How many inch wider the bottom frost free fill than the footing?

[chrislaope]

Hi, everybody'

I have a simple question to ask:

To prevent frost heave, the contractor is digging a wide trench to back fill frost free material, my question is how many inches (feet) wider do you usually specify for the frost free fill (or the trench) than the supported footing?

Thanks.

 

[larsacious]

Frost heave is typically a matter of footing depth and not width.

 

[chrislaope]

Yes I know that, so do you mean the trench can be digged same width as footing, no need to be a little bit wider?

Thanks

 

[Splitrings]

I would suggest looking at ASCE 32, "Design and Construction of Frost Protected Shallow Foundations".

 

[BAretired]

It is usual practice in my area to construct the footing below frost level or to insulate so that frost cannot get below the footing.

Our frost penetrates about five feet next to a heated building, six to eight feet in open terrain.

BA