Depth of Interior garage footing

[nhstruct]

I am looking for everyone opinion on the proper depth for the interior footing in an unheated garage. We do many apartment buildings where the basement is a parking level. The perimeter wall is designed to be 4'-0" below grade minimum (standard frost depth of the region), however the footings at the interior garage we typically set so the top of footing is 1'-0" below the top of slab. When we do design the interior footing to be 4'-0" below the top of slab the contractors and architects get upset and we generally move them back up. So the question is should these interior footings in an unheated space meet frost depth, or are they acceptable to be high.

Thanks in advanced

 

[BadgerPE]

Typically, if it is unheated and uninsulated, I will require the footings to extend to frost depth. However, often times we design buildings that are insulated but unheated and attached to a secondary structure which is heated. In those situations, I find it hard to believe that the frost will penetrate all they way to an interior column and be severe enough to cause displacement. However, it may depend on how large your unheated structure is as well. Don't forget to check uplift on the column, and that may be a way to justify an increased depth of footing without getting into the frost issue.

 

[dik]

All you need is the door to be open for awhile... frost will not likely penetrate to the frostlevel depth... but, you will have difficulty researching to find out how deep... and the time involved will likely be more costly than digging the extra couple of feet... we could be liable, and we are not being paid to enter a 'cardgame'. We also use extruded polystyrene insulation (Type 4) in our local to achieve frost cover...

Dik