes that have steel columns instead of piers may also need to have support for the marriage line that is farther than 2 feet from the foundation beams. In these cases, additional steel columns can be installed, or if a wall has been installed under the marriage line, for example as part of finishing a basement, the wall can be extended to the marriage line to provide support. However, that wall then becomes a load-bearing wall. Other methods can also be used to support the marriage line between foundation beams; but a licensed engineer or architect should be hired to specify such construction.

Double-wide homes also have blocking installed on top of the foundation beams above all center piers to support the marriage line. Foundation systems that use steel columns instead of piers to support the foundation beams also have blocking is installed on top of the foundation beams above the columns, as shown in Photo 12. Blocking is usually wood, although concrete blocks can also be used as long as a cap block is installed on top of the blocks, as visible in Photo 11. Blocking needs to be at least the width of the foundation beam flange and at least twice as long as wide to assure stability.

Gaps between the top of piers and blocking along the marriage line need to be shimmed. Shims need to be at least 4 inches wide, hardwood or equivalent and used in pairs. These shims need to be driven tight between the pier or blocking and the marriage line.

For information on the currently acceptable construction piers, please refer to 24 CFR 3285: MODEL MANUFACTURED HOME INSTALLATION STANDARD (http://www.access.gpo.gov/nara/cfr/waisidx_08/24cfr3285_08.html) or your state’s current installation standards (which should be a derivation of 24 CFR 3285). Keep in mind that these standards defer to the manufacturer’s installation instructions, if available. Installers should read and follow the manufacturer’s installation instructions. Not following the manufacturer’s instructions could void the home’s warranty or the expose the installer or others to liability issues. The information presented in this article is not intended to replace the installation instructions.

Photo 11. Examples of concrete block piers under the marriage line and mid-point of the foundation beam.

Photo 12. Examples of marriage line support blocking and a steel column support under the mid-point of a foundation beam.

Anchoring Systems for Perimeter Foundation Systems:

To properly anchor manufactured and on-frame modular homes with perimeter foundations, the foundation beams need to be anchored to the foundation AND the home structural beams need to be fastened to the foundation beams supporting them. This latter part of the anchoring system seems to be most often forgotten or unknown. No one method exists for anchoring the foundation beams to the foundation; but the anchoring method needs to meet these basic criteria:

  • BOTH ends of all foundation beams need to be anchored to the foundation.
  • If the foundation beam ends are not located in pockets that are tight enough to prevent twisting or sideways movement of the beams, both sides of each end of the foundation beams need to be anchored or the full widths of the beams have to be anchored (as shown in the example photos later in this article).
  • The anchors have to prevent the foundation beams from being pulled laterally out of the pockets or off the pilasters, as could happen if the foundation wall moves outward.
  • The anchors have to prevent the foundation beams from being pushed sideways off of the pilasters.
  • The anchors or the foundation pockets have to prevent the ends of the foundation beams from being lifted vertically off of the pilasters or within the pockets.

Manufactured and on-frame modular homes installed on poured concrete foundations have more anchoring options than concrete block foundations because anchors for the latter need to be tied to the reinforcement in the concrete-filled blocks in the foundation. Photos in this section show examples of a variety of anchoring methods that I have found during inspections of manufactured homes with foundation beams.

Photo 13 shows the end of a foundation beam on top of a pilaster. By far the most common method for anchoring foundation beams to concrete block foundations is using the rebar installed to reinforce the pilaster. As shown, the rebar is extended above the pilaster, and bent over onto and welded to the foundation beam, as shown in the photo. This photo shows the preferred method for attaching the rebar to the beam in that the rebar ends are kept short and at least 2 inches of the rebar is welded solidly to the beam (indicated by the arrow). A similar rebar anchor is on the other side of the beam to prevent the beam from moving sideways on the pilaster. Both sides of each rebar end should be welded to the beam.

Photo 14 shows another variation of a rebar anchor that is acceptable, although not as ideal as the previous photo. In this installation, a similar rebar anchor was installed on the other side of the beam. This anchor would be more ideal if the area around the base of the rebar inside the block were mortared to stiffen the rebar.

Photo 15 shows another rebar/beam anchor that is not acceptable. As this photo shows, the rebar is much longer than those shown in Photos 13 and 14. Although the longer rebar means that it can be bent into position more easily, the longer rebar does not restrain the beam from excessive movement. Furthermore, only the very end of the rebar is welded, which could allow the rebar to break loose if the beam moved. A closer pocket around the beam would restrict the beam from moving sideways; but the excessive length of the rebar would not prevent is from being pulled from the pocket. This anchor could be fixed by shortening the rebar on both sides of the beam and welding at least 2 inches of the rebar to the beam.

Photo 13. Example of pilaster rebar being used also as an anchor for a foundation beam.

Photo 14. Another example of pilaster rebar also being used to anchor a foundation beam.

:

Photo 15. Example of pilaster rebar being used improperly as an anchor for a foundation beam.

Improper welding of the rebar is a common issue with the rebar anchor, as shown in the Photo 15. If enough off the rebar is not welded to the foundation beam, the weld can break loose, as indicated by the arrow Photo 16. In this case, the installer apparently tack welded the rebar and the weld had later broken loose simply by the rebar pulling upward on the weld. If the weld could break loose simply due to the rebar force, imagine the rebar trying to prevent the beam from moving. As with the case shown in Photo 15, to fix this issue, the rebar should be shortened first and at least 2 inches of the rebar welded the beam

Photo 17 shows a gross misuse of a rebar anchor. As the photo below shows, the rebar is run from the foundation footing to the foundation beam. Obviously, this anchor would not constrain movement of the foundation beam and would therefore not be an acceptable anchor. This photo also shows another issue with the pilaster construction. Gaps in the mortar show that the blocks were not fully mortared, nor filled with concrete or reinforced with rebar.. At least, this installer used a sold 4-inch concrete block on top of the pilaster to properly transfer the beam load fully across the pilaster.

Photo 16. Another example of an improper rebar anchor; but in this case, the rebar has pulled loose due to not being welded properly.

Photo 17. Another example of an improper rebar anchor for a foundation beam. Also shown is an example of an improperly constructed pilaster.

As stated previously, poured concrete foundations offer additional anchoring options as shown in the following Photos 18 and 19.

Photo 18. Example of a proper foundation beam anchor using angle iron that has been bolted to foundation and welded to the foundation beam.

Photos 18 and 19 show two variations of the same type of anchor, except one was installed under the foundation beam and the other over the foundation beam. Both photos show that the anchor is bolted solidly to the foundation and both are wider than the beam flanges. The foundation beams need to be welded fully to the anchors, as can be seen clearly in Photo 19. Even if the anchor is installed above the beam, welding is needed to prevent the beam from being pulled upward or out of the pocket. Note also that the beam pockets in both photos are just wide enough to accommodate the beam, which helps prevent beam twist. However, these types of anchors should also help prevent twist.

