Sheathing and WRB Choices: Plywood with an applied membrane or ZIP System? – GreenBuildingAdvisor

By Chuck Bickford | February 10, 2025

Some components of a building have simple roles, while others are meant to multi-task. Take sheathing, for instance. In most buildings, the fundamental job of the sheathing is structural. But the way many people build today, it may also be responsible for keeping air and water from penetrating the building enclosure. To perform these functions, sheathing needs certain characteristics—it needs to be structurally rigid, air impermeable (with sealed seams), and water resistant (or covered with a product that is). In many cases, sheathing (and the water-resistant barrier, or WRB it is paired with) is also expected to allow any moisture in the wall to dry to the outside. In other words, whether the sheathing has one job or many, we want it and the WRB that is used with it to have the right permeability. This last task has become an important design characteristic in residential construction, with more building professional becoming savvy to the importance of drying potential.

This brings us to the recent Q&A posted by DaveP66 (we’ll just call him Dave). Dave and his wife are building a small house in South Florida. It’s stick framed on a slab, but he’s been flummoxed by the number of choices when it comes to sheathing and WRBs. He writes that his top priorities are weather-resistance and structural strength, but he’s also concerned about the chosen material’s ability to withstand prolonged exposure. “We’re building this ourselves while working full time, so we may not get it fully dried in as fast as we’d like,” he wrote.

His first choice was to use plywood with Sharkskin Ultra SA underlayment for the roof, and ZIP System sheathing for the walls. But then he started reading about Advantech sheathing and it seems very…