Here’s the deal. I’m in a serious winter climate, with temps down to 40 below sometimes. We’ll build a two-story house with most all the main floor being on a slab. The perimeter will have footings below frost line, with 8″ frostwalls coming up to the slab. I’ll insulate under the slab with 2″ Dow foamboard, but the Dow folks say that coming inboard beyond 4 feet from the frostwall is a waste of foam and money. The question is regarding two things, the frostwall insulation and the joint at slab and frostwall. Do I insulate the outside of the frostwall, or the inside? Should my slab edge go into a continuous rebate (notch) at the top inside of the walls? Should the slab edge be isolated from the wall by a thin strip, say 1/2″, of foamboard? What are the recommendations?
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Replies
isolate the whole slab to R-10 or better.. the whole slab...
the guys at dow saying it's a waste of time & money should find another job...
what is the constant temp. where you live at 24" down... ? is it 40 ? is it 45 ?
either way, the delta -T is either 30 deg.. or 25 deg... 24 hours a day for the entire heating season... so you build a super insulated house and here's this giant heat loss right under your feet... hmmm
Mike Smith Rhode Island : Design / Build / Repair / Restore
Treading gently in territory not my own, but insulating outside a basement wall will aid in preventing moisture buildup inside, or so I've been told. Around here this is done after the waterproofer is sprayed on the bsmt walls. I think it is 2" pinkboard, they just stick it to the outside and the backfill holds it. We insulate inside as well, and I've got a space heater running next to me, so bsmts still get cooler than the rest of the house. It's probably 40 above here at the moment.
Gene, a rep I talked to at R-control told me to do the entire slab. All literature says 4' is sufficient. All the building texts I have say 4', Joe Listbrek's/Taunton Press "Building in Cold Climate" says 4'.
Details show insulation down on the inside & under slab to the perimeter with a break with foam. I think that book shows a dozen different details with various combinations of walls and footing, some with foam on the outside also. Worth buying, there's a lot of good info in it and fairly current too. Joe H