Frost depth for turndown slab
Frost depth for turndown slab
(OP)
I have virtually an unheated metal shack. It will sit on a slab on grade with a turndown. Is is necessary for the turndown to bear below the frost depth? In my mind, only unheated bearing foundations should be below the frost depth. Even though the shack will put load on the turndown, the load is minimum. Any thoughts?






RE: Frost depth for turndown slab
Garth Dreger PE
AZ Phoenix area
RE: Frost depth for turndown slab
For sheds and unattached garages, it is common practice to use a slab on grade with a thickened edge all around the perimeter. The edge thickening is completely within the active zone of frost. If the underlying soil is frost susceptible, say a clay, heaving may be expected during the winter season. If heaving is uniform, it may not be noticed by the occupants, but if the moisture content is variable, the magnitude of heave can vary from one place to another. In buildings of this sort it is prudent to avoid rigid materials such as drywall because it is susceptible to cracking. The perimeter beam is usually reinforced to spread uneven settlement over a broader area.
For residential or commercial buildings, it is common practice to provide foundations below the frost depth in order to avoid the unsightly aspects of heaving.
BA
RE: Frost depth for turndown slab
RE: Frost depth for turndown slab
Dow makes below grade insulation in various compressive strengths for this application.
DaveAtkins
RE: Frost depth for turndown slab
CarlB... I generally place the insulation closer to grade... about a foot down to take as much advantage of the geothermal heat and to provide some measure of protection.
DaveA... I spec the DOW, Type 4, extruded polystyrene almose exclusively... great product. DOW also has a bit of a tech blurb on the use of insulation for geotech info...
Dik
RE: Frost depth for turndown slab
The soil in the Edmonton area is predominantly clay. Geotechnical Engineers sometimes classify it as highly plastic, but I don't think it is as plastic as the clay in Winnipeg. I have heard that Saskatchewan is even worse.
Most engineers tend to avoid shallow foundations because of frost movement, but for a shed, perhaps a little frost heave is not such a big deal.
Retaining walls are also an issue. Some say the foundation should go below the frost line, but that makes it so expensive that most retaining walls are founded in the active zone. When that is done, the wall should never be tied rigidly to a building with deep foundations.
BA
RE: Frost depth for turndown slab
Agree... and even with well founded retaining walls, I don't tie them into real structure.
Dik
RE: Frost depth for turndown slab
You may call me anything you wish. Bart is okay, but my real name is Bruce...Bruce Alexander, sort of like James...James Bond, but I have not had the same success with those of the opposite gender...I wonder why? Any hints would be appreciated.
BA
RE: Frost depth for turndown slab
BA
RE: Frost depth for turndown slab
BA
RE: Frost depth for turndown slab
Maybe instead of saying "Bruce...Bruce Alexander," you should be saying...
"My initials are "BA," as in "B A Baracus!"
I thought that emoticon sort of looks like B A Baracus.
DaveAtkins
RE: Frost depth for turndown slab
BA
RE: Frost depth for turndown slab
Dik
RE: Frost depth for turndown slab
Otherwise, I would start with ASCE 32-01 "Design and Construction of Frost Protected Shallow Foundations. Assuming you are in the US. The maps only cover the contiguous US plus Alaska.
RE: Frost depth for turndown slab
Hint.... Happy or not, you're in the wrong chat room here, given what you claim is your deficiency or lack of luck.
While you seem to know an awful lot about structures, buckling lengths and unbraced lengths, and the like. You've been looking for all the wrong things in all the wrong places, it's not unbraced your looking for, it's embraced. I'm sure there is a 25 or 30 year old chick out there who could show you a thing or two about the kl/r of you cantilever.
RE: Frost depth for turndown slab
BA