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.