Tar paper as housewrap
stryped1
| Posted in General Questions on
Do you see anything wrong with using tar paper as a housewrap when remodeling?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Don,
Yes, it's perfectly possible to use #15 or #30 asphalt felt as a water-resistive barrier (WRB), as long as it is properly installed and lapped.
For more information, see All About Water-Resistive Barriers.
#30 felt is on the low-permeance end, and may limit the drying capacity of the sheathing. It's customary (and better) to go with #15 felt on wall assemblies, since it has higher (and variable) permeance that won't impede drying nearly as much, but is still a sufficient WRB. (#30 felt is better for roof shingle underlayment though.)
It depends ... and to quote Martin who is quoting JLC:
"Asphalt felt has a permeance of only 5 perms when dry, but a much higher rating of 60 perms when wet. Fans of felt note one of its advantages over housewrap: If water gets behind felt — either due to a flashing leak or condensation from solar-driven moisture — the felt can soak up the liquid water and gradually dry to the exterior."
Tar paper is a less effective air barrier because you don't seal its seams with tape.
Nick,
While that may be true, no one should be depending on housewrap to be an air barrier. The purpose of the asphalt felt (or the housewrap) is to be a barrier to rain that gets past the siding.