Do foam-sheathed walls also need housewrap? There’s no simple answer to the question.
It is possible to use foam sheathing as a water-resistive barrier (WRB). However, those who choose this route should know:
By now, most builders know that wall sheathing needs to be protected with a WRB — for example, asphalt felt or housewrap. (For basic information on WRBs, see All About Water-Resistive Barriers.)
According to the International Residential Code, builders must install a layer of number 15 asphalt felt or paperbacked stucco lath over the wall sheathing or studs of every new home. The code requirement (section R703.2) includes a qualification: if you don’t want to use number 15 asphalt felt, you can use some “other approved water-resistive barrier” (WRB).
The code requirement calling for walls to be covered with number 15 asphalt felt is very odd, because every manufacturer of asphalt felt declares unequivocally that the product is intended for roofs, not walls. In spite of this curious anomaly, asphalt felt performs well when used over wall sheathing as a WRB.
So, what does the code mean by “other approved water-resistive barriers”? Almost anything, as it turns out — as long as the product (or system) has been accepted by the International Code Council Evaluation Service (ICC-ES). If a manufacturer can present adequate evidence to the ICC-ES that a material or system meets “acceptance criteria” established by the ICC-ES for approval, then the ICC-ES will issue an evaluation report approving the product.
Among the products that have been approved as substitutes for number 15 asphalt felt:
If a building inspector challenges your use of Tyvek — “Where’s the asphalt felt?” — all you have to do is show your inspector the relevant evaluation report from the ICC-ES.
The use of rigid foam as a WRB is a relatively new phenomenon. When rigid…