Photo 20 shows a clever use of tie-down straps normally used to anchor homes on pier foundation systems. In this case, the straps normally used to fasten piered home’s structural beams to a concrete footing or pad have been used to anchor this home’s structural beams the concrete foundation. Further, the strap has been properly looped around the carriage beam according to the manufacturer’s instructions, which firmly secures the strap buckle to the home structural beam. Many installers do not properly install these straps. The additional strap between the carriage beam and the end foundation wall should not be needed because the home structural beam’s movement is constrained by the foundation and other anchors; but the manufacturer’s installation instructions should be followed to prevent voiding warranties. Nonetheless, this installation does not meet the overall guidelines stated earlier because the foundation beams have not been anchored to the foundation or the structural beams have not been fastened to the foundation beams. Note also that this photo shows an example of an installation with a foundation beam installed near the end of the home structural beams instead of a pilaster, pier or column.

Photo 19. Example of another proper anchoring method using angle iron bolted to foundation.


Photo 20. Example of an anchor method using steel strap anchors attached to the foundation.

In some cases, concrete block is sometimes installed on top of a poured concrete foundation. This kind of change can happen if additional headroom in a basement was desired after the concrete foundation has already been poured. Photo 21 shows the way one installer, almost acceptably resolved this issue. The installer built pockets in the block to constrain the foundation beams and then welded angle anchors to the beams that extended to the poured concrete foundation. However, the installer did not bolt the angles to the foundation, making this installation not acceptable. The installer also did reinforce the concrete blocks surrounding the foundation beams by installing rebar that was anchored into the concrete foundation and filling the block holes with concrete. In fact, I believe that the designer should have specified that all of the concrete block sections be reinforced and concreted.


Photo 21. Example of a possible proper foundation beam anchor used on a mixed materials foundation. However, the angle section needs to be bolted to the foundation.

To complete a proper anchoring system for foundation beam systems, the home structural beams need to be fastened to the foundation beams. Manufacturer installation instructions that I have reviewed require that the structural beams be fastened to the foundation beams at ALL points where they cross. Manufacturers usually allow two fastening methods, either 1/4″-inch fillet welds or bolting. An example of welding is shown in Photo 22 and bolting in Photo 23.

Photo 22. Example of a proper welding between a structural beam and foundation beam.

Photo 23. Example of a bolt fastening a structural beam to a foundation beam.

By far, welding is usually more expedient than bolting and more secure. Installers considering bolting should check with the manufacturer to assure that drilling holes in the home structural beams will not void the home’s warranty. If bolting is allowed, installers should also check for the manufacturer’s specifications for bolt size and torque. Installers should also verify whether washers and lock nuts are needed. Installation instructions for welding usually require that both sides of either the home structural or foundation beam be welded; but installers should follow the manufacturer’s specific instructions for the home. Installation instructions also normally require that each joint be fully welded across the full width of the structural or foundation beam, as shown in Photo 22. A number of installers us a weld of only 1 or 2 inches, which is normally not acceptable. Alternative methods of fastening the two beams together may exist; but the installer should check with the manufacturer for acceptability. In the absence of installation instructions, installers should follow local building codes requirements for fastening the beams together.

Earlier in this article, I noted that shims are normally installed between the foundation beams and home structural beams rather than between the foundation beams and the foundation. Wood shims, as shown in Photo 24, are not acceptable because they may not support the load and they do not allow proper fastening of the foundation beams to the home structural beams. Additionally, when joints with shims are welded, the shim needs to be fully included in the weld, as shown in Photo 25.

Photo 24. Improper use of wood shims between a foundation beam and structural beam.

Photo 25. Proper welding of the metal shims used between a structural beam and foundation beam.

Alternative Foundation Systems and Anchoring Methods:

Previously, I mentioned a second general type of manufactured and modular home construction that is supported directly on the perimeter foundations without need for foundation. From the underside, these homes look very similar to site-built homes, as can be seen in the Photos 26 through 28. The first two photos are manufactured homes and the last photo is a modular home. The marriage line of these homes are usually supported on steel columns or concrete block piers. A load-bearing wall could also be used instead of columns; but, the homes I have inspected that had frame walls built under the marriage line also usually had steel columns. If a frame wall is planned to be used as a load-bearing wall instead of steel columns, consult the manufacturer’s installation instructions or local building codes to verify that load-bearing wall construction is acceptable.

Note that in Photos 26 through 28 the marriage line is the equivalent of the main beam in a site-built home, except one-half of the marriage line “beam” belongs to each side of the home. The two halves are screwed together when the homes are mated together. These homes come in a variety of constructions, and manufacturers are likely to make changes in the future to make the homes look even more like site-built homes.

Another difference between these homes and those with foundation beams is that these homes are anchored around the perimeter to a sole plate that sits on top of the foundation. To fully anchor these homes, the sole plate must be anchored to the foundation AND the home needs to be anchored to the sole plate.

Photo 26. Example of one style of manufactured home that uses perimeter anchoring to a sole plate instead of foundation beams.

Photo 27. Another example one style of manufactured home that uses perimeter anchoring to a sole plate instead of foundation beams.

 

Photo 28. Example of one style of modular home that uses perimeter anchoring to a sole plate instead of foundation beams.

Two methods for anchoring the sole plate are shown in the following Photos 29 and 30. Photo 29 shows a sole plate anchored to the foundation using an anchor bolt while Photo 30 shows a sole plate attached to the foundation using metal straps fastened to the foundation. Some installers have also used concrete anchors and bolts to fasten the sole plate to the foundation. Local or state building codes, the International Building Code or the manufacturer instructions should be consulted to determine acceptable methods for how the sole plate is fastened to the foundation. Keep in mind that the weaker the fastening method, the more anchors might be needed. For example, I would expect fewer anchors being needed for the anchor bolt fasteners in Photo 29 than the strap anchors in Photo 30.

I have observed two variations in home construction that determine how the home is anchored to the sole plate. For homes with wood joists, the joists can be fastened to the sole plate directly, as shown in Photo 31. In this installation, the sole plate was oversized and lag screws were used to screw joists to the sole plate.

Homes with steel joists may have a sole plate attached to the bottom of the joists, as shown in the Photo 32. As can be seen in this photo, this sole plate is then screwed to the foundation sole plate.

Photo 29. Example of a sole plate bolted to the foundation. The home is then fastened to the sole plate.

Photo 30. Example of a strap anchor being used to anchor a sole plate to foundation.

