Flashing window bucks for outie windows with drainage plane at sheathing
I’m about to start re-siding my house. I’m stripping it back to the original sheathing boards (ca. 1885) and am going to use 7/16 Forcefield sheathing (Georgia Pacific’s version of Zipboard) over the original sheathing. Then, I’ll add two inches of rigid foam in two layers before siding.
The trick is sorting out window bucks. The following video has provided me some general guidance on it, but I’m still sorting out details about how to flash:
https://www.protradecraft.com/detail/outie-window-details-walls-thick-exterior-insulation
I note in the video that while they called for Z-flashing at the header, but only to the inner layer of the foam sheeting.
i imagine this follows the idea that foam itself has very low permeability. I’ve researched it enough to conclude that WRB over foam seems largely useless (apart from maintaining a continuous drainage plane) which is why I have it at the sheathing level.
i realize the practices in the video create a discontinuous drainage plane, but frankly, I don’t see how the sheathing would ever see moisture in this case, unless the roof overhead leaks down into the framing.
Anyway, I know what best practices are, and my thought was to tape flash the bucks to the sheathing (I’m using solid bucks), but the more I think about this example, I find it hard to see a real problem, aside from its not likely to meet code regarding WRB / drainage planes.
Any thoughts?
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I just wrapped Vycor tape around the bucks back to the sheathing. Even though I taped the foam board seams, I treated everything outside of the zip drainage plane as well, outside. So the siding had flashing, but the foam just sat on the Vycor.
Out of curiosity, how did you attach the foam board to the sheathing?
I used a few screws with plastic washers, then laid 1x3 strapping on top for the rain screen. For that I used either HeadLok or GRK structural screws attached through the foam and sheathing to the studs, at 24" o.c.