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The house we recently bought has a bit of a mold problem in the crawlspace. We'd like to do something about this before moving in. There seems to be a distinct lack of people who know how to deal with mold. So I thought I'd see what people here have to suggest. The house is a tri-level. The crawlspace is under the living/dining/kitchen wing. It is accessed through a hidden panel in the laundry room. It is about four feet high, with a dirt floor mostly covered with plastic sheeting. The sheeting has many gaps. There is a shallow trench running diagonally across the crawlspace, with two pipes running through it. One is solid metal pipe that is the main sewer connection for the house. The other is a orange masonary pipe, with about half inch gaps between the pipe sections. This presumably connects to the storm drains and the footer pipes around the outside of the house. The gaps in this pipe were once covered by some bits of filter paper, but those are just laying about now. The last ten feet or so of this valley is full of mold. Atmospheric mold spore counts taken in the house run about 20 times the maximum recommended level. We've had some other tests taken here and there, but don't have results back yet. There are only very small amounts of mold anywhere else in the house. Mold needs mosture and something to eat. There are small amounts of mold growing on the basement walls in the laundry room, but none in the basement walls in the crawlspace. This is probably partly because the crawlspace is cooler, thus there is less condensation on the walls, but also because the laundry room walls are painted and the crawlspace walls aren't. Paint is food. So the first question is where the moisture is coming from that is feeding the mold in the valley. I think it was a backup from the storm sewer line. Either water from storm drain or the footer pipes must have flowed into the house at one point. That's why the paper is off the pipe gaps. The other possibility is that water leaks in elsewhere (seapage through the walls or whatever) and collects in the low spot by the pipes. I should check other low spots for mold. If the problem is backflow, then we could simply shut off the drain. This takes a $6 part. But that would leave us without a drain in the crawlspace, which may or may not be a problem. That's one semi-expert's opinion: shut off the drain, maybe apply some kind of fungacide to the existing mold, and fix up the vaper barrier so it covers everything. Another semi-expert favors redoing the drain pipe in some more thorough way, so it functions as a drain, fixing up the vapor barrier, and covering everything with gravel. Both semi-experts are tempted by the idea of just paving the crawlspace with concrete. However the crawlspace has no entrance except the laundry room. You'd have to cut a hole in the basement wall to be able to get cement in, probably. As another problem, the house also has some high radon readings. The unpaved crawlspace floor might be a source for that, so doing something about it may be useful in that way too. Any bright ideas or relevant experience or wild guesses?
10 responses total.
Surely the crawlspace is ventilated to the outside? If not, cut vent holes with louvres to keep out rain. I don't understand how the "drain pipe" is connected - from what to what? Is it to drain the crawlspace? That is the usual reason for just laying loose ceramic drain pipes with tarpaper over the gaps (and then covering all that with gravel). If that's it..why does the crawlspace have to be drained? Where does water enter it?
Definitely restore the vapor barrier. A lot of moisture comes up from the soil.
Moisture from the air also condenses in the crawlspace since it is cooler than the rest of the house. You could continually exhaust crawlspace air if you had a source of dry air. Dehumidify the basement. After putting in a heavy vapor barrier, taped around the edges, try sealing off the crawl space better from the rest of the house to confine the humid air and mold in there. We have extra used dehumidifiers that you can borrow (or keep) to see if this fixes the problem. Our crawlspace, which has an intact taped vapor barried under 4" of concrete is also musty smelling and humid. In the summer air moisture condenses on the basement floor. A test for whether water is coming from condensation from the air or from below is to tape a largish piece of heavy plastic to the floor for a week or so and see which side of it gets wet. Why do you have footer pipes? Are you in a low-lying flat area?
Apparantly the air tests in the crawlspace showed mold spore counts in the
170,000 levels, where around 1000 is the normal high level.
The crawlspace currently has no vents. I'm not sure I easily cut vents. The
floor above the crawlspace isn't more than 8 inches above the level of the
outside ground, so any vent you cut would pretty much be underground. You'd
have to rig some kind of chimney for them.
Here's a slice of the house, cut about four feet underground, at the floor
level of the lower level. The house is a tri-level, with living/dining/
kitchen above the crawlspace wing, and bedrooms above the family room wing.
+-X--------------------------+ - - - - -
front | |
of | |
house | |
| CRAWLSPACE | Screen porch on
| | slab above here
| |
| |
===|=@===\ |
| \\ | - - - - - -
===|=@==\ \\ Sewer |
| \\ \\ line |
| \\ \\ |
| \\ \\ |
| \\ \\ |
| drain \\ \\ Kitchen |
| pipe \\ \\ Drain |
| \\ \\========* |
| ? || +--------+------------------------------+
| ? || | -> |
| |stairs |
- - - - +------------- -+--------+ |
| | 1/2 | family |
| | bath | room |
Garage on slab | +-- -+ |
above here | |
| |
| +--------+---- --------------------|
| | |
| Laundry/ | office |
| furnace | |
| | |
- - - - - - - - - - +---------------+------------------------------+
The sewer line and the storm drain each come into the house at the front.
There are tall vertical pipes there, with caps on the top. I think these
are cleanouts. Once is connected to the main sewer line for the house,
connecting to the kitchen drain and burrowing underground in the direction
of the laundry/bathrooms. The sewer line is a black metal pipe. The
drain pipe is made of orange masonary, and is deliberately laid with 1/2"
gaps between each pipe section. I believe it is intended to act as a drain
for an water that accumulates in the crawlspace. I don't know if the other
end of it goes anywhere. Someone I talked to said that it might connect to
the footer pipe in back of the house (so water collected by the footers in
the back of the house would flow through the basement on the way to the storm
drains (sounds like a really bad idea), but seeing the way it is going, I
don't think so. It ends up going undergound, but I have no idea how much
further it goes than shown, if it does. I suspect probably just ends.
I don't actually know if there are footer pipes, but there usually are on
most houses.
Obviously this drain pipe is not well placed to drain the whole crawlspace,
and there are some other low spots which also appear to have mold in them.
I can see droplets of water on the underside of the vapor barrier in these
spots. So I think if backup is a source of moisture, it isn't the only
source of moisture.
Putting down an airtight vapor barrier would probably help. The mold would
likely continue to grow under the vapor barrier, but it wouldn't be getting
into the air.
I'm leaning more and more toward just paving the thing. We could then take
down the insulation currently stuck to the ceiling, cut a vent into the
heating duct, aand have a heated storage space. We'd need to redo the drain
pipe first. We'd probably lay some pipes for a radon system to use while
we were at it.
Getting concrete into the crawlspace is a bit of a challenge. You'd need
a hole in the basement wall. You can't do it on front, because there is
a porch slab going the full length of the front of the house. At the -X-
there is already an 8" square hole in the wall, blocked off. That might
be big enough to pump concrete through, or it could be enlarged.
If you remove the ceiling insulation in the crawlspace, the house will lose heat into the crawlspace floor unless you put some foam insulation (say 2" of styrofoam) down under the vapor barrier before pouring a concrete floor, and you would probably also want to insulate the crawlspace walls to keep them warmer. Without insulation, not only would you waste a lot of heat, but you would get condensation when warm air from the house (which holds more moisture) goes into the crawlspace and condenses on the cooler floor and walls. And this would grow lots of mold which would get into the air which circulates around the house in the heating system. I still think you are better off to make sure the crawlspace is sealed off well from the house after you have put down a good vapor barrier to keep it a bit dryer. You also would not want to store things on an uninsulated crawlspace floor because they would get damp on the bottoms and rot, rust, or mildew. Attics are much better for storing most things, or separate storage sheds, which you can buy for a few hundred dollars in kit form (metal sheds, or plywood - try Sears).
Put vapor barrier under the concrete. Concrete craks with time.
Concrete also is not a vapor barrier - it is very moisture permeable. We ran our vapor barrier all the way up the walls and folded, stapled, and caulked all seams.
We still haven't got the foundation people to come look at things (we've had several recommendations for Payeur Foundations) and they seem very nice on the phone, but all estimates are done by the owner and he seems busy. Haven't even scheduled a time yet. A radon man looked at things. After various discussion, he concluded that we needed a true vapor barrier in the crawlspace. There are evidentally very rare, as builders like poking holes in them. Partly just for various pipes and things to go through, but partly because it makes the concrete set faster, and sitting around waiting for the concrete to set is boring. Anyway, he seemed to think that if we replace the existing ceramic pipe with a pourous plastic pipe, level out the floor (eg, with gravel), and put down a good vapor barrier, then we can handle the radon by attaching a pump to the cleanout for the drain. This creates a negative pressure under the floor and keeps radon from seeping in. As long as the vapor barrier is there, it doesn't matter much if there is concrete or not.
The concrete would be only to protect the vapor barrier in case you wanted to walk on it or store things on it. If you are blowing air out, where is the replacement air going to come from? Outside or inside the house? If it comes from inside, the house will be a bit draftier.
I put a vapor barrier under our basement floor at the new house we built. The concrete crew did NOT puncture it as I covered it with 2 to 3" or sand and watched while they worked. I also installed perforated drain tile under the floor and ran it to a standard sump. Sealing the vapor barrier to the walls was a very difficult task. I was also unsuccessful at it. Radon in the basement was over 50 pico-curi. Anything over 4 is considered bad. A $5 centrifugal fan inside the sealed sump, blowing through 1 1/2" PVC to the outside, brought radon levels down to 2. Jan, I also have some *really good* vapor barrier left over from my house that you are welcome to use. I'm pretty sure I have plenty to do your crawl-space.
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