Frost Depth 2

[StructuralAddict]

The following is from 2014 New York City Building Code. Does this requirement apply to interior footings in the building? Or just for footings adjacent exposed grade?

"1805.3.1 Frost protection. Except where otherwise protected from frost, shallow foundations, pile caps, and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
1. Extending a minimum of 4 feet (1219 mm) below the lowest adjacent permanent exposed grade"

 

[jayrod12]

I would consider an interior footing inside a heated building as adequately protected from frost. They say by one or more of the methods. Being inside a heated building would be a method if you ask me.

 

[phamENG]

I agree with jayrod, as long as the architect's insulation detailing also agrees. If you've got no insulation on the exterior foundation wall and thick under-slab insulation between said footing and the heated space, the argument starts to get a little thin. (Probably a rare scenario, though.)

 

[StructuralAddict]

Thank you. Per Sec 1805, the minimum depth is 12" from the undisturbed ground surface. I feel that the interior footings of heated buildings are protected from frost (So, the 12" min can be applied). However, I'm not sure if there is a clear statement about that in the code or another reference justifying my "feeling".

"1805.3 Depth of footings. The minimum depth of shallow foundations below the undisturbed ground surface shall be 12 inches (305 mm). Where applicable, the depth of shallow foundations shall also conform to Section 1805.3.1."

 

[phamENG]

Do you have a slab on grade? If so, consider this: if the soils below the slab are allowed to heave the same amount of those outside the building, what does that do to your floor? So that suggests that under the heated building, you're fine. The soil isn't going to heave. This is one of the reasons insulation is typically run from the bottom of the footing all the way up the exterior wall. It helps keep the heat in and under the building.

 

[StructuralAddict]

Thanks phamENG. that's excellent food for thought.

 

[geotechguy1]

I don't know specifically about the New York building code but in Alberta, Canada the logic phamENG shared was pretty standard. Interior footings are considered frost protected for a building expected to be continuously heated, only the exterior footings would require full depth. That being said have to be careful about buildings that might have long construction periods and end up not heated through a winter while construction is underway.

 

[BigH]

Also consider if the "heated building" will be on a "active" soil - will the heated building cause the material below the floor slab to shrink? Opposite effect of ice rinks.