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Any experience with “frost protected shallow footers”? Here’s a description I heard… “FPSF’s are footers that need only to be 12 inches deep, no matter what the frost-line in your area. They work by insulating the sides of the footer, thus protecting them from heave, allowing them to be so shallow. They are used extensively in Nordic countries. The CABO code for 94-95 first allowed them.”
Good, bad, indifferent? Does code really allow them?
Question 2: Have any of you insulated under a footer? Always, sometimes, never? Code issues? Other concerns?
Thanks. Jim
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Frost protected footers are insulated on the sides of the wall and sideways away from the building for a distance roughly equal to the frost depth of the locale. This insulation is placed under the soil approximately 6". You cannot insulate under a footing because the insulation cannot carry the weight of the structure.
*Slight adjustment......there is insulation that you can and do put under structures much larger than this.Very common under refrigerated buildings.Gabe
*A friend who's done a LOT of construction over maybe 40 years--residential, bulk storage, schools and gymnasiums--just wrote the following to me about this: "A good 2 # urethane foam has a compressive strength of 30 psi. multiply 30 times 144 and you get 4320 psf. That is as good as ground in most places. If you go to 3# foam it will hold about 50% more." Is this consistent with your experience, Gabe? What structures qualify or don't qualify? And since it would create a complete thermal break for the structure, why wouldn't every building that benefits from foundation insulation, also benefit from under-footer insulation?This is new to me, so I'm trying to learn its limits. Thanks.
*I guess it would depend on what you want to accomplish.I've only used foam under buildings that were kept refrigerated. One specifically was used to store tree seedlings in a dormant stage and with our winters here, there is a danger of perma frost forming under the building and doing damage. By using the foam under the footings and walls this was prevented.Most building that have foundation walls below frost level also benefit from the stable temperatures of the ground helping to heat in the winter and cool in the summer.There would few times where you could justify the cost of high tensile styrofoam under most buildings. We routinely put sm around shallow walls to prevent frost from getting under the footings and heaving them. You would have to design the building to use foam as well. No such thing as a perfect thermal break. Eventually temperatures balance out.Just think as thermal resistance as just that....resistance.....and not thermal proofing.Gabe
*>And since it would create a complete thermal break for the structure>Just think as thermal resistanceYou're right, of course. I should have said create a better thermal break. For all the times I've told people that R-value is Resistance and not Prevention, I shouldn't have implied that myself.I wonder where the break-even is for under-footer insulation...Thanks. Gives me something to think about.