Exterior Insulation and Window Buck Termination Point
idahobuild
| Posted in General Questions on
Hey All,
Our windows are on there way so I’ve been reviewing the plan details for them. Does it make sense that the window buck and thus the window’s nail flange will be in line with the rain screen furring strips and not with the exterior insulation (see atch’d pics for details)?
Also, for rainscreen battens, would 1×3 work or should we perhaps go with 1×4 to get more ‘wiggle’ room when nailing siding/trim?
Thanks once again.
Walt
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Replies
idahobuild,
If you are using flanged windows the buck should stop in the same plane as the foam.
There are many ways it can be done, none of them necessarily right or wrong. I've done it as you show with no problems; you just have to be very careful that the buck is fully flashed and sealed to the WRB and the air control layer. I almost always place both at the face of the sheathing, which would work with your design if you hold the foam insulation off the buck a bit.
For best performance, and usually-desirable shadow lines, I prefer to nail the flanges to the sheathing and then make exterior extension jambs and sill extension. Both take a lot of thought to provide nailing, drainage and future repair or replacement, but it's possible. I like this solution with what I call fin jambs, which replace exterior casing by projecting beyond the cladding.
You can also do as Malcolm says and stop the buck at the foam. That is ideal when your WRB and air control layer are at the face of the foam, or the foam itself, and also works fine if you tie the buck and window back to a WRB/air control at the sheathing. The built-in extensions on the window exterior will allow 3/4" furring to be concealed and you can use any thickness of exterior casing.
If you're a Prime member, I have a few more details here: https://www.greenbuildingadvisor.com/article/windows-in-thick-walls.
1x3 can certainly work, but as you note 1x4 gives you a bit more wiggle room when fastening siding. Maybe more importantly though, 1x4 is less likely to split when you're fastening it up, so might be worth going wider just to make the furring strip install go a little easier.
I'm going to check the cost delta and see if going to 1x4 works for the budget.
Thanks Paul.
Thanks Malcolm and Michael,
I'll give the Prime detail article a thorough read. Our A/WRB is back at the sheathing layer (Prosoco MVP with Fast-Flash at the bottom).
For the windows, I am thinking that I'll fully build out one window as a mock-up/test. Maybe even with a couple of configurations. At least then we will be able to see how it goes.
Thanks!
idahobuild,
On a related note, I don't think venting the rain-screen above or below windows makes sense. If you keep the battens away from the window frame air can move around it. That allows you to prioritize keeping water out - especially at the vulnerable sill. At the top, keep the trim up over the head flashing 1/8" to provide a drainage path.
I get it. Thanks Malcolm!
If you do go with the window buck aligned with outside of rainscreen make sure you rabbit the head trim as shown in the detail you posted. Otherwise you are making a dam at the top of your window buck.
Nothing wrong with doing that if that's where you want the windows positioned. Depending on your siding and trim choices, it might make things easier to reduce the depth of the bucks by the thickness of the window flange, so the outer surface of the flange is flush with the furring strips.