Insulation — basement rim joist
davemax21
| Posted in Green Products and Materials on
Hello
I want to insulate the rim joists of an old home. I have caulked the joists due to openings in the wood from age. I don’t want to use rigid board/spray foam. I was going to use batt insulation (unfinished basement), but wonder if there is something that is not toxic or contains fiberglass, etc.. something i can cut and shove in the openings and just leave it there. I don’t plan on using any plastic, vapor barriers, etc..
Thanks.
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Replies
Dave,
In this location, you can't use an air-permeable insulation like fiberglass, or the rim joist will be at risk for moisture accumulation and rot. You need to choose between rigid foam insulation and spray foam insulation.
For more information, see Insulating Rim Joists.
thank you.what if i did use plastic in the joist first? could i then put batt there?
Dave,
I don't recommend that approach.
Got it. I won't attempt then... batts are just so much easier, trying to get up the energy to handle the rigid, with the cuts, and foam, etc... but thank you.
If you put plastic between the fiber insulation and band joist you risk condensation at mold-inducing levels at the cold side of the batt.
The risk of different approaches varies by climate- where are you?
central ny, syracuse, yes, very very cold .
Naw, Syracuse is US climate zone 5- that's only "kinda cold". It's nothing like the Canadian midwest or northern Minnesota/North Dakota. The binned hourly mean temp for the month of January in Syracuse is about +24F- in Fargo ND it's about +8F, to Winnepeg's +3F, a mere 100 miles north of the border. In cooler places like Churchill Manitoba ( on Hudson Bay) the mean January temp is -15F- that would be "very very cold" in my book. ;-)
But Syracuse weather is cold enough to be an issue.
If you install a thin plywood air-barrier at the desired depth and dense-pack behind it with cellulose you'll be OK just painting the plywood with "vapor barrier" latex, which runs about 0.5 perms. But making the plywood reliably air-tight could be tough without using some amount of spray foam, or at the very least acoustic sealant caulk.
A minimal foam, minimal outgassing alternative would be to put cut'n'cobbled 2" (R8) EPS up against the band joist (sealed in place with can-foam) and R15 rock wool batts snug up against the EPS on the interior side, with cut'n'cobbled wallboard painted with a standard latex primer (not vapor barrier) as the interior side air barrier.
EPS is blown with pentane, which outgasses quickly- 99.9% gone by the time it hits the distributor's loading dock. The binders used in making rock wool batts get cooked out from the high processing temperatures during manufacture. (The fibers are denser & stronger than fiberglass, and particles from cutting don't hang in the air as long either.) Can-foams typically use propane /isobutane propellants as the blowing agent, which outgasses fully within a few weeks. ( A typical MSDS sheet: http://www.dow.com/webapps/msds/ShowPDF.aspx?id=090003e8800c2cd4 ) The greatest exposure risk is while you are actively installing it. If that is objectionable I suppose you could use acoustic sealant caulk for sealing the foam to the wood, which uses heavier less volatile hydrocarbons: http://www.tremcosealants.com/fileshare/msds/93170X_330_C.pdf