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Re: FNDN: Residential footings considering frost depth

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The frost depth will very depending on whether the building is heated or
not and most importantly how the building is insulated.  If the building
has a crawl space and the foundation walls are insulated and the residence
is heated during the winter then the frost depth can be minimized.  You
should also then not need to worry about frost depth for the interior
footings.  If however the floor is well insulated and there is no
foundation wall insulation then the frost could penetrate well under the
house.  Insulation is an important issue because in most cold regions there
is snow which helps to minimize the frost depth.  Under a house however
there would obviously be no snow cover so the frost depth could actually
increase or decrease depending on the way the insulation is placed.

If the construction is a slab on grade then the issue is of less concern
because you would not generally insulate the floor.  It would however be a
good idea to insulate the perimeter foundation wall.

>I am designing a residential type structure in a climate where there exists
>a 30" frost depth. I intend to design the foundation such that the footings
>go at least 18" below the frost depth for proper bearing. My question is: do
>I only have to do this for the exterior footings or do I also have to do
>this at the interior footings?
>Bill Allen