Photo 31. Example of a home joist being screwed to the sole plate to complete the anchoring system.

Photo 32. Example of a manufactured home bolted to a sole plate.

Some homes have band joists that extend below the floor joists, which can be seen as oriented strand board in Photo 29. For these homes, the band joist can be fastened to the sole plate from the exterior side of the rim joist prior to siding being installed over the band joist. On the other hand, some manufacturers extend the exterior sheathing below the floor level and attach the joists to the sheathing, which appears to be the case in Photo 30. Manufacturers may have specified methods for anchoring the home in the installation instructions. If the instructions do not specify an anchoring method, refer to local or state building codes or contact the manufacturer or a licensed engineer or architect for recommendations.

Although manufacturers might allow anchoring the home using the rim joist or exterior sheathing, I do not favor this method of anchoring. One major issue with this anchoring method is that a gap is sometimes left between the exterior sheathing or band joist and the sole plate because of an error or inaccuracy in construction. This gap could be sizeable. For one home I inspected, a gap of nearly 1 inch was present in some places around the home’s perimeter. The strength in this anchoring method comes mainly from the contact between the sheathing or band joist and the sole plate woods when the fastener pulls them together. If a gap is present, the fasteners take the entire load, which weakens the anchor. Additionally, verifying whether the home has been properly anchored is difficult to impossible once the siding has been installed. Due to the number of issues with this method of anchoring the home, I recommend that an alternate method that anchors the home’s joists to the sole plate be used if possible.

The Wrap:

I have tried to be as thorough as possible in writing this article; however, I have likely missed some important points. Further, manufacturers periodically change designs that could change installation requirements. Further, so much variation exists currently in home designs that a particular home’s foundation system and anchoring method may be different than presented in this article; but those in this article may still be acceptable.

Another important point is that recent HUD rules require states to develop installation rules based on the HUD model standards (24 CFR 3285). HUD further required that new manufactured home sets be inspected according to each state’s rules. For installations not covered in the HUD or state rules, such as perimeter foundation systems, HUD rules and likely many state rules defer to the manufacturer’s installation instructions or specifications by a licensed engineer or architect designs. If other state rules are similar to those in Ohio, this information must be obtained prior to obtaining a permit to begin construction. Make sure you are aware of your state’s requirements so that a potentially stiff fine or reconstruction costs are avoided.

Please be sure to contact us with questions or comments or to request a PDF version of this article. I hope to revise this article based on those comments and questions.

General Guidance and Anchoring System Options for Manufactured and Modular Homes with Perimeter Support Foundations

January 16, 2011

Overview:

This document discusses the proper methods (and more than one exists) for anchoring manufactured and modular homes with perimeter support foundations, which will be better defined just a little further on. The subject of this document is primarily proper anchoring methods because I frequently find mistakes in these anchoring systems. In my internet searches, I have not come across other publications that specifically address this topic. Building codes and other regulations, such as the Housing and Urban Development’s model regulations, and manufacturer installation instructions describe or dictate construction of other foundation elements and the installation of the home; but details on anchoring requirements for these foundation systems is sketchy.

Therefore, I wrote this document to summarize the anchoring methods, and errors in anchoring methods, that I have found while performing over 500 FHA or other inspections on these homes (and all of the photos in this document came from those inspections). This document covers both manufactured and modular homes because some of the home constructions have very similar foundation and anchoring systems. Although Criterium-Cincinnati Engineers does not get many calls for modular home inspections, those I have inspected leads me to believe that the prevalence in anchoring issues are similar to those for manufactured homes.

Note that this article and its contents are only intended as guidance. It is not intended to be used as a design document or to replace any building codes or other applicable rules. Be sure to check local and state building code or other state installation rules for specific installation requirements.

General Guidance for Manufactured and Modular Home Foundation Systems:

Manufactured and modular homes mainly differ visually in that manufactured homes arrive on-site on their own wheels while modular homes are transported on-site via another carrier, such as a flat-bed trailer. For a more detailed description of differences, refer to these web sites:

The majority of the manufactured and modular homes have pier (rather than perimeter) foundation systems. The following photo shows a typical pier system:

This foundation system uses piers, commonly constructed from concrete blocks (seen in the photo above) for the foundation system. The piers are supposed to be erected on either poured concrete footings or slabs For manufactured and on-frame modular homes that have I-beam structural members that are part of the home structure, the piers are located under and support the I-beams. (For manufactured homes, these beams are commonly called carriage beams because they are used to transport the home to the site. To use common terminology for both manufactured and modular homes, I use “home structural beams” in this document.)

Vinyl skirting or a concrete block perimeter wall is usually installed around underside of the perimeter of the home to enclose the pier foundation system. This skirting or perimeter wall is not part of the foundation system and is not structural. Skirting and perimeter walls have purpose, though, in that they help keep water and vermin from getting under the home, help protect the plumbing from freezing and prevent wind (more particularly high winds) from getting under and lifting the home.

Manufactured homes come in both single and doublewide constructions, while modular homes are usually doublewide construction. Singlewide means that the home is a complete home, constructed so that it can be moved into place as a unit and set on the foundation system. Doublewide structures arrive on-site in two halves that are moved together on a foundation system and the halves are then screwed together. Each half of the doublewide home has comes with a hinged roof. Once the two halves of a doublewide are assembled, the roof is rotated into position and assembled. Although not yet common, complex manufactured and modular homes, such as multiple story structures, are being built. Foundation systems for the more complex structures are similar to the single-story structures, although adjusted for the extra weight.

Both single and double-wide homes would have piers under the home structural beams, while a double-wide home would also have additional piers supporting points along the home’s marriage line, as specified by the manufacturer. (The marriage line, which is sometimes also known as the mating line, is where the two halves of a double-wide home meet.) The anchoring systems for pier foundations for manufactured and on-frame modular homes is either a lateral brace system or steel straps with concrete or ground anchors, which are shown in the photos below:

An example of one manufacturer’s lateral brace anchored to a concrete slab, in this case.

An example of one manufacturer’s steel strap anchored to a concrete slab, in this case.

This article, though, is about anchoring manufactured and modular homes that have perimeter foundation systems. The terminology “perimeter foundation system” might inspire a mind picture of the typical site-built home foundation system where the perimeter of the home is supported directly on the foundation system. Some manufactured and modular home foundation systems are similar to site-built home foundation systems, and they are discussed later in this article. However, most manufactured and on-frame modular homes with perimeter foundation systems are supported on H or I-beams that are in turn supported on the perimeter foundation system. In this article, these beams are called foundation beams (and can be seen in the photo below). Homes with foundation beams have different anchoring requirements than homes without foundation beams, and the former are discussed first. A typical foundation beam installation is shown in the photo below:

An example of a manufactured home with a perimeter foundation system that uses foundation beams and concrete block center piers.

