Archive for the ‘Weather barriers’ Category

Condensation in a manufactured home crawlspace with “ventilation”

April 27, 2011

So, your brand new home was built with a crawlspace that has the vents installed according to code requirements. Further, the crawlspace has a proper vapor barrier covering the floor. You should have absolutely NO concerns about moisture in the crawlspace, right? Well, maybe.

Here is one case where I found out in a rather uncomfortable way that a crawlspace built with proper ventilation and a moisture barrier (of sorts) can indeed get lots of moisture.

One spring day last year, I left a meeting in Columbus around noon and headed toward Wilmington to do an FHA inspection on a new manufactured home installation. This home was built on a crawlspace with a poured concrete slab floor. The home’s air conditioning was not operating because it had not yet been fully installed. Wilmington had received light rain the morning of the inspection. The home reportedly has had drainage problems at one end; but the crawlspace was dry. By the time I got to the home, we were experiencing our usual humid weather our springs and summers bring.

Let’s get into the photo (fun) part of the story.

This photo shows a front view of the home on the day of the inspection. Note the right crawlspace perimeter wall.

This photo shows a closer view of the right perimeter wall area, which was still having some drainage problems on the day of the inspection.

When I went to enter the crawlspace, this view greeted me. Note the water droplets hanging on pretty much every surface in the crawlspace; but the slab is totally dry. BTW, that metal bar angling from the slab to the home’s frame is a lateral brace—part of the home’s anchoring system.

In a view down the crawlspace, water droplets can be seen on pretty much all surfaces.

And since I have a lot of pictures, here is yet another view of the water droplets on surfaces. The lateral brace in the photo is the second of the pair of braces used in the anchoring system. Note all of the droplets on the bottom board (the membrane along the bottom of the home.

This photo shows a closer view of water droplets on bottom board—and by this time on my camera lens.

Yep, a lot of water was present. And every time I raked any of these surfaces, I got a shower of cold water—not a pleasant experience.

This photos shows that the crawlspace vents were wide-open. Interestingly, no surfaces near the vent has water on them.

Where am I going with this story? All of the water droplets seen in these photos are due to condensation. The prior night, the area where the home was installed had colder temperatures and, since the home was not heated, the crawlspace temperatures were also on the chilly side. The next day, as is common in our area, outdoor temperatures climbed rapidly, as did the humidity levels, fueled in part by recent rain. The crawlspace surface temperatures remained below the condensation point of the air, causing water droplets to form on pretty much every surfaces inside the crawlspace, except those near the vents where the surfaces apparently warmed more rapidly.

I believe that this case is proof that even properly ventilated and moisture protected crawlspaces can get water in them. The condensed water may have come from water vapor coming up through the slab. However, the open vents provide a more open path to water vapor in the outside air.

Even if water vapor had come up through the slab, this case shows that the water vapor can be converted back into water droplets that can be absorbed by the crawlspace materials exposed to the water. Thankfully, the intact bottom board of this manufactured home prevented moisture from reaching the insulation above the bottom board. Otherwise, the insulation could sop up the water like a sponge and hold it long enough to possibly cause more serious issues.

However, this case shows that water can get inside a crawlspace without liquid water entering the crawlspace. If surfaces inside the crawlspace are below the dewpoint of air entering the crawlspace, condensation will occur. Having vents in the crawlspace open it up to outside air which can supply the moist air. Open vents can also allow heat in the crawlspace to escape, allowing surfaces in the crawlspace to cool to below the dewpoint temperature of air that may enter the crawlspace later.

Now, if the crawlspace does not have a vapor barrier, moisture issues could be much worse. I am looking forward to the time when I enter a crawlspace that actually has fog—and I have been in some that were close.

Oh, one other lesson I learned is that if you are going to enter a crawlspace with condensation on the surfaces, you will get wet. In this case, I was soaked to my underwear by the time I left the crawlspace. Very unpleasant.

