Hi, all. I'm considering ICFs for the front wall of my new house, but my home designer is recommending stick construction instead. I'd like to describe the design (it's earth-sheltered and passive solar) and ask if you think ICFs would be a good choice, please. The house is a 2000 sq ft bungalow (including the garage), a trapezoid with the front width = 68', the back width = 52', the right wall (at 90 degrees) = 34' long, and the left wall (at 64 degrees) = 37' long. The roof is a single plane cathedral with 1/12 slope, 10'-6" high at the front dropping to 7'-8" at the back. The house is like a walk-out basement -- it's slab on grade with poured-cement side and rear walls, with high-drainage soil bermed right up to the roof on the side and rear walls. The roof is a green one, continuing the berm up onto 2-4" of soil (over Bituthene, insulation, root barrier etc.). The front wall faces south with all the doors and windows. It's a cold climate, central Ontario, much like Minnesota, so I'm aiming for an R40 front wall. So, are ICFs a good choice for the front wall, given that it's got windows and doors in a high percentage of its area? My concern is that I'm thinking of three big window holes, each 6' high and 10' wide; would ICFs go above that span? And does that pose problems supporting the heavy roof load (perhaps 80 psi)? If I switched to several smaller window holes instead of three 10' wide ones, what is the minimum width ICFs require between window frames? Thanks for your thoughts, ...Terry

Yes, ICF walls can accommodate those openings if the lintels are properly reinforced. I've got a 9' garage door opening in my basement wall.

With a 10'+ high wall and normal height windows (6'8"), you will have a lintel depth >36" which makes lintel design easier.

Another option for multiple windows in a large opening, say three (3) 3'x6' windows side by side, is to provide two (2) 2x6 or larger wood studs between each window to help transfer the load from the header above to the footings. This is what I am doing in my dining area wall.

This pretty much explains what is required:

http://www.huduser.org/Publications/PDF/icf_2ed.pdf

It's not unusual to go 20-25 feet. Your typical ICF manufacturers lintel tables go up to 20 feet. Re: situation where you have minimal concrete between windows (say < 9") ... one rule of thumb seen is the engineer will design a lintel accross the opening as if columns were NOT present at all. For example, 20' opening with a couple of small concrete sections between three windows -- ignore the concrete (or wood) and design the lintel for full 20'.

Regarding the 80 psi -- did you mean 80 psf? 80 psi is 11,520 psf. 1500 lbs per linear foot is quite easy to attain with ICF (across the opening). Regards.

Just wondering why you would not use ICF for the earth bermed walls as well?

Thanks, arkie6, for the info and for the PDF reference. It's over my inexperienced-owner head but it lets me know what's possible. ...Terry

Thanks for your response, TexasICF. I'd prefer a 2' casement + 6' picture window + 2' casement all in a single fiberglass frame, rather than break those up with vertical 2x6's as arkie6 suggested. The latter might be safest but I imagine there's more thermal break. Yes, I did mean 80 psf, not psi -- thanks for catching me. ...Terry

Hi, vanman2004b. I'm not using ICF for the earth-bermed walls because I need the blueboard to be on the outside of the concrete only. This way the insulation traps heat loss from inside the house but it allows the earth's 50 F constant temperature to make its way inward, reducing winter heating and summer cooling costs. The exposed concrete walls (plaster covered rather than drywalled) also soak up solar heat entering the front windows, as thermal mass. ...Terry

Terry, you know another option for your earthen bermed walls is LiteForm ICFs with the strippable XPS panels. These forms use 2" thick planks of XPS foam 8"x48". After the concrete is poured and sufficiently cured, you can strip off the interior XPS and then glue it on the outside if that is your desire. Check out their website for more info. They can also give you a materials quote online.

A 2x6 is going to have a better R value than your windows unless you go with uber expensive ultra low U value windows.

Softwood lumber (spruce, pine, etc.) has an R value of ~1.25 / inch.  For a 5.5" wide 2x6, that's an R value of ~7.  There are very few windows that can top this R value.  Most moderately priced double pane insulated windows with low E coatings typically come in with a U value of 0.35 to 0.25.  That's an R value of 3 to 4.

http://www.coloradoenergy.org/procorner/stuff/r-values.htm

One more thing regarding the double 2x6s between the windows. If you set the 2x6s 2" back from the outside edge of the ICF foam, then you can cover the outside edge of the 2x6s with 3" wide strips of rigid XPS insulation prior to nailing/screwing your windows to the frame work. That will give you an additional R10 at 2" of XPS. If you go with 2" of XPS over the studs, you would most likely want to use 3" screws to attach your window nailing fins. Another advantage to this approach is that it puts the 2x6 studs more towards the center of the wall and provides better structural support. A disadvantage to using the 2x6s between the windows is that it will require additional trim or finish work on the inside and outside at this joint between the windows; although, I don't consider it any significant issue.

You're right, arkie6, about the R-values, and I like your suggestion of setting the 2x6's back to add insulation in front between the windows. Thanks also for introducing me to LiteForm's removable insulation -- moving the inner foam to the outside makes ISFs now a viable option for me. I'd have to cut off the protruding plastic forming ties but that shouldn't be a problem. And while I don't know anyone in my region with LiteForm experience, they should be easy to handle for anyone with any ICF experience, I imagine? So now, for all four sides, I've just got the standard pros and cons of ICFs (higher costs) vs standard forms (slower construction). Thanks again, ...Terry