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,