- Q.Since ventilated attics can
be breezy, doesn’t the wind rob heat from the
insulated ceiling? Would it help to install housewrap
on top of the R-38 fiberglass batt insulation? If the
client wanted a storage area, I could install plywood
over the housewrap. Similarly, would it help to have
housewrap on the back of second-floor kneewalls, which
I typically insulate with R-24 batts?
A. Don Fugler, senior researcher at
Canada Mortgage and Housing Corp., responds:
Let’s answer the easy question first. In
my opinion, you could put housewrap on the back
side of the second-floor kneewalls in a
well-ventilated attic. This would reduce wind
washing of the insulation. The installation is
roughly in keeping with the standard practice of
using housewrap on exterior surfaces.
As for the attic floor, I would not put a
housewrap and plywood over the insulation. DuPont,
the manufacturer of Tyvek, advises that their
Homewrap is not recommended for horizontal
applications.
I prefer board sheathing to plywood for the
attic floor. Plywood has a relatively low moisture
permeance, similar to that of painted drywall, so
there could be moisture problems on the underside
of the plywood. Boards would be more moisture
permeable, would provide adequate wind protection,
and would make a suitable floor for storage.