Green Insulation Product for Crawlspace
I’m looking for options to take our vented crawlspace (1955 ranch) and turn it into a conditioned space (unvented). The crawl space is 3 blocks tall with a dirt floor. Overall it’s pretty dry with a sand bottom. The house is a mid-century style with a hipped roof and ~18″ overhangs. The house has baseboard radiant heat and was within ~5F of the main floor through most of the winter. That is with the vents closed, but no insulation, just relying on the copper pipes to heat the space. No mechanicals currently in the space, but we will be adding an ERV (with ducts) and possibly a dehumidifier.
承包商我联系了佤邦的低矮的空间nt to use closed-cell foam from the rim joists down to the floor. For code they need to paint a flame retardent — I believe a 30-minute rating.
For our remodel I’ve been trying to avoid spray foam and have been successful so far. Spraying 3-4 ft of foam around the entire perimeter of the house is not something I want to do. It is also very expensive — quotes were $15,000 and $20,000 for full encapsulation.
However, looking into it more it seems like there are very few options that would work that wouldn’t need some kind of flame retardant painted on.
Our contractor recommends 2.5″ of Ox ISO Red Max which is Class A fire rated. However, that seems to be commercial-level stuff that I’m sure is pretty nasty too (contains n-Propyl Bromide?).
I’m considering just doing the rim joists like I’ve done our current house, which is cut-and-cobble XPS with Rockwool in front of it. Then install a 15 mil vapor barrier down on the floor. This would leave the walls un-insulated.
Is there any reasonable “green” option out there to insulate our crawlspace walls, or am I overthinking it? I’m mainly concerned about indoor air quality as I plan on keeping the crawl space access open or at least vented. Also, in the case of a fire, I don’t want to kill the whole neighborhood.
Any suggestions would be greatly appreciated!
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Replies
You'll need a vapor barrier over the dirt floor, code is 6 mil minimum but I'd use at least 10 mil myself. You want to bring that up the walls too.
For insulation, you can use rigid foam in the rim joist area covered with mineral wool since the mienral wool acts as the fire protection. You can save a little money here using the slightly thinner "safe'n'sound" variant too. Note that I prefer to use 2" or thicker EPS here instead of XPS to allow for a small amount of drying. Regardless of the foam you use, BE SURE to seal it in place well with canned foam. I like the Loctite Tite Foam for this, since it's a bit more durable compared to the more common Great Stuf -- and it costs more too.
For the main walls, you really have two options: "regular" foam board with the fire retardant (unless your local code has an exception for inaccessible areas, and your crawlspace MIGHT work here -- call your local building department), or something rated to be left exposed. Dow Thermax and Johns Manville CI Max are both rated to be left exposed, just be sure to install it with the correct side facing inwards.
Another option would be rigid mineral wool panels, whcih are expensive but might be competitive compared with the special polyiso that is rated to be left exposed. Note that there have been reports that some mineral wool products have been difficult to get lately.
BTW, try not to worry too much about what is listed as the component chemicals of rigid foam materials. The final product, be it EPS, XPS, or polyiso, is a very stable material that isn't going to cause you any problems.
Bill
Thank you for the reply. I found a place locally that has Rmax ECOMAXci FR which seems to rely mainly on its 12mil facing as the source of fire resistance. Any experience (or opinion) with this product?
https://www.rmax.com/ecomaxci-fr
https://static1.squarespace.com/static/57a39be0579fb3a3a8540f56/t/5e966629a3a65e6b72b4ca0e/1586914859792/Crawl+Space+Application+Utilizing+Rmax+ECOMAXci+FR.pdf
Both of the two types of polyiso I referenced before also use an extra beefy foil facer on one side to provide the fire resistance, so the product you found isn't really any different in that regard. You've basically found the same thing from a different manufacturer :-)
Bill