In part 3 of a five-part series on building a Passive House, architect Steve Baczek explains how he and his crew designed and built a concrete slab insulated to R-50. He chose to use 10 in. of EPS under the slab: a 4-in. layer atop a 6-in. layer. Using foam this thick meant that Baczek had to develop some new techniques: using a reciprocating saw rather than a tablesaw or circular saw to cut the foam; drilling a pilot hole for a penetration, then drilling from both sides of the foam with a spade bit; and tacking the inside pieces of foam to the first layer of foam to keep them from shifting. After the slab was poured, workers bumped up the R-value of the floor by fastening pressure-treated 2×4 sleepers to the slab, then fitting pieces of rigid foam between the sleepers and filling remaining gaps with spray foam. Only then did they install the subfloor.
[To read more of Steve Baczek’s article from the April/May 2014 issue of Fine Homebuilding, click the link below.]