As the photos throughout this article show, perimeter foundation systems can be used for either basement or crawlspace foundations. Normally, though, foundation systems with center-support steel columns are used in homes with basements to allow for possible finishing of the basement. Basements and crawlspaces could have either gravel or concrete slab floors; but all should have footings installed under the center support columns or piers.

Manufactured and modular home perimeter foundations are constructed from either poured concrete or concrete block, similar to site-built homes. Local building codes usually dictate how foundations should be constructed. If the area has no local building codes, construction usually has to adhere to state building codes, which are usually a derivation of the International Building Codes (although the state’s current building codes might not be as current as the International Building Codes). Homes installed in areas under the jurisdiction of a building department usually need to have a building department permit and at least a foundation system inspection. Further, installation permitting and inspection requirements can vary from state to state and even from area to area. Be sure to check local building code requirements specific to manufactured and modular homes.

Concrete foundations usually have pockets built in the walls to support the ends of the foundation beams similar to the pockets installed in site-built home foundations to support the ends of these homes’ main beams. Concrete block foundations usually have pilasters installed to support the beam ends, and the concrete blocks that comprise the pilasters need to have their holes completely filled with concrete. The concrete fill needs to have rebar reinforcement installed in the concrete. That being said, some concrete block foundations have pockets for the foundation beams instead of pilasters and some poured concrete foundations have pilasters for the foundation beams instead of pockets. Still, even if pockets are installed in a concrete block foundation, pilasters are still usually built in the foundation under the pockets and the blocks are filled with concrete with rebar reinforcement. Examples of foundation beam installations are shown below:



(Top photo) Example of a foundation beam installed in a pocket on top of a pilaster in a concrete block foundation wall.

(Middle photo) Example of a foundation beam installed on a pilaster of a concrete block foundation without a pocket.

(Bottom photo) Example of a foundation beam installed in a pocket in a poured concrete foundation wall.

The ends of all structural beams for manufactured and on-frame modular homes need to be supported. In the photo below, pilasters built next to the end foundation wall are used to support the structural beams. Other acceptable means for supporting the ends of the structural beams that I have found were pilasters built into the foundation walls, steel columns or foundation beams. Unlike the pilasters supporting the structural beams, concrete block columns do not have to be fully mortared, but must have proper cap blocks, which are usually half-filled 8-inch or 4-inch thick concrete blocks or 2-inch minimum hardwood boards that are at least the same dimensions as the pier blocks. Piers and steel columns need to have proper footings. If foundation beams, piers or steel columns are used instead of pilasters to support the ends of the home structural beams, they need to be located within 2 feet of the ends of the home structural beams.

As the photo below shows, the end of the beam is shimmed. Where the home’s structural beams are shimmed, the foundation beams are not normally shimmed. When wood shims are used, they need to be a minimum 4-inch wide hardwood and used in pairs, as shown.

As mentioned previously, while the ends of the home structural beams are shimmed, shims are not usually used between the foundation or pilasters and the foundation beams. The home is usually leveled by installing shims between the foundation beams and the home structural beams because adjustment needed between one foundation beam/structural beam contact point and another can vary significantly. Shims are sometimes used between the middle support piers and the foundation beams. The proper shims between the home structural and foundation beams will be discussed in more detail later in this article.

As the previous and following photos show, the foundation beams are located in nearly the same locations as would be the piers for a pier foundation home. That is, steel beams run the width of the home in similar locations to the piers and support the home’s structural beams and marriage line (if needed) in the same way as the piers. The ends of the foundation beams are supported on the home’s front and rear perimeter walls.

An example of a perimeter foundation system that uses foundation beams and center support columns.

Double-wide homes usually have either concrete block piers or steel columns supporting the center of the foundation beams. The above photo shows an example of steel columns while the below photo shows an example of concrete block piers. Columns need to be fastened at the bottom to the footing or slab and at the top to the foundation beam or other marriage line structure, which will be discussed later. These fastening requirements hold true for other locations steel piers might be used, such as at the ends of the home structural beams.

Depending on the manufacturer requirements, extra piers may be needed to support the marriage line at other locations than above the foundation beams, as shown in the photo below. Installation instructions usually show where marriage line piers are needed and, for newer homes, most manufacturers indicate where support is needed along the marriage line with some kind of mark on the bottom board (the membrane covering the underside of the home). If the manufacturer calls for support of the marriage line at a point less than 2 feet from a foundation beam, then additional support may not be needed.

Homes that have steel columns instead of piers may also need to have support for the marriage line that is farther than 2 feet from the foundation beams. In these cases, additional steel columns can be installed, or if a wall has been installed under the marriage line, for example as part of finishing a basement, the wall can be extended to the marriage line to provide support. However, that wall then becomes a load-bearing wall. Other methods can also be used to support the marriage line between foundation beams; but a licensed engineer or architect should be hired to specify such construction.

Double-wide homes also have blocking installed on top of the foundation beams above all center piers to support the marriage line. Foundation systems that use steel columns instead of piers to support the foundation beams also have blocking is installed on top of the foundation beams above the columns, as shown in the photo below. Blocking is usually wood, although concrete blocks can also be used as long as a cap block is installed on top of the blocks, as visible in the photo above. Blocking needs to be at least the width of the foundation beam flange and at least twice as long as it is wide to assure stability.

Gaps between the top of piers and blocking along the marriage line need to be shimmed. Shims need to be at least 4 inches wide, hardwood or equivalent and used in pairs. These shims need to be driven tight between the pier or blocking and the marriage line.

For information on the acceptable construction of the piers, please refer to 24 CFR 3285: MODEL MANUFACTURED HOME INSTALLATION STANDARD (http://www.access.gpo.gov/nara/cfr/waisidx_08/24cfr3285_08.html) or your state’s current installation standards (which should be a derivation of the Model Manufactured Home Installation Standards). Keep in mind that these standards defer to the manufacturer’s installation instructions, if available. Installers should read and follow the manufacturer’s installation instructions. Not following the manufacturer’s instructions could void the home’s warranty or the expose the installer or others to liability issues. The information presented in this article is not intended to replace the installation instructions.

