I plan to use blue board insulation to insulate the footers on a new home we are building. The exterior will be cinder block with a earth berm on the north side and a partial berm on the east side. Is it possible to use the blue board as the form for the footing rather than form it with wood? Obviously after the pour I would just leave the blue board. Seems like it would save time and money but not sure if the blue board is rigid enough or what potential problems I might encounter.

Any feedback is greatly appreciated.

Thanks,
Ladena

Posted By ladena on 05 Jun 2010 12:12 PM
I plan to use blue board insulation to insulate the footers on a new home we are building. The exterior will be cinder block with a earth berm on the north side and a partial berm on the east side. Is it possible to use the blue board as the form for the footing rather than form it with wood? Obviously after the pour I would just leave the blue board. Seems like it would save time and money but not sure if the blue board is rigid enough or what potential problems I might encounter.

Any feedback is greatly appreciated.

Thanks,
Ladena

I am not sure why the footer would need insulation? You  may want to consider using 2x  boards, then stripping the forms and using for door headers and other interior framing.

It would take a substantial thickness (at least 1.5") and temporary support & ties to use XPS as the concrete forms. Look at some of the ICF (insulating concrete form) systems, (made of EPS) which which might be easier to deal with since the engineering is already done for you.

Chris- in much of the northern US (and all of Canada) the subsoil is cold enough to represent a real heating load, and if you're trying to go superinsulated you can't get around insulating the footers as well as the stem walls & slabs. (The slab in my basement never breaks out of the mid-50s, even in summer- in the upper midwest it might not break out of the 40s if left uninsulated.)

Posted By Dana1 on 07 Jun 2010 02:39 PM
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Chris- in much of the northern US (and all of Canada) the subsoil is cold enough to represent a real heating load, and if you're trying to go superinsulated you can't get around insulating the footers as well as the stem walls & slabs. (The slab in my basement never breaks out of the mid-50s, even in summer- in the upper midwest it might not break out of the 40s if left uninsulated.)

Dana1;

I am from Erie, Pa. originally and had built over 400 living units while there, (First Allegheny Const. & Dev. Inc.)  I am quite familiar with -15 degree nights, -60 wind chill and annual snow fall of 120-140 inches. A good reason to drive me south 26 years ago.

I did not think it would do much good to insulate a footer if the slab are in contact with earth/gravel?

Depends on your design goals. If you're going PassiveHouse style, even 50F gravel is too much heat loss through the thermally-bridging gravel. If you're heating the place with a fossil-burner or woodstove, it might take 3-5 decades for footing insulation to net-present-value positive in the financial analysis though (but much quicker with R5 under a slab- less than two decades.) With 40F subsoil it's roughly half the time to pay back. With 60F subsoil, fuggedaboudit. Erie's subsoil temps are right around 50F- you would likely have noticed it more were you building Duluth, where it's fully 10F colder under ground.

If the footing is less than couple of feet above a 50F or colder water table the payoff comes substantially sooner than if it's 10+ feet above the water table. Damp dirt/gravel just isn't much of an insulator, and neither is concrete, and thermal bridges are thermal bridges. (Nobody thinks it's ridiculous to have an insulated concrete wall above grade when it's 50F out, eh?) I have several upgrades with higher priority than my basement slab, but it's on the (maybe, someday) list. A thousand square feet of 52-55F concrete, is a real heat load to the structure, even if it's a background-load that gets swamped by bigger but more variable & seasonal heat loads. Since I have little head room, I'd have to break it up & re-pour to get any R in there, which means it's has very low bang per energy-efficiency-buck. Unless there's a substantial subsidy for it, I'm probably not going there until I'm ready to convert it all to living space with more headroom (which may never happen.)