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Exterior foam insulation and window buck question:

ArayaHomes | Posted in Energy Efficiency and Durability on

Hi everyone! Some techincal questions for you. Some of my details might need a bit more cleaning up, I’m aware of that, curently trying to solve the following:

Some of the parts of my window assembly, you’re looking at a plywood box buck extending from structure to exterior face of foam, it is liquid flashed from interior all the way around the box to the outside face back to the building against the wrb, drainage matt infront to provide capillary break for exterior foam. I’ll provide a photo of that in photo 3. There’s quite a bit more details behind the assembly that you can’t see but that detail provided should be good enough for my questions below..

1.) Do you think insulating against the window as shown here is worth it? Here’s the video example

Can anyone give advice on if that insulation is really worth it? Hammer and hand says 15% savings overall heating demand in a year, that’s pretty good to me for designing performance homes as I do.

2.) Photo 1:

I’d also like to know about exterior insulation sealing. I am leaving the top and bottom horizontal foam to buck joints untaped, in the event that water needs to get out, but would it be better in this case to use highly permeable tape to cover that joint in the red circle in the photo and the top of window as well, cover those up with vapour open peel and stick joint tape?

3.) Photo 2:

I have seen a number of times and including one of joe lstibureks articles that the head flashing on the window doesn’t need to extend to the face of the foam like I have it or behind the foam to the wrb if that’s where the wrb is (on the sheathing plane), he says for example installing the flashing against the rainscreen is good enough, I don’t agree at all as that’s where water would migrate and rest ontop of the window jamb extension at teh head, in my phoot I atleast tape it to the foam and now if water drips behind the cladding at top of window, it’s directed out instead of pooling on the top of jamb extension at head… What do you guys think about that and I wonder why he recommends it’s not necessarry to make flashing atleast go back and cover the top of jamb extensino head like I have it in my photo.

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