Q: What type of weather resistive barrier (WRB) should be used behind brick veneer?

A: Matt Risinger, owner of Risinger Homes, a custom builder and whole-house remodeling contractor in Austin, Texas, responds: When selecting the proper WRB for behind a brick veneer, it’s important to understand that brick is not waterproof. In fact, brick is highly porous and absorbs water readily, so it cannot and should not be depended on to stop moisture from entering a wall system.

You also need to realize that brick gives up its moisture pretty readily. That means that it dries quickly to the outside under most conditions. The one exception is when the sun beats down on moisture-laden brick. In that case, solar-driven moisture from the brick is pushed into the air space behind the brick, and unless the proper WRB is in place, the wall sheathing on the other side of the air barrier can be at risk.

I recommend using a WRB with a perm rating lower than that of conventional housewrap. A lower rating means that the WRB is less likely to let moisture from the air space behind the brick reach the wall sheathing. A product like Tyvek CommercialWrap has a perm rating of 23 to 28—compared with a perm rating of 58 for regular Tyvek HomeWrap—and is a better choice for a WRB behind brick veneer. When I’m applying a WRB to sheathing before installing brick veneer, I like to put on a layer of CommercialWrap and cover that with a layer of 15-pound felt as added protection.

I do most of my work in the hot, humid south. In my area, a peel-and-stick membrane, which typically has a perm rating of less than one, can be used as a WRB behind brick veneer. An important caveat for this application is that you must be sure there is no additional vapor barrier inside the walls of the house that could trap moisture and cause damage inside the walls.

Drainage detailing with brick veneer is just as important as the type of WRB material that you choose. All penetrations such as windows and doors should have through-wall flashing that’s integrated into the drainage plane at the sheathing. Through-wall flashing should also be used at the base of the wall, along with weep holes to let any accumulated moisture drain away safely. And finally, I always install mortar net at the bottom of the air space. This mesh product is designed to catch and trap mortar that falls while the brick veneer is being constructed, to keep the weep holes free of debris.