Combination of concrete wall foundation and slab on grade.

[woodman1967]

I have a client (single family residential) who is asking for a foundation that is a standard ICF 8' wall supporting about 1/3 of the house footprint (they want utilities/mechanicals and storage here). the ret of the house they want slab on grade (they want the floor finish to be polished concrete). Of course they want the finish floor to be flush where the two foundations meet.

I try to avoid mixing below frost foundations with above frost foundations. Also, to get the floor joists and finish floor of the standard basement to be flush with the polished slab will be a bear to accomplish IMHO.

I would like them to have a frost wall foundation in the area of the desired slab, have the same floor joist system throughout. If they wanted the concrete flooring they could add concrete topping on the floor system (using proper dead load of course)

Is this an issue (combining the types of foundation) or am I making a mountain out of molehill?

The house is located in eastern Canada so freeze/thaw is a major concern. The frost line here is 4' as well.

 

[jayrod12]

I agree with your concerns. There will inevitably be differential movement seasonally between the slab-on-grade and the structural slab areas.

I'd be putting the entire thing structural.

 

[woodman1967]

Thanks Jayrod,

There is a bit more info to this...the client wants to now go with a frost protected shallow foundation. But this house is to be built into the slope of the lot. Basically it's a walkout basement without the "rest" of the house. My concern is that this will be essentially the same problem, the back of the house built below the frost line, the front at the frost line. Would it be better to go with a frost wall around the area at frost level? Like a standard walk out basement?

 

[jayrod12]

Yeah, horizontal rigid insulation to prevent frost penetration would possibly be a solution.