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:
- Some brands of foam have been approved for use as a WRB, while others have not.
- Even if you choose a code-approved foam, you can run afoul of your local building inspector if you don’t follow strict fastening and seam-sealing details.
- According to some building experts, even excellent installations (using an approved foam and approved seam-sealing details) may not be durable.
The code calls for asphalt felt
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.
Other approved water-resistive barriers
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…