Shingle Overlays—Just Say No Way

March 11, 2011

Eventually, each owner will need to replace the shingles on his/her residence. At that time, the owner will need to decide whether to install new shingles over the existing shingles, known as overlaying, or to strip all of the shingles off to the roof deck before installing the new shingles. For the former, the existing flashings are also normally kept or supplemented. For the latter, flashings are normally replaced, as well as the underlayment. I will state up front that my firm, Criterium-Cincinnati Engineers, does not support overlaying and this blog lays out our reasons.

Building owners usually only give one reason FOR overlaying shingles and that is the cost is less than fully replacing the existing roof components. On the other hand, roofing professionals and engineers have a number of reasons NOT to overlay. These reasons include the following:

  • Total removal of all of the old roof materials allows inspection of the roof deck, valleys, joints between the roof and walls or chimneys, and areas around roof penetrations, such as sanitary or roof vents. This inspection could discover rotted wood, insects, holes and a number of other issues that could compromise the roof. Some might argue that these issues are visible from within the attic. Having been in more than a few attics, I can assure that these issues are not always visible. For some residences, the attic cannot even be entered and in others no attic exists, such as in residences with cathedral ceilings. We believe that a residence’s first roof replacement should particularly not be an overlayment because of the poor quality of some builders.
  • Total removal of the old shingles can assure that an underlayment is installed. Underlayments perform two main functions: an additional water barrier against leaks in the shingles and separation membrane between the shingles and the roof deck. Shingles installed directly on the roof deck sometimes melt or stick to the deck. But, shingles expand and contract on the roof deck as they heat up and cool down. Shingles stuck to the deck are restricted in their movement, which could result in the shingles buckling or tearing, shortening their life or creating leaks.
  • One of the most vulnerable parts of the roofing system is valleys. Valley flashings can fail and more than a few of these flashings have also been installed incorrectly. Poorer quality builders may not have installed valley flashings at all, trusting that the underlayment will protect the valley. Instead, shingles are weaved across the valley. (By the way, Criterium-Cincinnati Engineers does not support weaving shingles over valleys because of the increased chance for leaks.) Replacement, rather than reuse, of the valley flashings helps assure that valleys will be adequately protected. If the roof is older, new techniques have been implemented since the old roof was installed that adds better protection. One such technique used by better quality roofers is to install an elastomeric membrane beneath the flashing. Not only does the membrane protect against rain leaks, it protects against leaks due to ice dams.
  • In some areas of the country, roof areas above eaves are another area that may need extra protection because they are where ice dams tend to develop. These areas are also vulnerable to shingle lifting due to wind. Better quality roofers install an elastomeric membrane as underlayment over this area in addition to the underlayment used on the rest of the roof. Most original roofs do not have this degree of protection.
  • Rakes, the roof area over the gable, are other areas that are exposed to potential lifting. During overlayments, another layer of shingles are laid along the rake, which raises the edge of the shingles where they are better exposed to the wind and lifting.
  • Roof penetrations, such as vent pipes, also need to be flashed to prevent water leaking through the gap between the roof deck and penetrating object. But, these flashings can also fail and are sometimes damaged by high winds. When a roof is overlaid, these flashings are usually not replaced. So, what happens if these flashings fails before the second (or third) roof is replaced? Removal of the flashing could damage the roof shingles. The usual patch is to smear the flashing seams with tar or roof caulk. Tar or caulk does not normally last as long as the roof shingles and will have to be periodically inspected and repaired. If a leak develops in the tar or caulk, the usual (wrong) solution is to apply more tar or caulk, and the new material commonly fails quicker than the previous material. Even if the flashing is replaced, the best place for it is in the first layer of shingles, which is virtually impossible when more than one layer of shingles is installed.
  • Many two-story homes have second-story exterior walls that meet first story roofs. Flashing is supposed to be installed between the wall and the roof to prevent water entering through the gap between the roof deck and wall sheathing. As other internet posters on the subject of overlayments point out, roofers installing overlayments try to reuse the installed flashing by bending and weaving it with the new shingles. Alternatively, they may also pry out the siding, shove new flashing up under the siding and weave that flashing with the new shingles, leaving the old flashing in place. We have also seen where a roofer installed a continuous flashing up under the siding and ran a bead of roofing caulk between that flashing and the new shingles. And we have also seen where new flashing was not installed at all, but the roofer relied on roofing tar to stick the edge of the new shingles to the old ones. None of these alternatives are acceptable, especially if the old flashing leaks.