Anchoring Systems for Perimeter Foundation Systems:

To properly anchor manufactured and on-frame modular homes with perimeter foundations, the foundation beams need to be anchored to the foundation AND that the home structural beams need to be fastened to the foundation beams supporting them. This latter part of the anchoring system seems to be most often forgotten or unknown. No one method exists for anchoring the foundation beams to the foundation; but the anchoring method needs to meet these basic criteria:

  • BOTH ends of all foundation beams need to be anchored.
  • If the foundation beam ends are not located in pockets that are tight enough to prevent twisting of the beams, both sides of each end of the foundation beams need to be anchored or the full widths of the beams have to be anchored (as shown in the example photos later in this article).
  • The anchors have to prevent the foundation beams from being pulled laterally out of the pockets or off the pilasters, as could happen if the foundation wall moves outward.
  • The anchors have to prevent the foundation beams from being pushed sideways off of the pilasters.
  • The anchors or the foundation pockets have to prevent the ends of the foundation beams from being lifted vertically off of the pilasters or within the pockets.

Manufactured and on-frame modular homes installed on poured concrete foundations have more anchoring options than concrete block foundations because anchors for the latter need to be tied to the reinforcement in the concrete-filled blocks in the foundation. The following photos show examples of a variety of anchoring methods that I have found during inspections of manufactured homes with foundation beams.

The photo below shows the end of a foundation beam on top of a pilaster. By far the most common method for anchoring foundation beams to concrete block foundations is using the rebar installed to reinforce the pilaster. As shown, the rebar is extended above the pilaster, and bent over onto and welded to the beam, as shown in the photo. This photo shows the preferred method for attaching the rebar to the beam in that the rebar ends are kept short and at least 2 inches of the rebar is welded solidly to the beam. A similar rebar anchor is on the other side of the beam to prevent the beam from moving sideways on the pilaster. Both sides of each rebar end should be welded to each beam.

The photo below shows another variation of rebar anchor that is acceptable, although not as ideal as the previous photo. In this installation, a similar rebar anchor was installed on the other side of the beam. This anchor would be more ideal if the area around the base of the rebar inside the block were mortared to stiffen the rebar.

The photo below shows another rebar/beam anchor that is not acceptable. As this photo shows, the rebar is much longer than in the previous two photos, which allows the rebar to be bent more easily. However, the longer rebar means that the beam is not restrained from excessive movement. Furthermore, only the very end of the rebar is welded, which could allow the rebar to break loose if the beam moved. A closer pocket around the beam would prevent the beam from moving sideways. Additionally, the rebar on both sides of the beam should be shortened and at least 2 inches of both sides of the rebar should be welded to the beam.

A common issue with the rebar anchor is that the rebar does not get welded properly to the beam, as shown in the photo below. As can be seen in the photo, a gap is present between the end of the rebar and the beam flange even though an attempt was made to weld the rebar to the beam. For this installation, the installer only tack-welded the ends of the rebar to the beam and the rebar pulled loose in several places. If the end of the rod had been more solidly welded, the rebar would likely not have pulled loose. However, as with the previous photo, the rebar should have been shortened first and welded closer to the end of the beam.

As the photo below shows, not all uses of rebar as an anchor are acceptable. In this installation, the rebar attaching the foundation beam to the footer (orange arrow) would not constrain movement of the foundation beam and would therefore not be an acceptable anchor. This photo also shows another issue with the pilaster blocks. In this installation, the gaps in the mortar show that the blocks were not fully mortared, filled with concrete or reinforced with rebar. At least, this installer used a sold 4-inch concrete block on top of the pilaster to properly transfer the beam load fully across the pilaster.

As stated previously, poured concrete foundations offer additional anchoring options as shown in the following photos:

The two photos above show variations of the same type of anchor, except one was installed over the top of the foundation beam and the other under the foundation beam. Both photos show that the anchor is bolted to the foundation and both are wider than the beam flanges. The foundation beams need to be welded fully to the anchors, as can be seen clearly in the above photo. Even if the anchor is installed above the beam, welding is needed to restrict the beam from being pulled out of the pocket. Note also that the beam pockets in both photos are just wide enough to accommodate the beam, which helps prevent beam twist. However, these types of anchors should also help prevent twist.

The photo below shows a clever use of the tie-down straps normally used to anchor homes on pier foundation systems. In this case, the straps used to fasten the home structural beams to a concrete footing or pad have been used to anchor this home’s structural beams the foundation. Further, the strap has been properly looped around the carriage beam according to the manufacturer’s instructions, which firmly secures the strap buckle to the home structural beam. The additional strap between the carriage beam and the end foundation wall should not be needed because the home structural beam’s movement is constrained by the foundation and other anchors. If the manufacturer’s installation instructions require this strap to be installed, it needs to be installed to prevent voiding warranties. Technically, this installation does not meet the overall guidelines stated earlier because the foundation beams have not been anchored to the foundation or the structural beams have not been fastened to the foundation beams. However, this installation is at least as secure as homes built on pier foundations. Note also that this photo shows an example of an installation with the foundation beam iinstalled near the end of the home strutctural beam instead of a pilaster, pier or column.

In some cases, concrete block is sometimes installed on top of a poured concrete foundation. This kind of change can happen if additional headroom in a basement was desired after the concrete foundation has already been poured. The photo below shows the way one installer, almost acceptably resolved this issue. The installer built pockets in the block for the beams and then constructed angles to anchor the beams to the foundation. While the installer welded the angles to the structural beams, he did not bolt the angles to the foundation, which made this installation not acceptable. The installer also did not fill the blocks surrounding the foundation beams with concrete and install rebar in the concrete to reinforce the block. Additionally, the rebar in the block needs to be anchored into the concrete of the lower part of the foundation.

Up to this point, I have discussed construction of the foundation and anchoring of the foundation beams to the foundation. To complete a proper anchoring system for foundation beam systems, the home structural beams need to be fastened to the foundation beams. Manufacturer installation instructions that I have reviewed require that the structural beams be fastened to the foundation beams at ALL points where they cross. Manufacturers usually allow two fastening methods, either a 1/4″-inch fillet weld or bolting. An example of welding is shown in the following top photo and bolting in the following bottom next two photos.

By far, welding is usually more expedient than bolting and more secure. Before using bolts, installers should check with the manufacturer to assure that drilling holes in the home structural beams will not void the home’s warranty. If bolting is allowed, installers should also check for manufacturer’s torque requirements for the bolts. Welding installation instructions usually require that both sides of either the home structural or foundation beam be welded; but installers should follow the manufacturer’s specific instructions for the home. Installation instructions also normally require that each joint be fully welded across the full width of the structural or foundation beam, as shown in the top photo above. A number of installers us a weld of only 1 or 2 inches, which is normally not acceptable. Alternative methods of fastening the two beams together may exist; but the installer should check with the manufacturer for acceptability. Local building codes should also be checked for requirements for fastening the beams together.

