Insulation under a low RC slab?

It appears this is on the exterior of the building?

If so, generally speaking that would be to prevent frost from affecting the building foundation more than protecting the slab itself. If your building foundation were frost-susceptible then this insulation could help prevent frost issues.

jayrod12 said:

It appears this is on the exterior of the building?

If so, generally speaking that would be to prevent frost from affecting the building foundation more than protecting the slab itself. If your building foundation were frost-susceptible then this insulation could help prevent frost issues.

Click to expand...

Yes, it's outside.

But how can it prevent frost issues? I mean, if the insulation does not reach beyond the foundation (about 1 m in the perimeter for example), then the ground below the insulation would still freeze and cause heaving - wouldn't it? Or do you mean that the insulation is elastic enough that the frost would compress the insulation a little when the soil below expands and the foundation would not move much?

Frost grows in a radial-ish pattern. So assuming the ground begins to freeze at the outside edge of the insulation, the theory is the frost wouldn't be able to penetrate all the way to the foundation. The thickness and length of the insulation is function of ambient temperatures and foundation depths. In your case, I'm skeptical of the amount of frost prevention provided by that detail. Since we know that the slab will be cleared all the time through the cold months, insulation only slows the penetration of the cold into the soils below. I do believe the intent is that some of the heat loss from the building will also help keep the frost at bay.

Do some research into frost-protected shallow foundations and that should turn up some stuff for you to chew on.