  • The addition of a new layer of shingles adds considerable weight to the roof structure. A new layer of shingles weighs about 2 pounds per square foot. Although that amount of weight does not seem like a lot, think in terms of 200 pounds for ONE layer of shingles for a 10 foot X 10 foot area (one square). Add the weight of the original layer of shingles and the total weight of the shingles is now at least 400 pounds per square. Over time, this weight can cause rafters to bow or the roof to sag, particularly for roofs with long rafter spans (distances between supports), rafters that lack ties between opposing rafters, or homes with balloon framing. Likewise, some builders use the maximum spacing between rafters with the minimum thickness of roof sheathing allowed by codes. The result is that the deck sags between the rafters causing the waviness sometimes seen in some roofs. If the roof has developed sags between rafters with only one layer of shingles, what do you think the roof will do with two or more layers? Add an abnormal snow load and the roof could collapse, as some folks found out during the 2010-11 winter.
  • As stated, shingles expand and contract as they heat and cool. The degree of shingle expansion and contraction with change in temperature further varies with thickness, material composition, manufacturing method, lot and a number of other factors. If one layer of shingles is expanding and contracting differently than the second layer of shingles, shear stresses can set up in the layer that expands or contracts less, which eventually will cause tears in the shingle. If these tears are exposed to weathering, the shingles life can be shortened. We have observed that many builders install thinner, cheaper shingles as the original roof on many homes. Homeowners, on the other hand, tend to install thicker sculptured shingles as the overlayment because homeowners believe they will get longer life from them. Guess what that usually means? Yep, two different types of shingles with likely different expansion and contraction properties that are also were likely not even made by the same manufacturer. Since the lower layer of shingles are thinner, they can expand and contract more than the overlayment shingles, which results in tears in the overlayment shingles.
  • Multiple layers of shingles add insulation to the roof, which leads to a hotter attic. In turn, a hotter attic leads to the shingles getting hotter. Heat is a major factor in breaking down shingle materials. Further, a hotter attic means greater expansion and movement of the shingles. The result is a shorter shingle life. A hotter attic also means that a homeowner could be paying more for cooling in the summer when the attic heat is transferred into the living space.
  • We have noted many cases of vertical stacking installation of the shingles. Vertical stacking is where the shingles are installed in eave to peak columns rather than installing them diagonally starting at one of the corners over and eave. Although shingles on properly installed roofs can start curling over time, particularly in overly hot attics, the shingles along the sides of the columns of vertically stacked shingles begin to curl more often and quicker than other shingles. The curled shingles make an uneven base for the new shingles, which creates uneven pressure on the new shingles. In turn, the uneven surface can cause tears in the new shingles exposing the inner part of the shingles to weathering, leading to shortened life.
  • Overlayment shingles are very often not aligned horizontally with lower layers. This misalignment results in the mid-area of upper shingles arching over the tab ends of lower shingles—again with the uneven base thing, causing the tears, weathering, etc.
  • Many shingle manufacturers offer a guarantee. However, that guarantee may not apply to overlays.
  • Dark streaking on roofs is usually caused by a very, very hardy blue-green algae. What happens when these shingles are overlaid with new shingles? That question has not been answered; but, the possibility exists for the algae to spread from the old shingles to the new ones.
  • Shingles that are failing begin to hold moisture. One sign of excess moisture is moss growing on the roof. When new shingles are laid over shingles that are holding moisture, that moisture has to go somewhere. If a moisture barrier exists below the roof deck, such as closed cell foam and insulation with a vapor barrier, the moisture could become trapped between the moisture barrier and the shingles, potentially creating a wood rot condition. Speaking of the moss, how sure are you that the roofer has bully removed the moss before installing new shingles? Exactly what happens to the organic matter trapped under the new shingles? Organic matter is also going to be in the old shingles from the moss rhizoids (root-like structures) that have grown into and between the shingles.

