On a 11 1/4" ICF thick wall, if the windows are set to the interior, this creates a nice recessed look from the exterior. Architecturally, the inset windows really enhance the exterior and the stucco can nicely wrap the corner and butt into the window frame.

1 - Do most window manufacturers allow for this type of install?

2 - With this type of install, the use of a nailing flange is eliminated, correct?

3 - Are there any "downsides" to this type of install?

4 - One would have to attach the window frames by utilizing the screw through the frame method or attachment brackets, correct?

5 - Can one still use vinyl window bucks with this method?








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Architecturally, the inset windows really enhance the exterior

I think that is a matter of opinion and maybe dependent on the design style as well. I didn't want the "blockhouse" look, so the windows are flush with the outside.

3 - Are there any "downsides" to this type of install?

Right off the bat, I'd say it appears that setting the windows in unnecessarily increases the exterior surface of the home and exposes more of your ICF wall to the exterior.

Posted By Lbear on 29 Apr 2012 04:26 AM
On a 11 1/4" ICF thick wall, if the windows are set to the interior, this creates a nice recessed look from the exterior. Architecturally, the inset windows really enhance the exterior and the stucco can nicely wrap the corner and butt into the window frame.



2 - With this type of install, the use of a nailing flange is eliminated, correct?

It is possible to eliminate nailing flange if desired, but not necessary.  I'm doing essentially the same for my windows on the back of my ICF home.

If you make your window buck 3" wider and 4.5" taller than the window rough opening dimensions, you frame inside the window bucks after the concrete is poured with 2x4 or 2x6 all around setting the 2x flush with the inside edge of the ICF foam.  On the bottom, you install two (2) 2x4 or 2x6, preferably treated lumber, so that you can create a slope to drain water away from the window.  This will create a nailing flange near the middle of your ICF wall.  Your typical window nailing flange is 1-1/4", so you can attach your window to this interior 2x framing.  I would use RTV silicone to seal the interior wood framing to the window buck to eliminate any wind or water leaks.  I would also recommend that you install 1" of rigid foam insulation strips over the outside of this 2x before you attach the window to minimize the thermal short circuit caused by the internal wood framing.  Silicone seal all seams in rigid foam and install waterproofing membrane at bottom of window framing to insure that any water that might get through drains to the exterior.  Apply a bead of silicone to the face of the rigid foam, install window, then nail or screw the window flange through the rigid foam into the internal wood framing.  If you are doing stucco, then you would come back with ~1" thick EPS foam to line the outside part of your exposed window buck for thermal insulation as well as a bonding surface for the stucco.  This will cover the window nailing flange and bring the stucco up near the face of the window.  This exterior EPS would go from the face of the window flange to the outside edge of your ICF foam.

Does anyone have a link to see pics and what the detailing would be like on an interior recessed window with a 12" thick wall?

In my case this will be interesting as I'm looking at Quad Lock's 4.25" exterior foam thickness. I don't want the "block" look but you can't install the windows on the foam... I figure a really strong buck is needed.

Posted By ErVikingo on 30 Apr 2012 09:12 AM
In my case this will be interesting as I'm looking at Quad Lock's 4.25" exterior foam thickness. I don't want the "block" look but you can't install the windows on the foam... I figure a really strong buck is needed.

Depending on your concrete core thickness (I assume 6"), your wall thickness is over 13" thick. Even if you install the windows centered, you will have 5" of sill area both indoors and out. If you install the windows flush on the outside you will have a huge window sill on the interior. Plus as you mentioned, mounting flush will not the best solution as a window sitting on top of EPS is not as stable as it sitting on top of the concrete core. The heavier the window, the greater the chance of deflection if the window is sort of "cantilevered" on the wood buck.

Ideally you want the window to sit mostly on the concrete core area.

Talk it over with your architect and window manufacturer. Aesthetically speaking, most architects like recessing the windows towards the interior. Even on my current home they mounted the windows flush (wood frame) but they installed stucco/EPS "popouts" to break-up the flush window look.

Structure wise, there is not much difference if you use a full treated buck. Aesthetically they look better mid mount, however you will need to get your measurements right for the extra needed for the additional 2x materials. Flashing can be a little more work to get it right depending upon the type you are using. Refer to the engineer for mounting flange or non depending upon your location.

I always use flange windows with 1 x bucks (2 x sub bucks) and CastCrete Sills.

Less is more in MHO. Easier to seal, less wood.

Whatever you do, don't use cheap caulk/sealant.

Here is a link to a technical drawing from Quad-Lock showing the attachment of shutters directly to concrete. A similar theory could be applied to installing your windows flush to the outside of the wall.

http://www.quadlock.com/technical_library/drawings/pdf/07.8.1.pdf

The heavier the window, the greater the chance of deflection if the window is sort of "cantilevered" on the wood buck.

Ideally you want the window to sit mostly on the concrete core area.

No need to do that. I have huge windows on full 2X treated bucks. They do not "cantilever" as they are supported by foam with a compressive strength of 25 psi. That is more than enough to support any window you want to put in there without having to worry if the window is situated above concrete.

Posted By ICFHybrid on 06 Jun 2012 08:38 PM

The heavier the window, the greater the chance of deflection if the window is sort of "cantilevered" on the wood buck.

Ideally you want the window to sit mostly on the concrete core area.

No need to do that. I have huge windows on full 2X treated bucks. They do not "cantilever" as they are supported by foam with a compressive strength of 25 psi. That is more than enough to support any window you want to put in there without having to worry if the window is situated above concrete.

I was told that the EPS in ICF should only be viewed as insulation and never used as a structural item but then again, I guess it is somewhat structural as it holds back the concrete as it is curing.

I personally dislike "innie" windows both for looks and it complicates flashing and sill details. (so no, architects do not aleays prefer it this way ) As ICFH mentioned, EPS has good compressive strength (I am not sure the type typically used in ICF...II I assume?)
On a project I did last year we had some large windows. While I designed the buck to be inset inside the foam, the engineer thought it would be a good idea to cut the outer foam 1.5" less then the inner and set the face of the 2x flush with the exterior of the foam and flush to the inside of the inner foam. This gave the builders solid nailing and allowed them to spray foam the buck to the foam around it. They set the flanged window and taped it off.