Condensation in a manufactured home crawlspace with “ventilation”

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.

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5 Responses to “Condensation in a manufactured home crawlspace with “ventilation””

  1. Rob Says:

    Hey, I bought a home a couple weeks ago and there is condensation exactly like the pics you provided and it has vents like the pictures you have as well, what do you suggest to control the condensation in the crawl space. ? Thanks

  2. Paul Croston Says:

    How do I get rid of it Ty

    • Matt Klein Says:

      Sorry for the delay in responding to your question, Paul. This past week, I once again encountered a crawlspace in which I got soaked by water on the bottom board and steel. That encounter encouraged me to get on a response.

      For both the home mentioned in the blog post and the recent home, condensation on the bottom board and structural metal was the water that soaked me. But that water came from water in the crawlspace and in the air coming into the crawlspace from outdoors. In this area, condensation in crawlspaces can be bad when outdoor temps are low at night and warm rapidly during the day. Heat conduction crawlspace surfaces due to air conditioning also can make surfaces that are cold enough to condense water. So, the condensation is due to elevated water vapor levels in the crawlspace and chilled surfaces. The first place to attack the problem is through lowering the water vapor levels.

      For both of the homes in whose crawlspaces I got soaked, the main issue was water outside the home. Excess water around the home usually means excess water in the crawlspace. For the recent soaker home, it was on a slight downhill slope that directed water toward the front long face of the home. Additionally, the home’s gutter downspouts emptied next to the foundation. For most homes, even stick-built ones, the first place to begin fixing water issues in a crawlspace (or basement) is to fix the water issues around the foundation. In general, the ground around the foundation or perimeter wall should slope away from the foundation or perimeter wall at an angle of about 5 inches per every 10 feet. Depressions in the soil around the home should also be filled in. If the home is on a downhill slope, a swell and/or French (or sometimes called curtain) drain may need to be installed to divert water around the home. Be on the lookout too for cases where a sidewalk or patio can trap water between it and the foundation or perimeter wall.

      For some reason, most manufactured home installers think that dumping downspout water right next to the home is okay. It’s not. We recommend that a drain line be installed to carry this water away from the home. Even a drain line system that carries water about 10 feet away from and about 5 inches downhill of the home can be very beneficial. Pop-up drains on the drain lines help assure that the end of the drain line remains open and doesn’t get chewed up by mowers. But, remember to clean the debris out of them annually.

      If the home is newer and has a permanent perimeter/foundation wall (as opposed to skirting), it should have had a footing drain line installed along the perimeter wall/foundation footing. If older or in an area where no one inspects installations, then the perimeter wall/foundation may not have a footing drain. Installing one along the it could help. A properly installed perimeter drain system could also be useful for skirting. In case you are thinking about it, do NOT connect the downspouts to a footing drain lines. The two can be connected at the take-off lines if installed so that water from one cannot back up into the other.

      Inside the crawlspaces with a dirt or gravel floors, a vapor barrier could help IF it is installed properly. Most aren’t. I kid you not that they are a pain to install after the home is installed. But, one can be installed and installed correctly with time and patience (and a decent clearance between the bottom board and crawlspace floor). The important term here is BARRIER, and that barrier is working against WATER VAPOR, not water. Water vapor behaves like all other gases. Therefore, any openings in the barrier will allow water vapor through. So, all seams in the vapor barrier need to be properly sealed as well as seams between the vapor barrier and the perimeter wall/foundation and vapor barrier and piers. Trust me, sealing is much more difficult than it may sound.

      If the water table is particularly high in the ground under the home, a sump pump system may be needed. I have seen some pretty crazy sump pump installations. (H-m-m-m, maybe that should be another blog topic.) Basically, you should use a preformed sump–and, especially no 5-gallon buckets or pieces of concrete drain line. The hole for the sump needs to be dug deep enough so that the top of the sump is even or just slightly elevated about the ground level. The hole also needs to be dug wide enough for the sump plus about a 6-inch layer of gravel around the sump. Don’t forget to open holes in the sump so that the water can get into the sump. (Yes, I included that warning on purpose. Guess why? Okay, I’ll tell. Ever see a floating dry sump?)

      Finally, if you have done what you can to remove water from the soil under and around the home or to prevent water vapor getting from the soil into the crawlspace air, another option could be a powered vent. A powered vent activates when the humidity levels in the crawlspace are higher than a setting on the fan. This system will help to remove excess water vapor in the crawlspace. It could also help more rapidly warm up the crawlspace and parts of the home to minimize condensation. Since this option not only costs to install but also costs every time it operates, I would use it as the last option.

  3. Rob Says:

    Thanks Matt, the home does not even have gutters installed. So we are going to start there for sure and go step by step to see what is helping. I may have more questions. And thanks for your response. Have you worked on ridding these homes of moisture? Or seen any after effects of someone trying to fix this problem?

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