Most roofers estimate that useful life of overlayment shingles can be as much as 25% less than their claimed life, which means that overlayment may not cost less in the long run. For sure, if the roof leaks, the cost of repairing the roof and damaged interior finishes could also vaporize any cost savings from overlayment. The bottom line is shingles overlays just might not be worth the expected savings.

What goes out must come in

December 5, 2010

On my Linked In page, I passed on a link to an article titled, “Makeup Air for Range Hoods” (  The author, Martin Holladay, digs into the details of adding a larger range hood to a home.  In particular, he investigated whether consumers were warned about what could be the impact of adding such a hood to a home.  Mr. Holladay’s blog is a fair warning to consumers that they might not be warned about products that could have a negative impact on your home’s environment, and that impact could be hazardous.

In this post, as I promised on my LI page, I am going to dig into more detail about the impact the fan or other devices that change home pressurization could have on the home and potentially its occupants.  Let me start the same way.  Consider your home–or any building for that matter–as a box.  When air is removed from that box, replacement air has to come into the box to replace the air that is removed.  This replacement air is normally called makeup air by building professionals.  The issue is from where that makeup air comes.

If the home is air leaky, makeup air will come through openings in the building’s exterior shell, i.e. walls, roof, windows, doors, etc.  Leaks are usually a major issue because the air can come from many places.  Rehabbing older homes cuts down on the leaks, but usually cannot totally eliminate them.  But, even newer, so-called tight, buildings have air leaks.  The problem with air leaks in all buildings is mainly a thermal comfort issue because leaks cause drafts, and few people enjoy the feeling of a cold air stream inside the home on a cold day.  Another just as important issue is that if air can come in through a leak, it can go out through a leak, which translates into loss of heated or cooled air.  But, air streams flowing past hoods, fireplaces, ventless heaters, etc. can impact their operation.

Air is a lot like most people in that it takes the path of least resistance.  So, air coming through leaks can mess with the home’s return air system.  For a heating and air conditioning system to work properly, adequate air of a certain temperature has to be supplied to an area to compensate for the heat gain or loss from that area.  What may no be known is that air has to also be removed from the area to help the supply air side of the system work right.  In buildings with poor return air systems, large temperature differences could exist from one area to another even if the supply air flow is ideally designed and installed.  What can happen is that air entering through leaks has the path of least resistance to the air handler.  That air, then, prevents the return air system from returning air back to the air handler from some (or all) of the building’s areas.  Those areas that do not have proper air return will be hotter or colder, depending on whether the air handling system is in the cooling or heating mode, respectively.  Alternatively, those areas through which the leak air is traveling could be too hot or too cold.

What about buildings that are pretty well sealed?  If the exhaust fans in the home do not have adequate makeup air, they will either not move as much air as designed or makeup air will come from wherever it can, which might be from undesirable places, such as through flues or chimneys.  The condition of air flowing in the reverse direction from which it is intended is called backdrafting.  When backdrafting occurs in flues and chimneys, combustion gases, including carbon monoxide, could be pulled into the home.  When wood is not being burnt in the fireplace, backdrafting air can pull creosote emissions into the home, which believe me is not a desirable fragrance. Backdrafting can also impact combustion of some appliances, making them less efficient.

What if a combustion appliance, such as a water heater or furnace, have flue booster fans that are supposed to push the exhaust gases outdoors.  If the appliance is a closed system, such as many of the higher efficiency furnaces, no impact should be expected because closed systems pull air directly from outdoors.  Appliances that pull air from the general building air, as do the water heaters with flue fans, may be affected, depending on which fan in the building moves more air or other characteristics.

The impact that exhaust fans could have on other combustion appliances is not unknown to building professionals, though.  Some homes with furnaces that used general home air for combustion have a duct that runs from outdoors to somewhere in the vicinity of the furnace.  That is all.  This duct is not connected to any fans or any other devices.  This duct is simply a path for air to travel from outdoors to indoors to makeup air removed from the home.  Do they work?  Maybe.  But, as I said earlier, air takes the path of least resistance and, if the duct is not the path of least resistance, it will not work.

