Spray foam in crawlspace (with apologies)
Hey folks,
I used to hang around here a bit, but I drifted away about 8 years ago. Now I’m back looking for help.
I’m sure this has been discussed to death over and over, but my search-fu is weak tonight and I haven’t found anything relevant.
Perhaps somebody can point me to a useful thread or give me a Reader’s Digest answer.
Background: I’m in SW Virginia – a fairly humid climate with a pretty even balance between heating and cooling. My formerly inexplicably dry crawlspace got inexplicably damp and developed mold on the floor joists. (Inexplicable: when I moved in, the yard was soggy and sloped toward the foundation. I regraded it to drain away and the yard isn’t soggy any more. But the crawlspace is damp. There’s more, but too many variables for me to analyze).
The crawlspace is just that – a place to crawl under the house. It ranges from hands & knees to belly-crawl space. It has the typical vents in the typical CMU foundation wall. About 75% of the dirt floor space is covered with poly film. It’s got spiders and snake skins and no evidence of plumbing leaks.
I’m confident that I can greatly reduce the dampness by replacing the existing partial vapor barrier in the crawlspace with total coverage of 6 mil poly and detailing the yard drainage a bit more. I’m fully aware that there are more comprehensive approaches to this issue, such as full encapsulation/insulation and converting the crawlspace to conditioned space, but I have to save money for inconsequentials like food and the mortgage. Like many others, I’m struggling financially. A few years ago, I would have thrown a few thousand extra bucks at it, but I can’t do that now.
As part of the mold remediation, we will be removing all of the saggy fiberglass batt insulation. We will also properly disinfect the mold on the framing. (I work with a qualified mold remediator, and he owes me a favor. We’ll be spending a weekend scrubbing the joists).
My actual question has to do with insulation. According to the quotes to date, I can go back with nominal R19 FG batts for about $.60/sf, or nominal 5″ OC foam for about $1.70/sf, or nominal 2″ CC foam for about $2.125/sf.
I expect to greatly improve but not eliminate the dampness issue.
I think I need to control air infiltration to keep any residual mold out of the house. I know that FG batts won’t do much for that. I’m leaning hard toward spray foam, but I haven’t been able to sift through the marketing BS about OC vs CC foam. It appears that CC is a better moisture barrier, but it’s unclear whether I need a moisture barrier or just an air barrier. I’m not convinced that trying to keep the moisture from moving from the crawl space to the living space is a good idea. I’m assuming that mold spores move with air rather than water.
Oops – I guess I haven’t actually asked a question. What do you recommend?
Having asked that, I’m going to be out of town for a couple of days and won’t be able to reply for a bit. Feel free to dopeslap me and point me toward whatever painfully obvious answer that I’ve missed.
Cheers, Gravy
Replies
If you put the 6mil VB down, it should control the moisture getting into the crawlspace. Controlling the moisture movement up into the living space is not really an issue as you said ... doesn't mean you don't want to control the moisture in the crawl, though. As moisture moves up the air dries out. If you had enough RH to condense on the joists, you have/had an issue and drying out the crawl is very important. Controlling the moisture intrusion is also important.
You talking about foaming the floor or the crawl walls?
I know little about OC vs CC
Installing the VB is a given. The moldy areas are mostly above the gaps in the existing VB.
I'm looking at foaming the underside of the floor in order to keep any residual mold out of the living space. VB to dry out the crawlspace and starve the mold, disinfect the visible mold, and foam to limit mold migration to the living space via air infiltration.
With the mitigation action ... laying down another VB and disinfect ... you shouldn't have other mold issues. Mold won't really 'migrate' into the living space. Vapor/moisture that could support mold growth will not be an issue once it reaches the living space. Mold can grow on the new insulation you place if the right conditions exist. Air infiltration into the living space will not likely support or transport mold.
I agree w/ Dan H ... after the mitigation/barrier placement ... allow the crawl to stabilize/climatize. Your methods to control moisture are good, but you are worrying about mold transport and you shouldn't have to. If you have so much mold in the crawl that it has become airborne ... you've got far more serious problems than air leaks into the space.
I'd say put down the vapor barrier and then wait at least a few months before doing anything about insulation. See if the moisture problem clears up. If it doesn't, find and fix whatever's wrong before insulating.