Earlier in this article, I stated that shims are normally installed between the foundation beams and home structural beams rather than between the foundation beams and the foundation. Wood shims, as shown in the top photo below, are not acceptable because they may not support the load and they do not allow proper fastening of the foundation beams to the home structural beams. When the joints between the foundation beams and home structural beams are welded, metal shims need to be installed between the two beams where needed. Additionally, when shimmed joints are welded, the joint needs to be fully welded so that the shims are included in the weld, as shown in the bottom photo below.

Alternative Foundation Systems and Anchoring Methods:

Previously, I mentioned a second general type of manufactured and modular home construction that is supported directly on the perimeter foundations without need for foundation beams. The marriage line of these homes are usually supported on steel columns or concrete block piers. A load-bearing wall could also be used instead of columns; but, the homes I have inspected that had frame walls built under the marriage line also usually had steel columns. (Again, consult the manufacturer’s installation instructions or hire a licensed engineer or architect to verify the construction is acceptable if the home foundation system deviates from the manufacturer’s instructions.) From the underside, these homes look very similar to site-built homes, as can be seen in the photos below. The first two photos are manufactured homes and the last photo is a modular home:

Note in the previous three photos that the marriage line is the equivalent of the main beam for a site-built home, except one-half of the marriage line “beam” belongs to each side of the home. These homes come in a variety of constructions, and manufacturers are likely to make changes in the future to make the homes look even more like site-built homes.

Besides differences in the marriage line for these homes compared to the homes that have foundation beams, these homes are anchored around the perimeter to a sole plate that sits on top of the foundation. To fully anchor these homes, the sole plate must be anchored to the foundation AND the home needs to be anchored to the sole plate.

Two methods for anchoring the sole plate are shown in the following two photos. The top photo shows a sole plate that has been fastened to an anchor installed in the foundation similar to methods used for site-built homes. The bottom photo shows a sole plate attached to the foundation using metal straps imbedded in the foundation. Some installers have also used concrete anchors and bolts to fasten the sole plate to the foundation. Local or state building codes, the International Building Code or the manufacturer instructions should be consulted to determine acceptable methods for how the sole plate is fastened to the foundation. Keep in mind that the weaker the fastening method, the more anchors might be needed. For example, I would expect fewer anchors being needed for the anchor bolt fasteners in the top photo than for the strap anchors in the bottom photo.

I have observed two variations in home construction that determine how the home is anchored to the sole plate. For homes with wood joists, the wood joists can be fastened to the sole plate directly, as shown in the photo below. In the installation, the sole plate was oversized and lag screws were used to screw joists to the sole plate.

Homes with steel joists may have a sole plate attached to the bottom of the joists, as shown in the photo below. As can be seen in this photo, this sole plate is then screwed to the foundation sole plate.

Some homes have rim joists that extend below the floor joists, which can be seen in the photo above. For these homes, the rim joist can be fastened to the sole plate from the exterior side of the rim joist prior to siding being installed. On the other hand, some manufacturers extend the exterior sheathing below the floor level and attach the joists to the sheathing, which appears to be the case in the photo above where a strap anchor has been used. Manufacturers may have specified methods for anchoring the home in the installation instructions. If the instructions do not specify an anchoring method, refer to local or state building codes or contact the manufacturer or a licensed engineer or architect for recommendations.

Although manufacturers might allow anchoring the home using the rim joist or exterior sheathing, I do not favor this method of anchoring. One major issue with this anchoring method is that the a gap is left between the exterior sheathing or rim joist and the sole plate because of an error or inaccuracy in the construction. This gap could be sizeable. For one home I inspected, a gap of nearly 1 inch was present in some places around the home’s perimeter. The strength in this anchoring method comes mainly from the contact between the sheathing or rim joist and sole plate woods when the fastener pulls them together. If a gap is present, the fasteners takes all of the load, which weakens the anchor. Additionally, verifying whether the home has been properly anchored is difficult to impossible one the siding has been installed. Due to the number of issues with this method of anchoring the home, I recommend that an alternate method that anchors the home’s joists to the sole plate be used.

The Wrap:

I have tried to be as thorough as possible in writing this article; however, I have likely missed some important points. Further, manufacturers periodically change designs that could change installation requirements. Further, so much variation exists currently in home designs that a particular home’s foundation system and anchoring method may be different than presented in this article, but still be acceptable.

Another important point is that recent HUD rules require states to develop installation rules based on the minimum standards listed near the beginning of this article. HUD further required that new manufactured home sets be inspected according to each state’s rules. For installations not covered in the model and state rules, such as perimeter foundation systems, HUD rules and likely many state rules defer to the manufacturer’s installation instructions or a licensed engineer or architect designs. If other state rules are similar to those in Ohio, this information must be obtained prior to obtaining a permit to begin construction. Make sure you are aware of your state’s requirements so that a potentially stiff fine or reconstruction costs are avoided.

Please be sure to contact us with questions or comments or to request a PDF version of this article. I hope to revise this article based on those comments and questions.

Take note: ALL new manufactured home installations in Ohio MUST be inspected

September 23, 2010

I am a certified inspector for the Ohio Manufactured Home Commission (OMHC).  About every month, the Commission meets to discuss issues that arrive relative to the installation requirements for manufactured homes.  At the meeting this month, the Commission discussed the fact that a large number of manufactured home owners are still unaware that manufactured home inspections have been required since September 2007.  Therefore, I thought that this would be a good subject to blog about.

Prior to initiation of the OMHC, the Department of Housing and Urban Development (HUD), powered by the manufactured home industry, developed rules to serve as a model code for all of the states.  The law that passed also dictated that all states would have to initiate a program for inspecting all new installations (sets) of manufactured homes.  At the least, the states had to use the HUD model code as a minimum code for each state.  Ohio adopted a slightly stricter version of the HUD model code, and at times various revisions to the Ohio code are made.

The basic fact is that the Ohio code requires all new installations of manufactured homes undergo inspections.  “New installations” does not mean installations of just new manufactured homes.  It means all manufactured homes, whether they are installed on private property or in manufactured home parks or whether they are brand new or years old.  Even if you are relocating the home from one manufactured home park to another, you must have its installation inspected.  Even if you are relocating a home from private land to a manufactured home park or vice versa, you must have it inspected.

Installations currently require three inspections: footing, electrical safety and final installation.  The footing inspection may not be needed if approval is given to an existing footing that is being reused.  Furthermore, all installations must receive a permit prior to any work beginning.  For information on the permits, the permit application forms and the steps you need to go through in the installation process, refer to this location: http://www.omhc.ohio.gov/Consumers/tabid/59/Default.aspx.  The permit is issued by the same certified OMHC inspectors that perform the inspections.  Local building departments and some Ohio Department of Health agencies perform manufactured home inspections as well as Third Party Agencies, such as my firm, Criterium-Cincinnati Engineers.  You can find a list of Third Party Agency  inspectors by county at this location:  http://www.omhc.ohio.gov/CallforInspections/tabid/57/Default.aspx.   Note that you can be fined if you begin work without obtaining a proper permit.

