BY RANDY WILLIAMS
5 tips for successfully installing windows
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.
I write a lot about the four control layers every building envelope has. There is an order of importance:
- Water control layer
- Air control layer
- Vapor control layer
- Thermal control layer
A window needs to be able to perform the functions of all four control layers in order to be successful. Window manufacturers design their units to be effective at controlling the movement of water, air, vapor, and heat through good product design and manufacturing techniques, but where they lose control is in the installation of the window. Often the success or failure of a window will come down to the installation, but there are ways to avoid some of the window installation failures I’ve come across.
1. Where possible, design the building to limit a window’s contact with water
If you design a roof with large overhangs, or use an awning above a window, the part of the window that’s most exposed, the window head, doesn’t get wet. If it doesn’t get wet, it can’t leak water, which is one big problem solved. Another common problem is when an adjacent roof overhang is directly above a window. This is where a kickout flashing can be a good solution. A kickout flashing is a manufactured or site-built way to divert water away from the wall surfaces (and any building component below) where the slope of the roofline meets an exterior wall.
A design that incorporates an overhang above a window can help protect the most exposed part of the window, the window head, from water.
2. Always use a drip cap
A missing window head flashing is one of the most overlooked details I see. The idea is to keep water moving so it can’t find a place to sit. If it sits, there’s a chance it can find a hole and end up inside the building. A drip cap with a slight pitch towards the front of the window is effective at keeping water moving.
3. Shingle lap to direct water down and out
We’ve been good at keeping roofs from leaking for a long time. We do this by lapping roofing materials over the lower courses — simple and effective. This works around windows and doors as well. Lap the courses of water resistive barrier (WRB) above and over the courses below, and lap over the top of the window. Nowadays, there are some newer sheeting products with integrated WRB that rely on tapes to prevent water from ending up someplace it shouldn’t. In those cases, the key is to follow the sheeting manufacturer’s instructions — i.e., roll the tape!
Use the lapping technique around windows and doors to help keep water out.
