Windows Before WRB? – GreenBuildingAdvisor – GWC Mag

There are lots of ways to install weather-tight windows. You might choose to install a sloped rough sill, a back dam, or both. Your sill pan could be site-made or manufactured from plastic or metal. You can protect the inside perimeter of the rough opening with house-wrap or a self-adhering membrane. For flashing, you
can choose between tapes and liquid-applied membranes. You even have options for fasteners—there are nails and screws that can do the job. If you’re following good window-flashing principles today, the window manufacturer’s instructions likely inform the process, and you probably improve on them for added reliability.

For many window installers in North America, though, one major step in the window installation and flashing process probably isn’t a decision consciously made: whether the mechanically fastened water-resistive barrier (WRB)—the housewrap—is installed over the walls before the windows are installed (housewrap first), or the housewrap is installed after the windows (windows first). If you scan through window-installation articles and videos by Fine Homebuilding and other building resources, you’ll notice that most of them profile the housewrap-first approach. This bias is reinforced by window manufacturers’ instructions. Many present the housewrap-first approach to window flashing exclusively; if they do include the windows-first approach, it’s often deeper in the guide or presented as an alternative.

We all fall into building habits based on what we learned early in our careers and how things are done in our areas. Many home-building practices are regional. The windows-first approach isn’t as widespread as the housewrap-first approach, but in some parts of the country, you’ll find it used regularly.

You may be skeptical of the idea of installing the windows before the housewrap, but it could be an approach that you find helpful when project conditions…