The rules require that installers licensed by the OMHC perform both the footing and installation work.  Most installers have unlicensed assistants helping them.  In these cases, the licensed installer must be on-site 80% of the time supervising the work.  Installers may also obtain the permit and line up the inspection agency.

After a home passes its inspections, the inspector will place a seal inside the electrical panel.  Note that this seal is only for that home’s installation on the site for which the seal was issued.  If the home is moved to another location, it will need to undergo the permitting and inspection process again and receive a new seal for the new location.

Several other important points need to be understood:

  • If a home was installed  after September 2007, it must still be inspected and meet the existing rules.
  • Homeowners may do their own installations; however, if a homeowner chooses to do the work, he or she is required to do all of the work him or herself, including obtaining a permit.  We highly recommend that homeowners not do their own installations because we have had nothing but bad experiences when they do.  In pretty much all cases, the homeowner is taking on much more work than they realize and likely does not have the proper equipment to do a complete installation.  Homeowner who are thinking about doing the work themselves should review the rules to which the home’s installation must adhere at this location:  http://www.omhc.ohio.gov/LawsandRules/tabid/66/Default.aspx (if you looked, yep, every one of ’em).  Whereas, most installers have had a number of years of experience.  They are also required to be trained and pass a qualifying test prior to obtaining a license.  We therefore recommend that homeowners have licensed installers do the installation.
  • We recommend that the homeowner have the installer obtain the proper permits.  If the installer obtains the permit, he or she is responsible for completing the work.  If the homeowner obtains the permit, he or she is responsible.  If additional work is needed for the home to pass inspection, having the installer responsible for the permit gives the homeowner leverage to assure the work gets done.
  • On the other hand, we recommend that the homeowner select the inspection agency.  Some installers have a “comfortable” relationship with some inspectors and, let’s just say, the homeowner might not be getting the inspection they should.
  • Permits are for 180 days only, which should be adequate time for the installation to occur.  An extension can be given; but, if one is needed, then something is definitely wrong.
  • The homeowner is not supposed to occupy the home until it receives a passing final inspection and is sealed.  The inspector can issue a temporary occupancy permit if he or she finds that the issues that need to be resolved for the home to pass inspection are not serious.  However, the temporary permit, as the name implies, means that the home must eventually pass inspection.
  • Most electrical companies will not connect the electric service to a home until after it passes the electrical safety inspection.  The problem has been that some homeowners have gotten the electrical service connected and then not completed the installation so that it passes inspection.  The Commission is currently working to close this loophole.  Inspectors are also going to get more aggressive at assuring that the installation is satisfactorily completed.

I have heard all of the excuses about why manufactured homes should not be inspected and complaints about the inspection requirements.  But, after performing nearly 600 manufactured home FHA inspections, I understand the requirements for every part of the rules.  The inspections are not intended to simply aggravate the homeowner.  They are there to assure that the home is installed safely and to help preserve the homeowner’s investment.  With proper installation, a manufactured home can last for many years.  I see no reason why a properly installed and cared for home cannot increase in value over time.

Water that foundation

September 18, 2010

Well, I don’t mean literally.  Actually, I mean that sometimes homeowners need to water the soil around the foundation.  Here in the Cincinnati area, as with many other areas, we experienced a very wet spring.  Then, Mom Nature, apparently fearing that she might mess up the averages, pretty much completely shut off the valve.  We are now nearly 6 inches below average on rain–and our clayey soil is rock-hard dry.

One of the characteristics of clay soil is that it shrinks significantly when it dries.  You might have noticed such shrinkage in the gap that has opened between your foundation and the soil.  Keeping the soil evenly moist around the foundation helps prevent or even prevent shrinkage.  However, when watering the soil, don’t just water a narrow band of soil.  I normally recommend watering a band of about 6 feet.  Now, 6 feet is not a magical width; I just mean to water a wide enough band.  If you water too narrow a band or soil, the surrounding ground will suck up the water rapidly, essentially countering your good intentions.  You should also not spray water directly on the foundation, which is never a good practice.

How much to water depends on the soil composition, type and conditions.  Checking the soil using the old finger probe similar to the way you would check the soil in a planted pot is possible.  You just push your finger into the soil to a depth of about an inch and, if the soil feels damp to your finger, it is probably wet enough.  Then again, not being able to push your finger into the soil probably also tells you that the soil is too dry.  You can also use the simple plant moisture meters available in many stores for use on potted house plants.  If you want to get real sophisticated, soil moisture sensors that actuate an irrigation system are also available.  You can find these by Googling “irrigation soil moisture sensors”.  Creative homeowners who don’t want or can’t have an irrigation system installed around their foundations should be able to make up a system using soaker hose, the moisture sensor and control system and an irrigation valve.

So, what is the big deal about the soil being too dry around the foundation.  (Truth is, maybe I should not even be telling you this preventive measure because in the past, we have had a lot of jobs from homeowners because of this issue.  But, that is not our way.)  First and foremost, the foundation can settle and develop cracks and some of these cracks can be severe.  The most common reason for cracks is that the foundation settles unevenly, which is a particular problem with the type of foundation that everyone wants nowadays–the walk-out basement.  Heck, I like ’em too, even though I don’t have one.  With these types of foundations, the soil may be dry to the same depth all around the foundation; but the soil around one part of the foundation may be dry to below the depth of the footing while the soil around another part of the foundation is not.  Dry soil shrinks; so some of the soil around the foundation shrinks while it doesn’t around the other parts.  This condition results in part of the foundation moving while part of it doesn’t.  And that difference in movement can result in cracks.

Besides walk-out basement foundations, stair-step and concrete block foundations (both of which may also be a walk-out basement foundations) are especially prone to developing cracks under uneven soil drying conditions.  Another susceptible foundation construction, which is VERY common, is the crawlspace, stem wall or porch foundation that is poured continuous with, but which is much shallower than, a basement foundation.   The same logic can be used to explain why cracks could develop.  The shallower foundation settles while the basement foundation doesn’t.  Basement foundations that are not walk-out types, stem wall and crawlspace foundations aren’t totally immune from developing cracks either.  The conditions dictate the development.

Slab on grade foundations are also susceptible to developing cracks in the slab, depending on the slab construction.  In the case of these slabs, the soil around the outer edges of the slab could dry while the soil farther under the slab dries slower.  In this case, the soil around the perimeter of the slab shrinks while the soil farther under the slab doesn’t.  The perimeter of the slab settles, while the parts farther under the slab do not.  In this case, the slab might develop cracks as well as heave.

