A water-resistive barrier (WRB) provides protection against water damage for water that gets behind the cladding of a building. But what if it doesn’t really resist water? I’ve written a lot about installation problems that can lead to compromised water resistance. (See the article I wrote last week, for example.) But other factors can make them leaky, too. Too much exposure to ultraviolet (UV) light is one of them.
At the Air Barrier Association of America conference in Baltimore last month, I attended a presentation by Marcus Jablonka of Cosella-Dörken. [Editor’s note: Cosella-Dörken is a manufacturer of water-resistive barriers.] The manufacturer has done a study of UV exposure to different WRBs, and the results should be of great concern to all builders, architects, and product specifiers. This is a preliminary study and there are still a lot of questions to be answered, but I’d be concerned if I were a builder.
A short primer on water-resistive barriers
As mentioned above, the WRB’s purpose is to allow water that gets behind the cladding to drain down and be removed from the building. They come in different flavors and have a variety of properties. First, you can get your WRB as a material that is:
Some properties are more important than others. Building enclosure control freaks understand that you need to control the flows of heat, air, and moisture to have a building that functions well. Controlling heat is typically not done by WRBs (although it can be), so let’s focus on liquid water, air, and water vapor.
No matter which WRB type you choose, you want it to have a high water resistance. Yes, I really said that. As obvious as it seems, sometimes it’s good to state — and question…