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.