moisture in crawl space - navigating my options

12 years ago

I have a home built in (very humid!) Atlanta in 1950, and expanded in 1970, so it's on two dirt crawl spaces. We're having issues with moisture in one specific area of the newer crawl that shows up after heavy rains - we notice because of a strong muddy smell (and sometimes a mildew-y smell follows that). We've gone under to look when the smell is there, and there is moisture that seems to be coming through the brick. We've never seen puddles of standing water, but there is mud splashed on the walls, so that suggests we may have had some puddles in the past. The ground on the outside of the house in that area is shady, and tends to hold moisture (there is moss growing there) but it slopes away from the house. We have gutters that we haven't always done a great job of keeping clear.

The older crawl does not have a vapor barrier at all, and is powder dry. The newer crawl has a 6 mil vapor barrier, but it doesn't cover all of the ground. There are vents for both crawls that are just open year round, covered with mesh - I don't think they can be closed. We have a new, expensive HVAC unit installed in the older crawl. There's no insulation under our house at all (sometimes I can see sunlight through the floorboards near the vents!), but I think that's a whole 'nother issue.

We've had 6 different companies come out to look, and each has a very different answer for us, at very different price points. I think we've got a consensus that this isn't a major foundation issue, and that while there is some mold and mildew in the crawl, that it's minor and isn't going to require any real remediation effort.

The options that are seeming the most sensible (er, cheapest) to us are to either:

option from contractor 1 - install a french drain to lead water away from the problem area, and then install a 6 mil vapor barrier in on the ground only in the crawl, and leave the brick uncovered. (cheapest quote)

option from contractor 2 - lay a thicker (12 mil) vapor barrier on the ground in the crawl, and run a thinner (10mil) vapor barrier up the brick, so that the entire crawl is covered up to the wood beams. (second cheapest quote)

But we've also had a contractor tell us we don't have a problem at all, one suggest we need a dehumidifier / air exchange system installed, one suggest we need total crawl space encapsulation, and one suggest we need $20k of foundation repair. No one seems to be on the same page about what to do! And I'm out of contractor referrals, and the internet is failing me.

Anyone dealt with this kind of thing, or know anything about it, or know where I could turn for advice?

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Comments (5)

brickeyee
12 years ago
You can ventilate to allow water vapor from the bare earth to escape, or you can try to cover the bare earth to prevent water vapor from entering the crawl space in the first place.

If you place a vapor barrier on the bare earth and fasten it to the walls you can keep water vapor from the crawl space.

Wood battens on the walls with a butyl caulk seal to the wall and fastening the barrier to the wood battens will exclude most water vapor.
SpringtimeHomes
12 years ago
I tend to agree with brickyee and contractor 2. This will yield the best year round indoor air quality. You could probably seal your vents up with this approach.

