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“With the right materials on hand, flashing a newly installed window should go smoothly. But what about an existing window that needs re-flashing when, say, the house is being resided. What’s the best approach?”
For both new and existing windows, the goals are the same: layer materials in the assembly so they direct water out and away from the house, and provide a path for any water that does get in to escape.
New windows can be installed in one of several ways. In this video, veteran builder Rick Arnold explains two approaches for integrating the water-resistant barrier (WRB) with the window flashing to prevent leaks. In one approach, the WRB is brought just inside the rough opening where it is taped to the framing. Alternately, the WRB can be cut back from the edge of the rough opening so the window flange is fastened and sealed directly to the sheathing. The WRB is joined to the window flange with flashing tape. Either way works.
When you’re flashing a window that’s already in place, the same fundamentals apply.
Start with the sides of the window by applying flashing tape over the nail flanges. The tape should extend several inches above the top of the window frame, and several inches below the bottom of the window frame. Arnold recommends the tape lap up the side of the window frame slightly—about 1/4 inch or so—to protect the vulnerable seam between the window frame and the nailing flange. Pressure-sensitive tape should be rolled out with a J-roller.
Next is the top of the window. Make an angled cut at each upper corner of the window and fold the WRB up and out of the way. Apply a strip of flashing tape over the nailing flange to seal the…
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5 Comments
Very helpful, thanks!
I would love to see an expansion on this topic.
In Chicago where we have more than our share of bad weather, 95% ar existing. Many of the homes are decades old with a variety of wall assemblies. Triple wyeth walls, Stucco with box car siding. and frame houses with wood clapboards and empty wall cavities. Old isn't 10 years, old is 100 years.
Thanks for the great article.
I found that it works a lot better leaving it stick out a little bit from window so water drips off rather running down the wood of window trim the paint holds up way better on the window.
GreenBuildingAdvisor: https://www.greenbuildingadvisor.com/article/replacing-windows-on-a-1980s-farmhouse https://slope3.io
Are there any steps you'd recommend for a 200 year old wooden window (in great shape) if the interior of the room is gutted down to the framing? Would wrapping the wooden box in flashing tape be recommended to help airtightness even if it can't extend past the exterior sheathing?
By "box" I assume you mean the window frame? Taping the corners could help but intact wood is airtight so I don't see a reason to wrap everything. The biggest air leaks at old windows, by far, is between the sash(es) and frame. There are various ways to improve that leak point. Otherwise I would stuff some fibrous insulation in the gaps and tape the interior with a vapor-permeable, airtight tape.
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