Borate Treated XPS needed if installing outside stemwall & partially below grade?
I have a conditioned crawlspace (new construction) so I’m looking at what insulation product to put outside my stemwalls. I’m planning on asphalt damp-proofing under the foamboard (on the stemwall) and a drainage surface (dimpleboard) over the foamboard on the uphill side before backfill. Where the foamboard isn’t backfilled against, I’ll have to cover it with something. My drafting professional suggested a “cementitious board”.
I’m supposed to have R15, so my default choice is probably 3 inches of the pink foam board. However there’s the foil backed rigid insulation also (polyisocyanurate) which apparently is more expensive.
Climate: I’m on the wet side of Oregon, on a nicely sloped hillside. Apparently termites aren’t too bad here.
1. I recall hearing that insects or mice or something likes to eat the pink board. Should I look for a borate treated product? or will covering the insulation with flashing/cementitious board be adequate?
2. I see that the foam backed insulation has a higher r value and higher cost. Is there a difference in how attractive these two are for insects or mice?
(The foil backed insulation is not recommended for below grade.)
3. What ideas are there for covering the foam board insulation on the downhill side of the house where there isn’t much backfill to cover the stemwall (just the minimum 12 inches above footing). Would the normal thing be this cemetitious board (??) with stucco? or just a parge coat applied directly onto the insulation?
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