Should One avoid using a monolithic slab in an Area where the Ground Freezes ?

[JRLF]

I live in Northern Nevada, where it gets very cold for four( 4) months of the year,viz. Dec- thru- March.

My home has a slab that was poured over perimeter footings that are 16 inches wide, and 30 inches tall, 24 inches below grade and 6" above grade,

with the footings reinforced top and bottom with two (2) # 4 bars, and with the slab reinforced with #3 rebar.

I recently asked a Contractor to work with a C.E. to come up with plans to add on an additional garage and heated workshop.

The plans he and the C.E. came up with have a monolithic slab, that is 12"wide at the perimeter, 4" thick, which is reinforced with 6x6x10 WWM,

and the perimeter of monolithic slab is reinforced with two #4 bars at the bottom, and one up at the top.

Being that my home is located in the most seismic area of Reno,that is, it's rated as Seismic Zone 3, but some at UNR have said it is more a "4" than

a "3', are any of you in agreement, from the little that I have read as an E.E.,that Monolithic Slabs should not be used where the ground freezes,

and wouldn't you also agree that 6x6x10 WWM is "garbage" compared to # 3 Rebar ?

As to the conditions of the soil here, whenever any excavation is done, all you come across is one boulder after another. That is, the soils present are

course granular soils and gravel that contain a considerable amount of oversized cobblers and boulders. Hence, the ground here is suitable for slab on grade

construction, and many builders in large developments here - use slab on grade foundations because they are a lot less expensive, but I haven't seen

any use monolithic slabs. In sum, what your opinion of using a monolithic slab, even with insulation on the perimeter, when the ground freezes ?

 

[CarlB]

Frost-protected shallow foundations FPSF) are a proven method for avoiding frost concerns. You could request the FPSF design calculations that would have been performed. Typically the thickened edge should extend to 12" minimum below outside finish grade, or maybe even 16". Insulation should be continuous from bottom of thickened edge to the wall above. Depending on climate (freezing degree days), horizontal insulation below grade may also be required.

 

[BigH]

The soil conditions you identify (coarse grained with boulders etc) suggests that the foundation material is non-frost susceptible. You didn't identify groundwater conditions. You might wish to check with your local building department, but with a non-frost susceptible soil beneath I would not be overly worried about effects of frozen ground.