- Q.Can I use rigid foam panels
sandwiched between subfloor and finish floor to
insulate over a crawlspace?
A. This can be done, but I
would not recommend it. Movement of anything
against polystyrene foam creates a terrible
squeaking noise. Remember the last time a foam
cooler rubbed against something in the back of your
Except in the most extreme northern climates,
insulating a floor over a crawlspace is
questionable because you lose some of the cooling
advantage. In the summer, there is considerable
cooling by heat radiating from the floor to the
The best way to insulate a crawlspace is to use
foam on the stem walls. However, if you opt to
insulate the floor cavity, all piping and ductwork
must be insulated also. An inexpensive alternative,
if there are no ducts or pipes in the crawlspace,
is to use a sheet of double-faced reflective
insulation on the bottoms of the floor joists.
Reflective insulation works well against downward
heat flow, yielding up to R-11 if the air space
above is tightly sealed.