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I take pride in the energy efficiency of my company's homes. Besides building thick, well-insulated walls, I also practice good vapor and air sealing, which includes carefully insulating and sealing the perimeter of the floor joist system. This is easy to do with a conventionally framed floor system. We just install 6-inchthick, R-19 fiberglass batts behind the band joist and hold them in place with tightly fitting pieces of 1/2-inchthick foil-faced rigid foam sheathing. The foam has an insulating value of R-7.5 per inch and serves as both an air barrier and a vapor retarder. About two years ago, however, we stopped framing floors with 2x12s and instead switched to parallel-chord floor trusses. We've found trusses to be more cost-effective,