The second reason is that what does down might need to come back up.  Just as clayey soils shrink when they dry, they re-expand when they moisten.  If the foundation settles due to dry, shrinking soil, the foundation might not move back the same way when the soil moistens and re-expands.  In moving back with the expanding soil, the differences in the amount of movement around the foundation could occur, creating stresses that cause cracks.  The soil also might have shifted and exerts pressure on the foundation differently than before.  Soil that shrinks may not re-expand as much as it shrank because the spaces between the soil particles are squeezed reduced as it shrinks.  When the soil re-expands, the spaces between the soil particles might not be the same as before, causing stresses that create cracks.

A third reason for keeping the soil around the foundation evenly moist is one I hinted at earlier in this post.  The gap between the soil and the foundation becomes a water channel when it finally rains.  This issue is a problem mainly for basement foundations.  Don’t let anyone kid you, nearly all foundations are porous to a varying degrees, even those with some exterior water barrier coatings.  Water running down the foundation wall is absorbed by the foundation materials and transferred to the inside of the foundation.  If the foundation happens to have a crack in the right place, the water will have an open path through the foundation wall.

Water that isn’t absorbed by the foundation materials or doesn’t flow through cracks can cause issues around the foundation by eroding soil around the foundation.  In most areas, building codes now require that homes have a foundation drainage system.  Those systems work to capture a great deal of water around the foundation IF they are installed properly.  On the other hand, water has a mind of its own and seeks the path of least resistance.  Therefore, the water might choose to flow under the foundation and not into the foundation drainage system.  If enough of it travels through one area, soil erosion can occur, causing the whole uneven foundation support thing, which can case cracks, and/or worse shifting, of the foundation.

A final, not so directly an issue, is loss of vegetation around the foundation.  In particular for homes built on hillsides, loss of vegetation could result in loss of soil erosion control.  With soil erosion could come soil sliding.  Cracks in dry soil could also open channels to deeper soil layers that are not as well bound together as the upper layers, resulting in slides.

A couple of other things should also be kept in mind.  The foundation may not the only thing that has moved when it settled.  Everything sitting on the foundation might have also moved.  Foundation movement might be imperceptible but still be enough to cause cracks in other interior and exterior building materials. Further, movement is greater higher up in the building, which means that cracks might be found in upper floor materials without be found in lower floor materials.

Another thing to keep in mind is that movement creates stresses in the foundation and other building materials.  Those stresses might not cause cracks right away.  Those stresses could still be present only to cause cracks later on, such as when another condition creates additional stresses—the old straw-camelback syndrome.

I have thrown a lot at you in this post—and without pictures.  (Over time, I promise more pictures.)  The issues can be complex.  Still, they do not mean you need a structural engineer to look at every crack.  If you have doubts, then hire an engineer to check things out and hopefully provide assurance.  On the other hand, you might try keeping the soil around the foundation evenly moist and avoid having the need for an engineer.

It’s just an ABS pad, right?

November 24, 2009

This past week, the Ohio Manufactured Home Commission held a hearing on revised changes to Ohio Rule 4781.  This law is the one that dictates among other things how manufactured homes are installed in the State of Ohio.  If you install any manufactured home in Ohio, whether you are moving the home from one place to another or purchasing it new, or whether it is being installed in a manufactured home park or on private property, this law is the one that the installers and inspectors must follow when installing it.  Interestingly, most manufactured home owners are not even aware of it–until they move the home and try to have the power hooked up.  That is when the power company is going to ask for proof of the required inspections.

The changes in the rule were initiated to align it with the federal Housing and Urban Development (HUD) model codes, which dictated the minimum requirements for all states’ laws.  Ohio initially developed its rule before HUD finalized its model code, by more than a year.  However, when HUD’s model code was passed into law, Ohio needed to align its rules with HUD’s, and that was the purpose of the hearing.

One particular part of the rule change had me concerned.  It was the part where acrylonitrile butadiene styrene (ABS) pads were going to be allowed for all installations in place of a concrete footing required in the current rule.  The foundations of many manufactured homes differs from stick-built homes in that the home is supported on a series of piers as opposed to a wall foundation.  Typical manufactured homes have a pair of steel I-beams running the length of each section of the building.  When set, these beams will sit atop the piers, which are spaced about eight to ten feet apart.  Some manufactured homes do have foundation wall structural systems.  But, even these homes have a series of piers under the home in places.

Piers supporting a manufactured home are usually constructed with some kind of footing and a stack of concrete and wood blocks.  Until now, footings were a minimum of 6″ of concrete and usually were constructed in strips that either ran the length of the home or across the width of the home.  These footings were also required to be at frost depth, which is 30″ in our area.  Additionally, footings that are installed for concrete block perimeter walls for homes that have them are tied together with strip footings that run across the home’s width.  Tieing all of the footings together makes for a very solid foundation base.

The proposed rule change would allow ABS pads to be used in place of concrete footings for ALL installations.  So, what is an ABS pad.  They are a square or oval ABS plastic pad, that is about 1/2″ thick.  The dimensions of the pad that is used depends on how much weight the soil can bear.  Whereas, with concrete footings, a trench needs to be excavated, forms possibly installed and the soil compacted, ABS pad only require the lot to be cleared of debris and vegetation, reasonably leveled, soil compacted if needed and then piers erected.  Do these two installation even sound equivalent?

We at Criterium-Cincinnati Engineers did not think so.  In fact, we know so based on inspections of over 500 manufactured home installations that are qualifying for FHA loans.  These were homes with all kinds of foundation systems, on all kinds of soil types, in many different topographies and both single and double-wide structures.   I was there to try to persuade the cognizant Commission to leave the rule the way it was with NO ABS pads allowed.  Our conviction was that allowing ABS pads was not good for home owners who would not know otherwise.

Although I could not find any logical explanations for why the pads were being allowed, I have heard over and again the term affordable housing.  But, is housing affordable if the structural system fails due to the foundation sinking into the soil?  When this happens, the homeowner could either lose his or her investment in the home or incur large expense to fix the home.  In our opinion, affordable housing should be sensible affordable housing.

Surprisingly, I was the only one to testify against the ABS pads.  With the support of a couple of Commission members, who surprisingly are installers, the Commission voted to at least not allow pads to be used for all multiple section homes unless they are being temporarily set.  ABS pads will still be allowed for single-wide homes, not matter whether they are installed in parks or on private property.  We did not get a full victory; but I am happy with the result.  Multi-section homes are those purchased for long-term housing where the homeowner expects the property to gain in value.  Once set, these homes will likely not be moved, whereas single-wide homes often get moved.

And that is where the rule is at.  I, once again solely, applauded the Commission after the vote for their good work.


%d bloggers like this: