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.

 
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