The concern as stated in the blog post cited at the beginning of this blog in particular was discussing the installation of large kitchen exhaust fans that move over 1000 cubic feet per minute (cfm) of air.  That is an extraordinarily large fan for a home.  Will the usual kitchen exhaust fan cause the same issues?  If it doesn’t exhaust air outdoors, which is normal for these fans, the answer is most likely no.  If the fan exhausts air outdoors, the answer is maybe.  By itself, the fan likely will not cause backdrafting at the least.  That fan in combination with other fans might cause backdrafting.  Again, if the home is air leaky, any exhaust fan can pull air through leaks, causing thermal comfort and/or heating or cooling efficiency issues.

Are exhaust fans the only things that can cause air leakage or backdrafting issues?  Well, no.  All buildings have a chimney effect where heated air rises within the building.  As this air rises, air is pulled into the building at lower levels.  The chimney effect is for the usual home is definitely not as great as that for a high rise building.  In most homes, backdrafting due to the chimney effect is likely not an issue; but the chimney effect can cause drafts in lower parts of the home.  The only way to know whether a backdrafting or draft issue exists is through investigation.  A homeowner might be able to investigate the issue using smoke from an incense stick or other air flow indicator.   However, a professional will know more about the conditions to which to test under and will have more sophisticated instruments than a homeowner.

So, if you have this favorite nook in your home that sometimes feels comfortable and then other times feels drafty, consider that the reason could be an exhaust fan or the home’s air handler pulling air through a leak.  What to do about it from there is up to you.

Home weather barriers, vinyl siding and Hamilton County Ohio

July 29, 2010

In inspecting a home under construction, I recently ran into an issue dealing with a weather-resistant barrier.  This barrier is one that protects exterior wall materials from weather exposure, particularly water.  So, the best place to begin this discussion is by defining what a weather-resistant barrier is.  The American Vinyl Siding Institute states the following on their website:

What Is a Weather Resistant Barrier System? It is a system that includes water shedding materials and water diversion materials. Weather resistant barrier systems commonly consist of a combination of exterior cladding, flashed wall openings and penetrations, weather resistant barrier material, and sheathing. Effective weather resistant barrier systems will shed the water initially, control moisture flow by capillary and diffusion action, and minimize absorption into the wall structure. The level of weather resistance required is determined by the applicable building code and structure.

The 2007 Ohio Building Code, which basically is taken from the 2006 International Building Code, defines a water barrier, which is basically one of the major purposes of a weather resistant barrier, as:

WATER-RESISTIVE BARRIER. A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.

This code further details a weather-resistant barrier as:

1403.1 General. The provisions of this section shall apply to exterior walls, wall coverings and components thereof.

1403.2 Weather protection. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing, as described in Section 1405.3. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with the International Energy Conservation Code.

1404.2 Water-resistive barrier. A minimum of one layer of No.15 asphalt felt, complying with ASTM D 226 for Type 1 felt or other approved materials, shall be attached to the studs or sheathing, with flashing as described in Section 1405.3, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer.

1404.1 General. Materials used for the construction of exterior walls shall comply with the provisions of this section. Materials not prescribed herein shall be permitted, provided that any such alternative has been approved.

1404.2 Water-resistive barrier. A minimum of one layer of No.15 asphalt felt, complying with ASTM D 226 for Type 1 felt or other approved materials, shall be attached to the studs or sheathing, with flashing as described in Section 1405.3, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer.

Section 1405.2 Weather protection. Exterior walls shall provide weather protection for the building. The materials of the minimum nominal thickness specified in Table 1405.2 shall be acceptable as approved weather coverings.

In looking at the home under construction for the first time, I noted that a weather-resistant barrier was not installed on the home.   Most people will recognize a weather-resistant barrier as the usually white paper-like wrap, most commonly with the name Tyvek printed on it in large letters.  Other similar wrap or other materials are also used.  That is where the problems began.

