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Re: FNDN: Residential fo

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I would tend to put the foundation well below the frost line as Bill Allen is 
considering.  After all, how accurate is "frost depth" anyway?

While frost depth is not a consideration in most places here in Arizona, 
there are mountain locations and higher elevations where frost depth 
is/should be a consideration.  When I have contacted agencies such as the 
Soil Conservation Service, Forest Service and Weather Bureau, as well as 
building departments, to find the frost depth in certain areas, they acted as 
if they didn't know what I was talking about.  As a result, I use a minimum 
footing depth of 48 inches where frost depth is unknown and I know that the 
ground will freeze.

If the building is a slab-on-grade residence, then I would not see any need 
to extend the interior footings below frost depth.  However, if the first 
floor is elevated and the area under the floor is well ventilated or open so 
that the temperature in the underfloor area can go below freezing, then I 
would also extend the interior footings to the same depth as the exterior 
footings.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona