Keeping Things Low and Dry
September 18, 2011 3:05 PM   Subscribe

Once we get rid of all the mold, what's the best way to moisture-proof our crawlspace?

So we escaped hurricane Irene and made it to Disney World just fine! Hurrah! But that meant we weren't home during Irene, and didn't know whether the crawlspace under our house flooded or not. And there was a decidedly musty aroma in the house when we got back from vacation... suspicious.

Soooo we went to take a look at the crawlspace under our house, and found that the insulation under the floor was visibly water-damaged, with the vapor barrier hanging down in places. We don't know if it was from the hurricane or not, but we suspect it's actually been falling apart for some time and we never thought to look before. So I used ServiceMagic to get quotes from three mold remediation dudes.

Mold Remediation Guy #1 wants to remove the old insulation, put down a mold bio-cide, apply a foundation sealant and anti-microbial encapsulation, and then put in R-19 insulation.

Mold Remediation guy #2 wants to remove the old insulation, sand the joists and subfloor, fog the area with a mold-killing chemical, put in R-30 insulation, and install a dehumidifier.

Mold Remediation Guy #3 has not yet given us a quote, but he did find a hive of bumble bees down there, which we had removed yesterday. >_<

Both #1 and #2 said the old insulation was done wrong -- #1 says it was the wrong kind, and #2 said it was put in backwards with the foil facing up and not down. They seem to agree the vapor barrier shouldn't have been between the insulation and the air of the crawlspace, but should instead have been between the subfloor and the insulation. Sigh. Before we had it put in about eight years ago, there was no insulation under there at all.

More information that might be helpful: The crawlspace is external access, about three feet high, apparently home to millions of giant crickets. It has no windows and is not ventilated. This is on Long Island, New York, so quite humid and a lot of variance in temperature.

To get into the crawlspace, you go down a few cement steps to a little wooden door in the side of the house. There is a drain at the bottom of the steps, but I'm not sure if it's working, and I suspect that if the steps aren't covered, water would enter the crawlspace when it rains. The steps have until the last week or so been covered by a ramshackle contraption built by the previous owner consisting of plywood covered by astroturf, but this is now rotting to pieces.

tl;dr: I have no idea how to pick between the foundation seal and the dehumidifier. Which is better to keep moisture out of the crawlspace under my house? Or is there some other thing I should be doing and they're both wrong?

Bonus questions: Should we replace the crawlspace door with something more air or water-tight? Do people traditionally cover the steps down to an external crawlspace, and if so, with what? How do we find out if that drain is still functional, and what do we do if it isn't? In general, is there anything I need to know about keeping this awful space under the house dry?!
posted by Andrhia to Home & Garden (2 answers total) 1 user marked this as a favorite
Let's cover these individual items separately.
* Mold. Was there actual mold? Did any of your contractors test for it? Or did you just go with grimy/nasty under-house look? This may be worth doing before spending thousands of dollars. Remember, when you call a guy to your house and ask "Is there anything you think we should do?" he's probably going to give you a list instead of telling you you're fine. (A home inspector, engineer, or other consultant who is NOT bidding on the job can give you a more honest answer.)
* Removing old insulation. This is pretty basic when you have water damage and mold; but on the other hand, fiberglass doesn't rot. But as to the existing vapor barrier, if there is one, it should be on the top (against the subfloor), not the bottom. The subfloor will normally be warmer than the crawlspace, so the vapor barrier protects the subfloor from the condensation. If the vapor barrier was on the outside, this could have led to mold growth within the insulation and joist area, irrespective of whether you have an actual dampness problem.
* Mold bio-cide or fogger. These seem the same thing more or less. What works best, though, may depend on materials and mold types, so I don't know that there's an inherent best choice.
* Sanding wood surfaces. This might be overkill. What you need to do is kill the mold; after that, encapsulating it (e.g. with a paint like Kilz if you're talking about drywall) can be all you need to do. Some people (insurance companies, maybe?) like the mold to be utterly gone, baby, gone.
* Foundation sealant. This would be good -- if there's significant water entry via the foundation. It could also be not so good. Will the sealant be on the outside? How deep will it go? Will visually covering your foundation from the outside open you up to invisible termite damage (check your local risk)? But if there isn't much water getting in that way it might not really help. If crickets are getting in (the door?) you need to fix that, rather than seal your foundation.
* Dehumidifier. This is only useful, again, if you have an ongoing dampness issue. In general, it's cheaper and more effective in the long run to find out why and how the water is getting in, and stop it from doing that, than it is to remove it using essentially a small air conditioner.
* Vapor barrier on the crawlspace floor. Oh, nobody mentioned this. Why not? It's pretty basic in modern crawlspace management.

As to the entryway, yes, make sure that drain drains; you can use your garden hose to test it, and Roto-Rooter or a plumber to clear it if blocked. The cap you would put on such an entryway is usually more for weather purposes than watertightness. If you have a regular problem with water overflowing into the entry, you have to fix the water drainage on your property (french drains, dry well or rain garden, swales, etc.). The door should be weathertight but not watertight. As a cover you should get what is termed a cellar door or basement walk-out cover (once wood, they are now usually steel). Ventilation may be something to consider, or not; some houses have crawlspace vents you're supposed to open and shut with the seasons, others don't. It depends a little bit on your situation. In fact, you can get vent fans that might obviate the need for dehumidification.
posted by dhartung at 5:48 PM on September 18, 2011

Response by poster: We haven't done actual testing for mold; you can see the stuff pretty easily. There are areas that look OK, but I wouldn't trust that it isn't molding up against the subfloor.

The vapor barrier was very definitely on the outside -- which is to say, when you went down there, you saw plastic sheeting above you, and not fiberglass cotton candy.

Also, guy #3 has come in with his estimate; he's only willing to do the removal and treating, and is punting any re-insulating or moisture control to someone else. All three estimates for remove-and-treat seem to come in at about the same cost, the differences are all in re-insulating and future prevention.

You make excellent points regarding figuring out why the crawlspace is damp in the first place... and how those crickets are getting in. And that hive of bees. We'll probably have to investigate this after the place is cleaned out of the old insulation, though, to be able to get a good look. :/ And it's a good bet we need to replace that door at any rate -- it's got an inch-high gap under it. I'm having a lot of trouble finding a suitable candidate, though.
posted by Andrhia at 6:52 AM on September 19, 2011

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