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.
One additional choice, if you are choosing to use a layer of continuous exterior insulation, like Rockwool, the insulation itself may also act as the WRB. Check with the manufacturer of the insulation for details.
How we connect the WRB to a window or door will depend on many factors, including the following:
Because all of these factors must be taken into consideration in order to properly integrate a window or door with the WRB, installation methods will vary. However, my high-level advice is to think like a water droplet, which usually flows down with gravity and is directed out and away from the wall with flashing. Ask yourself: Where will water flow when it gets in between the cladding and the WRB? You want to make sure it will find a pathway down the WRB to the ground or cladding and, from there, down to the ground. Keep the water moving and provide avenues for exit, because any water that gets stuck has the potential to damage the structure.
Code requirements for WRBs and windows
When it comes to integrating windows and doors with the water (and air) barrier, the code has specific requirements. Sometimes code language can be a little confusing, so I’ll break down the code as we move through the reference.
Flashing at exterior window and door openings shall be installed in accordance with one or more of the following:
Thus, you should first follow the window or door manufacturer’s installation instructions and then the WRB manufacturer’s instructions. You can find instructions tailored to your product and project through Andersen’s Installation Configurator.
You can order installation materials, including sealants, shims, fasteners, canned expanding foam, backer rods, and more through the Andersen Parts Store.
In R703.4 Flashing installation at exterior window and door openings, the code states:
Flashing at exterior window and door openings shall extend to the surface of the exterior wall finish or the water-resistive barrier
complying with section 703.2 for subsequent drainage.
The code requires the window and WRB to be flashed so any water that finds its way behind the cladding can be either kicked back to the cladding at the window or continue down the WRB. We do not want water to find a pathway into the window rough opening or between the WRB and wall sheathing/framing.
Air sealing shall be installed around all window and door openings on the interior side of the rough opening gap.
Continuity of the air barrier (air sealing) will typically happen at the interior of the window, and there are several different methods that can be used. Watch for a future blog post on air-sealing a window.
Mechanically attached flexible flashings shall comply with AAMA 712.
AAMA stands for American Architectural Manufacturers Association. The association provides performance standards for the installation of windows and doors. AAMA 711 applies to self-adhered membranes, AAMA 712 covers mechanically attached flexible flashings, and AAMA 714 is for fluid-applied membranes.
Tips for integrating WRBs and windows
Here are a couple of things to keep in mind when integrating your chosen WRB with windows:
Randy Williams started his construction career in the mid-1990s installing electrical, plumbing, and HVAC systems with his brother. In the early 2000s, his family branched into building and renovating homes. By 2005, Randy was working full time as a general contractor. He furthered his education in 2009 becoming an energy auditor. Today, Randy works with other contractors, homeowners, and utilities performing energy audits, building diagnostics, energy design, and code compliant testing, and assisting in the design of energy-efficient homes. He is also a contributing author to several trade publications and occasionally teaches home diagnostic testing and building science topics at different trade shows and training events.
In his nearly 30 years in the construction industry, Randy Williams has seen a lot of window installations — both good ones and bad ones. In this article, he’s sharing his top tips for avoiding common mistakes and installing windows successfully.
Ready for a crash course in one of building science’s core concepts? Get to know the four control layers and how they relate to your construction plans and window and door choices in this piece by guest contributor Randy Williams.
