Existing non-vented crawl space conversion and mold
Hi Everyone,
We’re currently having mold remediation quoted for the non-vented crawl space in our house built in the late 1950’s. It’s in the metro NYC area. The previous owner (we just purchased the house knowing about the problems), had a shower that was leaking into the crawlspace and it has since rotted out the sub-floor under the shower and mold has grown on the sheetrock adjacent to the shower. All of the mold remediation companies we spoke with said this is easy to remediate and not a bad situation. To add to the moisture and mold causing problems in the crawl space, the previous owner had installed fiberglass insulation between the floor joists and also had vinyl flooring on the floor above. Thankfully the crawl space already has a rat slab although without an additional vapor barrier or insulation below considering it was put in when the house and additions were built. The walls are CMU with a painted parging on the exterior. The crawl space is open to the attached garage. The site has decent drainage and a fair amount of ledge around the house and under the slab.
One company we spoke with for the remediation also completes crawl space conversions from non-vented to vented and they are suggesting some things I’ve never read before on the forums and I’m curious what everyone thinks. Their proposal on the conversion is as follows:
1. Seal exterior vents with plates (didn’t specify type and I haven’t asked yet)
2. Air seal penetrations including plumbing stacks, electrical cables, duct penetrations
3. Install 3-1/2″ Roxul Insulation (R-15) at rim joists and spray foam seal into place
4. They said they could install Roxul against the foundation wall as well if we wanted
Originally I was thinking I would place rigid insulation at the rim joist and spray foam into place. I hadn’t yet decided what to do on the walls which brought me back to reading the forums here. I asked why the company doesn’t use rigid insulation and I was told it isn’t fire rated and it’s not moisture resistant. I mentioned foil faced polyiso being fire resistant and I was told that I can’t trust techniques that I read on google and that they’ve been doing conversions this way for at least three years without any issues. I asked how they did it before and they told me they used batt – I quickly replied that clearly that didn’t work out in the long term and they had nothing to say. I’m worried to go down the wrong path and here I am trusting the experts here rather than what I read on google or heard from this company.
Something to add is that we plan to in the next few years re-side the exterior of the house and hopefully will install a rainscreen with rigid foam on the exterior of the house. I’m not sure if that changes things (but I am thinking we could do some work on the exterior of the foundation at that time if it’s warranted). Ultimately I don’t fully understand why crawl spaces are treated differently than basements since they’re just shorter versions of them but that has been debated enough on these forums.
Follow up questions:
1. Should we use Roxul or no?
2. Should we insulate the walls? With Roxul or no?
3. Should we close up the vents with exterior applied metal or plastic panels or use CMU and parge to match the adjacent? If it doesn’t matter we’ll wait on the CMU and parging for a few years until we redo the siding.
4. Should we have them install a dehumidifier in the crawl space or wait to see what the humidity levels are after they convert it?
5. Should we ultimately condition the air in the crawl space since the air can transfer through the floors anyhow? We could also open a vent to the house to allow air transfer and not directly condition the space.
6. Should we close up the connection to the garage with an insulated removal panel or leave it open?
7. Is there anything else we should be doing to help encapsulate the crawl space?
8. We passed a Radon test but now we would be closing in the crawl space – is this something we need to retest once the crawl space is enclosed or should we be fine?
Thank you very much in advance for your help on this. I always enjoy reading the forums whether they apply to my situation or not!
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Replies
S.G.,
We need to know your climate zone. Using Roxul at a rim joist is especially risky in cold climates -- less risky in warmer climates.
[P.S. -- Sorry that I missed the reference to "metro New York."]
Sorry I didn't specify and only said metro NYC. I'm technically in Climate Zone 4 but border Zone 5. We're in Westchester county, NY.
S.G.,
If this were my house, I would certainly go with rigid foam -- for example, Thermax -- rather than an air-permeable insulation like Roxul.
Metro NYC is zone 4A.
In that climate you can probably get away with Roxul on the band joists, but it's better if you air-seal and insulate the band joist & foundation sill with a flash-inch of closed cell spray polyurethane, which would form a non-wicking semi-permeable condensing surface, without unduly restricting the drying capacity toward the interior.
In the description of work I don't see air-sealing the band joist & foundation sill, air-sealing the CMU (it leaks- trust me), or the installation of a vapor barrier over the rat slab and sub-grade portion of the foundation walls, all of which are critical details.
IRC code min insulation for foundation walls for zone 4A is R10 continuous insulation, or R13 if it's an insulated studwall. If you installed the ground vapor barrier lapping it up 12" up the foundation wall and installed 2" foil faced fire-rated polyiso (Dow Thermax) sealed to the vapor barrier and affixed in place with 1x furring through-screwed to the CMU with 4" TapCons you'd be there. You'd have to cut'n'cobble rigid foam over any ledge at the top of the foundation over to the foundation sill or cover it with your flash-foam on the band-joist before installing the R15 fiber.
Code min for zone 5 is R15 continuous insulation or R19 in studs. R15 would take 3" polyiso and much longer TapCons. Sometimes it's easier to just trap 1-1.5" of foil faced polyiso to the foundation wall with a non-structural 2x4 studwall and put batts in the studwall to achieve the same performance.
Be sure to tape any of the seams between foil-faced foam with a high quality foil tape.
"Install 3-1/2" Roxul Insulation (R-15) at rim joists and spray foam seal into place."
The idea of sealing the Roxul boards in place with spray foam makes it sound like they think they are going to provide air and/or vapor sealing. Roxul boards are highly permeable, so that really doesn't make sense. It sounds like you've found one of the many misinformed contractors in the US.
An alternative would be to insulate the outside of the foundation with Roxul boards. But it seems easier to go with Martin's advice.
Thank you Dana and Martin. Since you didn't address the remaining questions I assume they're not relevant after your suggestions are completed?
Dana,
1. Would the vapor barrier air seal the CMU wall or is there something else you recommend? Does the stucco parging on the exterior not also air seal the CMU?
2. If we end up doing the work ourselves we would need to use Martin's idea of rigid foam at the rim joist rather than the flash-inch of spray foam. Is there anything else you would add to the installation of the rigid foam with spray foam at the edges?
3. How do you recommend sealing the rim joist and sill if we don't use spray foam per question number 2?
4. Is it worth bringing the vapor barrier up to the sill plate in all locations even if it's above grade?
5. You would be comfortable installing R15 fiber at the rim in the crawlspace even though it could absorb the remaining moisture in the crawl space?
Martin, are there cheaper alternatives to the Thermax?
Charlie, the worst part is they are a large outfit here and "specialize" in crawl spaces. In a way it might be easier to insulate the exterior down to the footing but I'd still have to handle the vapor on the interior.
S.G.,
Have you read this article?
Building an Unvented Crawl Space