Window installation and water resistive barriers (WRBs)

I’ve heard building scientists claim that rainfall that contacts the cladding can, during wind-driven rainstorms, end up between the cladding and WRB. This same moisture has the potential to make its way around a window, door, or other planned penetration. Properly installing a window or door involves proper integration with the WRB, so let’s explore what you need to know.

Need to back up a step? Gain an understanding of the importance of the water control layer and an introduction to the four control layers in my piece, Understanding control layers.

A WRB is a material or finish that helps reduce water intrusion. It’s intended to help keep a building element or assembly dry. It’s a term that’s often used interchangeably with housewrap, which is a specific type of WRB, but not the only type. Residential building codes require the use of a WRB. The code language is found in the 2021 IRC, R703.2 Water-resistive barrier.

Not fewer than one layer of water-resistive barrier shall be applied over studs or sheathing of all exterior walls with
flashing as indicated in Section R703.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer … 

But of course, the WRB is not just a code requirement, it’s an element that’s integral to the integrity of the building. And since windows and doors are too, it’s important to understand how to properly integrate them with your chosen WRB.

Let’s explore the four main types of WRBs currently on the market. 

1. Mechanically attached products, usually called housewraps, are synthetic sheets that are typically fastened to the structure using a cap fastener or cap nail. Example brands include Tyvek and Typar. In addition, there’s an upgraded option within this category that includes a drainage plane that’s integrated into the wrap. Drainable housewraps are typically installed like a traditional housewrap. Benjamin Obdyke and DuPont both make these types of products.
2. Fully or factory-adhered products are sheathing panels that have a factory-applied barrier. The sheathing is nailed to the wall framing, and all seams and penetrations are sealed using tapes and/or sealants. Examples include Huber’s Zip System and LP’s Weather Logic products.
3. Self-adhered products are basically giant pieces of tape that are stuck to the wall sheathing. All seams are lapped by the adjacent self-adhered WRB and, much like the fully or factory-adhered options, penetrations are sealed using tapes or sealants. Henry Blueskin and Siga’s Majvest SA are two options.
4. Fluid- or liquid-applied products are rolled on or sprayed to the wall sheathing, usually before any penetrations, such as windows and doors, are installed. Tapes or sealants are used to connect the planned opening and penetrations to the WRB. PROSOCO Cat 5 and Henry Air-Bloc All Weather STPE are a couple examples. Be sure to check the permeance, or perm rating, of fluid- or liquid-applied WRBs, as some are formulated for specific climates.