Attic insulation under and over plywood.
You all have convinced me that compressing insulation lowers its
value, and that houses with truss roofs weren't meant to have floors
in the attic. But what about leaving the fiberglass that rises to
the level of bottom rail of the trusses, putting a layer of plywood in
those places where I might have to go in the future, and putting
another 4 or 6 or even 8 inches of insulation above that? Wouldn't
that be the best of both worlds?
Then I won't lose my balance and fall through the ceiling when I crawl
out there, and the fiberglass above the plywood will be compressed
when I kneel on it, but will probably spring back pretty quickly. Or
I can fluff it up when I leave.
I looked up the R-value for plywood and it is pretty low, but that was
plywood used as siding. When plywood is used horizontally, seems to
me it eliminates heat loss through convection, even more effectively
than fiberglass. I would think even 3/8" of plywood is as effective
as 2 or more inches of fiberglass in preventing heat rising through
convection. Except around the edges of course, although since it's
not a real floor, some edges could be eliminated through overlaying.
There are times when I have to go out from the center of the attic to
install wiring, for lights, telphones, smoke or burglar alarms, and
speaker wires, plus more. Right now there is a problem with the phone
line to my bedroom. A cordless phone is not a permanent option.