In inquiring about the lack of weather-resistant barrier, I asked for the drawings.  In reviewing the drawings, I noted that no weather-resistant barrier was specified.  When I inquired about why none had been installed, the builder informed me that the Hamilton County, Ohio Building Department did not require it.  Apparently, the building department believes that vinyl siding, which was being installed on this home, was an adequate weather-resistive barrier.

I decided to investigate further on the ultimate authority.  On the internet, I found that the Vinyl Siding Institute states in its Vinyl Siding Installation Manual (

Weather Resistant Barrier

Vinyl siding has always been designed as an exterior cladding, not a weather resistant barrier.  Vinyl siding is designed to allow the material underneath it to breathe; therefore, it is not a watertight covering. Because of its design and application, it provides a supplemental rain screen that enhances the weather resistant barrier system by reducing the amount of water that reaches the underlying weather resistant barrier.

What Is a Weather Resistant Barrier System? It is a system that includes water shedding materials and water diversion materials. Weather resistant barrier systems commonly consist of a combination of exterior cladding, flashed wall openings and penetrations, weather resistant barrier material, and sheathing. Effective weather resistant barrier systems will shed the water initially, control moisture flow by capillary and diffusion action, and minimize absorption into the wall structure. The level of weather resistance required is determined by the applicable building code and structure.

Best Practice: To achieve designed performance, vinyl siding must be installed over a weather resistant barrier system that includes 1) a continuous weather resistant material and 2) properly integrated flashing around all penetrations and where vinyl siding interfaces with other building products such as brick, stone, or stucco. Refer to the manufacturer’s installation manual for specific product applications and recommendations. Whichever product(s) you decide to use as part of a weather resistant barrier system, be certain the materials meet the applicable code by contacting the manufacturer of the weather resistant barrier material(s). Always consult the applicable building code for minimum weather barrier requirements in your area. Keep in mind that additional measures may provide better protection against water intrusion than the minimum requirements of the building code.

The Vinyl Siding Institute clearly states that vinyl siding is not an acceptable weather or water resistant barrier.  Since vinyl siding is not considered to be a weather or water resistant barrier, installing vinyl siding without a proper weather-resistant barrier cannot meet the requirements of the building codes for Hamilton County, as taken from the Ohio Building Code and the International Building Code and cannot be considered as proper building practices.  Furthermore, The Vinyl Siding Institute states that vinyl siding needs to be installed over a weather-resistant barrier, and basically describes the properties of a material such as Tyvek, although it is not the only weather-resistant barrier available.  This Institute further states that proper flashing is required for the siding.

So, am I making much ado about nothing.  I hope not.  Water, especially from wind driven rain can get behind any siding material, but more so vinyl siding.  This water then can reach the underlying wood materials.  The problem areas might not be behind where the water reaches the underlying materials, they usually are where that water flows after landing on the materials.  Water that gets behind the siding will flow down the face of the sheathing to points where it can pool, such as above windows and doors and at the base of walls.  At these points, it can enter into the wall cavity itself if those areas are not properly flashed.  It can also enter through gaps between the sheathing.

Once inside a wall, the water can be absorbed by the insulation.  Insulation holds water really well–nearly as well as a sponge.  If enough water is present, mold will grow because mold spores and their food sources are endemic.  Mold can further cause wood rot.  Other moisture-related damage can also occur, particularly to materials made from oriented strand board (OSB), a very common building material and one that has a bad habit of delaminating when exposed to enough moisture.  Do you think that repairing these materials can be expensive?  You betcha it can, particularly if structural members are involved.

What is the bottom line here?  If you have the abilities to review the construction drawings, do so very carefully and inspect closely for a proper weather-resistant barrier.  If you don’t have this expertise or ability, then hire someone who does, such as a capable architect or engineer.  And remember this point, drawings are best reviewed BEFORE construction begins.  My clients learned that lesson at a cost of $1800, and even then, the weather-resistant barrier was not ideal because the windows and doors were not properly flashed according to the manufacturer’s recommendations.

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