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Tyvek detail around windows

Help, the windows are here! so i'm all geeked out to check them out and install them. we wrapped the entire house, including the rough openings, in tyvek, BEFORE the windows arrived. our plan was to cut open the wrb, flash the sill with a piece of bevelled siding and flexwrap, then install the window. tyvek recommends making an i-cut in the wrb (one vertical cut in the middle from header to sill and two horizontal cuts from side to side along the header and sill) and wrapping the flaps of the tyvek around the sides of the window and fastening them. my thought is doesn't this invite water to migrate into the house? why not just cut the wrb to the actual rough opening dimensions? thanks again...

Asked by erik olofsson
Posted Dec 5, 2012 12:12 PM ET
Edited Dec 5, 2012 1:06 PM ET


3 Answers

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There is more than one way to flash a window opening. Here's the overarching principle to keep in mind: you are flashing the rough opening, not the window. If the rough opening is waterproof, you're good.

That means that the rough jambs need to be protected with housewrap or some type of flexible flashing. The rough jambs need to convey water to the sill pan flashing. The sill pan flashing needs to be sloped to the exterior or to include a back-dam (or both).

If you don't want to cover your rough jambs with housewrap, you still need to cover them with something waterproof. The jambs are part of the rough opening, and it all has to be flashed so that you are prepared for the day when your windows begin to leak.

Answered by Martin Holladay, GBA Advisor
Posted Dec 5, 2012 1:04 PM ET


thanks again, martin.
because we used larsen trusses, we had to employ osb window bucks making the rough openings about 12" deep. would you recommend waterproofing the full 12"? the sills have bevel siding and flexwrap to provide slope and waterproofness but even this only projects into the rough opening 3.5" of the 12" RO depth...

Answered by erik olofsson
Posted Dec 5, 2012 3:56 PM ET


Well, if you haven't cut the Tyvek yet, it's simple enough to cut the Tyvek in such a way that you can fold it back to cover the jambs of the rough opening.

If you already cut out the Tyvek the wrong way and put the Tyvek in the dumpster, you could use another product -- for example, asphalt felt -- as long as you maintain your laps properly and fold the product around any unprotected corners.

Answered by Martin Holladay, GBA Advisor
Posted Dec 5, 2012 4:12 PM ET

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