It may not solve your bulk water problem in heavy rains though. It would be nice to get the french drain as well, if its done right and fixes the bulk water problem.
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Try www.buildingscience.com/ for information about vapor barriers. Another good source for local building advice might be your state land grant university. I do not know anything about your floor finish. I guess you will cringe when I mention pre-finished flooring, but keep reading ;-) The spaces between the boards lets moisture through. With finished in place floors (poly finishes) you have a good vapor barrier. I guess that you understand the "sandwich" prohibition now. If you have a vented crawl space, off gassing will primarily be through the crawl. Ignition is a good question. I am afraid that I do not know much about fire and foam. I know that it burns and that crawl spaces raise fire insurance so it is a good thing to look into. Any kind of covering over the underside of your floor is going to increase the risk undiscovered or delayed discovery of rodent and insect damage. That includes batts, foam or boxing-in with rigid insulation. I do not know if there is any hard information about the relative risks of each method. The rigid insulation alternative is not one that has been addressed in this thread yet. It would be less expensive than foam, if DIY, but it is a lot of work. It has to be taped very well. You could take a hybrid approach and cover selected areas with foam board -- under the most troublesome plumbing areas for example. When you get done with that, you foam the rest. Low density foam pulls out pretty easily. I do not know about high density. You would just have to spray some more in after you make repairs. The problem would be finding the stuff that you need to fix. I would considerer tagging stuff before foaming if it will be covered by foam. You could use durable plastic tags in some color code. If you have a leak, water will run right through low-density foam. I do not think that is so with high-density foam. One important feature of spray foam is the air-sealing capacity. Batts will not do that. That is the problem with it where I live in the humid Gulf South. Air gets around batts even when freshly-installed. It is even worse when it sags. Humid air hits the cool floor, water condenses and does not dry well. Floor rot happens. Even with the best batt installation, the joists become the coolest thing under the house. Condensation happens there and then rot happens. These things worked great before AC existed, but not anymore.
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My house is fairly old and crawl spaces must have been “the thing” when my house was built. All of my neighbors have them too. You dont see any basements in my neck of the woods and houses built on slabs seem to be below a certain price point. You do see some houses built up with open parking underneath (like typical beach houses)- this is more expensive buy perhaps a better idea than a crawl space. For those of you that suggested a dehumidifier- can anyone suggest a brand? I mentioned this to my insect contractor and he said it wouldnt work because the dust and dirt would clog abd break the machine (Im really starting to doubt his advice anyway). I would like to redo the plastic sheeting down there and add a dehumidifier. Any ideas on cost range of this? We have a 2 story, 4500 square foot home. Im reading mixed information about whether to open the crawl space vents. Can someone comment on this?
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daburke
12 years ago
I just did this in my crawl space here in New England. This was a real DYI project since I am not handy. My contractor estimate was $5,200. I did it myself for $475.00. First remove all insulation and replace with new since it may be moist and not effective. I then ran construction foam board ( used on new exterior houses) horizontially along the walls of the crawl space. I attached them to the wall using "Good Stuff" the insulating foam in the can. I sprayed some between the foam board and wall and it's still attached. Then I applied 6 mil poly to the floor and up the sides of the walls ( now covered by foam board) for about six-eight inchs. THE KEY IS TO PREVENT ANY AND ALL MOISTURE FROM COMING UP THROUGH THE DIRT FLOOR. So you can leave / go over the exsisting poly. When done with laying the poly, where it met the walls I again sprayed "Good Stuff" where the floor met the wall still leaving the excess up the wall. When it dries to the poly, wall and floor you have a Tight seal. The worst part was working in the crawl space. Grab an old pillow or cushion for your knee's. Knee pads didn't work for me.
Also a dehumidifier works on a "closed area prinsible" If the vents are open, it will just take the moisture out of the exteriior air. GOOD LUCK
ionized_gw
12 years ago
You have to get rid of the water that runs under there, no question about that. That said, in a hot-humid environment in a home with cooling, the air can be a much greater source of water than the ground below a house. If the floor temperature is below the dew point of the air, you will get condensation. In older raised homes without cooling, there was no problem. Add air conditioning to these old homes, and you get a very high potential for condensation. If the air conditioning is conventional ducted, condensation can happen in very strange places where air is sucked into the structure by the AC blower.

Builders and building code experts have been slow to come around to recognizing that a better solution might be to seal the crawl spaces. In an air conditioning environment, this also helps keep the house cool. That said, I donÃ¯Â¿Â½t think that I want to do that with my house unless I air-seal the floor as well. Eventually, I will spray-foam the underside of the house with low density foam. After that is done, however, sealing the crawl will no longer be necessary.

More information can be found at http://www.buildingscience.com.
energy_rater_la
12 years ago
over the summer I had a big project similar to your situation. old home added on to over the years.
hot humid La.
after mastic sealing all the ductwork, return & supply plenums of 3 systems in the crawl space. this was hard pipe
with floor registers..(and you could see the ground around the cut in the floor for the supply boxes)
unwrapped hard pipe mastic sealed, reinsulated with R-8 ductwrap stapled taped and mastic sealed. sealed all the plenum & supplies. all supply boxes. big job.

then we came back with 3" closed cell foam on bottom of floors.

amazing the difference it made. we also foam sealed the attic @ the roofline. oh and home was balloon framed. lots of air movement.

the crawl space is semi enclosed, and vapor barrier is non existant in places. difficut access in some areas.

midways of the job I attended this class put on by LSUagcenter..heres the info they gave us:

http://www.lsuagcenter.com/NR/rdonlyres/D33F711D-DC4B-4E4C-9ED6-A97DCE9DB026/79806/pub3187insulatingraisedfloorsHIGHRES.pdf

best of luck

moisture in crawl space - navigating my options

Comments (5)

brickeyee

SpringtimeHomes

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