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Window flashing with exterior rigid insulation

I operate in climate zone 5B which has about 6,600 HDD. Homes built here generally do not require cooling systems -- only heating. My question has to do with where the water resistive barrier should be placed on the construction detailed below:

Form the inside out:
1. 1/2" sheetrock
2. 2x6 framing filled with dense-packed cellulose insulation
3. 7/16" OSB sheathing
4. 2" XPS rigid insualation
5. Jumbo Tex-type WRB -- bassically 2 layers of 15# impregnated roofing felt
6. Stucco wire
7. 3-coat stucco system

My thinking is that the flashing, particularly the bottom window flashing, should extend from the window nailing fins over the 2" XPS rigid insulation and then down between the two layers of Jumbo Tex WRB. My thinking is that the 1st layer of the Jumbo Tex bonds to the back of the stucco system so any moisture should be allowed to run down between the 2 layers of Jumbo Tex.

Is that right?

Asked by Steve Vollstedt
Posted Feb 3, 2011 4:14 PM ET
Edited Feb 3, 2011 4:38 PM ET


2 Answers

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Hi Steve,
Why wouldn't you extend flashing out beyond the stucco? There may be a good reason.. but I can't come up with one.

Answered by Chris Koehn
Posted Feb 3, 2011 4:36 PM ET


You can install your windows as "innie" windows or "outie" windows. (If you are unfamiliar with those terms, see ‘Innie’ Windows or ‘Outie’ Windows?)

If you want to install your WRB on the outside of the rigid foam, I suggest that you install your windows as outies.

Answered by Martin Holladay, GBA Advisor
Posted Feb 3, 2011 4:37 PM ET

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