Do I need a window buck or picture frame?
Sam2112
| Posted in General Questions on
I’ve got two inches of polyiso on my 2 x 4 walls, and the Andersen windows with nailing flanges that we order just arrived.
My contractor wants to install them as outies and just nail through the foam. I know you can pull this off with less thick foam, but is it possible for windows to hang just from the flange with two inches of insulation?
It was hard enough to convince my contractor to go with the exterior insulation, and most of his crew doesn’t speak English, so I’m trying to keep this as simple as possible.
Thanks!
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Replies
Won't window bucks shrink the rough opening size?
I'm assuming the walls are already framed and windows ordered.
A buck would, but not a picture frame in the exterior. Everything is framed and the windows are in.
Sam,
With 2" of exterior foam, at the least you will need something at the sill to help bear the load. That could be a solid extension of the sill, or blocks every so often. With that you might be able to get by with just nailing through the foam on the jambs and head.
How are you dealing with fastening the cladding and trim?
Vinyl siding is getting nails through the foam with 3" nails. Joseph Lstiburek has used just nails for up to 1 1/2 foam, and I was wondering if we could get away with it for 2". Maybe using a few 3 1/2" screws as insurance.
Is the foam detailed to be the weather barrier? The window flange needs to be tied to the weather barrier or the window will leak.
Yes the foil faced foam is the weather barrier.
I doubt that would meet installation requirements for a warranty. I recommend using either solid bucks or ThermalBucks: https://www.greenbuildingadvisor.com/article/windows-in-thick-walls
I'd worry not just about nailing through the insulation (which I don't recommend), but how one would flash this correctly. If the rough openings can accommodate it, the Thermalbuck may be the best choice. It is pretty important to have these details worked out prior to installing windows, flashings, rainscreen and siding. If the control layers aren't continuous one can end up with water entry and degradation issues that kinda make the benefits of the exterior insulation moot. Michael's article is a great resource along with Randy William's recent blog post. https://www.northernbuilt.pro/where-to-locate-the-wrb-when-using-continuous-insulation-inside-or-out/
The WRB is the exterior of the foam and the windows would be installed as outies, so flashing goes on the foam. That being said, it seems like everyone is pretty against nailing through foam so I'm thinking that we just picture frame it.
By "picture framing," do you mean a solid wood buck? I have also seen 1x wood rain screen furring placed over the foam around the window; I thought that was what you meant by picture framing.
Give this a read.
https://www.greenbuildingadvisor.com/article/nailing-window-flanges-through-foam
I've read it. I was looking for people's experience.
I do not know what flavor of Anderson windows you have but that the time to look up the installation instruction. They will be very clear about how much foam you can nail thru. If they do not show foam in the instructions zero is allowed.
https://edge.sitecorecloud.io/andersencorporation-c47i754m/media/Project/AndersenCorporation/AndersenWindows/AndersenWindows/files/technical-docs/installation-guide/installationguide-0000632.pdf?rev=f5e3b3c1c60646aca0d900c1fe819438
You will need to provide solid wood behind the nailing flanges.
Walta
I absolutely would not attach through 2 inches of foam. People do it but I think there's a lot of risk and the long term deflection of the material may become a problem down the line. It's very easy to picture frame with 2x2 material if you have 1 1/2" of foam. With 2" you need to rip pieces to size.
Picture frame the openings with 1 1/2" x 2" material that gets taped to the foam face and into the opening, at least 3 1/2", so that the edge of the picture frame, the wall sheathing and some of the jack stud is covered. This completes your WRB before the window install. Then tape over the jamb flanges and over the header flange, in that order. Install a metal header flashing and tape over that as well. I am not going to get into sill details here. Too many ways to do it. This is the kind of thing that should be detailed into the drawings even before permits are pulled. You may want to look ahead, now, to what other details need attention like this.
I appreciate the good info!