The old insulation has to go in order to disinfect the mold on the framing. The plan is: remove the contaminated FG batts. Disinfect the framing. Remove the contaminated VB. Seal the vents. Install new insulation.
As of today, I've identified several oopsies that have likely contributed to the dampness - grading and gutter problems that I brought upon myself, as well as gaps in the existing VB. Fixing those problems should dry out the crawlspace sufficiently to prevent new mold growth.
At present, the most believable proposal has been to replace the old FG batts with 5"OC foam. The argument is that the OC foam is a good air barrier, but it won't trap moisture. The cheapest option by far is to install new FG, but I think that we need better control of air infiltration.
I'm still educating myself and I may change my mind. For now, I'm going to get the old FG removed and clean the bulk of the mold off of the framing. That will take me into the beginning of March. I'm hoping that by that time I will have a better idea of what is likely to work within my budget.
I've gotta vent here: This is really frustrating for me. I want to fix this right, but I just can't do it now. If I had tens of thousands of bucks and hundreds of hours to throw at this project, it would be a no-brainer. I'd fully decontaminate and encapsulate the crawlspace and attic, and maybe add HEPA air purifiers, dehumidifiers, and an HRV or two. Unfortunately, that would require resources that I don't have at present. As it is, I have to figure out workable compromises that will let me pay the mortgage, buy food, and let my wife breathe in the house.
OK. Enough whining. Suggestions are welcomed.
Over at Building Science they are recommending attaching 2" rigid foam board to the bottom of the floor joists and sealing the seams. This will insulate and keep out vapor, plus it's easy to do and likely cheaper than the other options.
I'm not sure about making the crawlspace part of the conditioned space in the house. First, why would you then insulate the underside of the floor joists? I'm thinking in terms of a basement (which are common here in Iowa), which is part of the conditioned space. One typically insulates the basement floor slab, and the basement walls (including rim joist, very important), but not the underside of the first floor joists.
I'm thinking the better approach to control humidity in the crawlspace is to keep it sealed off from the main living space, but increase your ventilation and decrease your moisture infiltration from the soil. Some kind of forced air system which pulls in fresh air on one side of the crawlspace and exhausts it on the other side would be a good thing, I'd think. With enough airflow, and a good continuous vapor barrier on the floor of the crawlspace, I'd think you'd have licked most of your problem. Complete coverage of all of the soil, with all seams taped. You could run the plastic up the foundation walls a couple inches too, and paste the plastic to the concrete with a bit of caulk, for even better blockage.
As for insulating the joists, another option you might consider (in lieu of 5" foam) is to put up a thinner layer of foam, backed with unfaced fiberglass. You generally want your vapor barrier on the warm side of the wall (or floor, in this case), but in a mixed heating/cooling environment as you describe, I think it would be a good thing to have a chunk of foam serve as the vapor barrier itself. So long as the cold side of the vapor barrier (i.e. the foam sheet) doesn't drop below the dew point, you shouldn't get condensation on its surface. I believe a recent FHB article was talking about the cost benefit of using a thinner layer of foam combined with traditional insulation (fiberglass or cellulose), instead of having the full thickness coming from foam. If the foam is thick enough, it won't allow condensation to form on either surface, because the warm and moist side will always stay above the dew point. In the summer, the underside of the foam will stay warm, and in the winter the top side of the foam (resting right under the subfloor) would stay warm too. I would guess that 2" of rigid foam would be enough. I'd cut it to fit in your joist spaces, and just use spray foam to seal the edges and joints. Then you can fill in with cheaper fiberglass.
All of these replies have got me rethinking my strategy. We're going to have the old contaminated FG batts removed and we're going to disinfect the moldy joists. Then we're going to make sure that runoff drains away from the building. Then we're going to spend some of the warm season trying to figure out whether we're better off insulating the floor or the crawlspace perimeter, and how to detail the VB.
Somebody please warn me if I'm being an idjit...
Oh. So that's what that exudation is called. To the unitiated, it smells a lot like...uhhh, nevermind (grin).
Seriously, thanks for the advice. I'm in the really steep part of the learning curve. I'm transitioning from emergency response to long-term strategy. I'll be back with more questions.
Gravy