Window installation with 2 inches of outsulation: best techniques and approx. added cost?
If we add ~2″ of insulation outside the sheathing, what are the best options for window installation? I’ve seen a couple approaches on the site but couldn’t find a comprehensive article or recommendation. What I’ve seen is generally a) tape nailing fin to outside of insulation, screw jamb in to wood, but not sure if jambs are deep enough or b) install to sheathing like normal, buck-out windows. If using Zip-R, nailing flange to the Zip OSB. Not sure if I captured everything, but also, what other considerations are there and what’s the added (material/labor) cost.
Also, if the drainage plane is on exterior of insulation (where the rainscreen is), and window is installed to the sheathing where does water from the weepholes in the window go?
Thanks
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I did something similar to B on my current build.
I bucked out the window frame with 2x4 on the flat and 1/2 ply to make a total of 2 inches. it's not the most energy efficient as it's an extra 3.5" of wood thermal bridging, but my window guys weren't the most knowledgeable and it got the job done.
They used blueskin around the inside of the opening and nailed the window flanges on top of the bucks like you would a normal window install. I 3M taped the bluskin to the rest of the buck to the sheathing and transitioned the wrb on top of the window flanges with more 3M tape (leaving to bottom to allow for egress when the window leaks). I also back caulked the bottom of the window at the inside since they refused to slope the sill.
I was really worried about it when I first was doing it. But in the end it was pretty simple. the extra effort was just framing the bucks and bit more tape. Also, don't forget about your inside detail, whether you get jamb extensions when you order the windows or do some sort of return.
That's just my build though, there are lots of people on here that will geek out on fenestrations and give much better advice.
Thanks, this is helpful! Was that for 2" of insulation or more/less?
K.T.,
Q. "I’ve seen a couple approaches on the site, but couldn’t find a comprehensive article or recommendation."
A. Here is a link to the comprehensive article you are looking for: "Installing Windows In a Foam-Sheathed Wall."
Super helpful, thanks! Unfort. it doesn't let me see the whole article (Prime required).
Any similar sources, i.e. buildingscience, finehomebuilding?
I did get as far as the photo, it looks like 2x3 or 2x4 lumber on edge is used. With 2" foam + furring strip/rainscreen and cladding, I'm up to about 3". Should the window frame buildout be proud of the cladding or below or does it matter.
If you are building a house, a paid subscription for a month or two here is well worth the cost for full article access.