Frost apron - advantages and disadvantages

Sure? Best regards

Sure, why else? Strip foundations are for load transfer of the walls in single-family houses and for frost-free foundation without a basement. In our case, despite having a basement, a strip foundation was built because the soil consists of clay and sand.

I will copy the description as it is in my contract. I also have a floor slab with frost protection skirt, on normal ground.

For improved thermal insulation, an approximately 8 cm thick vertical insulation is installed around, up to a depth of about 40-60 cm, between the soil and the foundation concrete as a frost and thermal protection skirt. With this construction, we already demonstrate our competence in energy saving in the foundation phase.

I am not a civil engineer by any means and am happy to be corrected, but a frost skirt is not a strip foundation. The former is meant to keep water away, the latter to transfer loads. They look similar in construction because concrete is poured into a trench, but they have nothing else in common.

Of course, you can build on strip foundations (and lay them at frost-free depth), but then the slab is dimensioned differently and no longer serves as the (sole) load-bearing element, otherwise it would unnecessarily cost more.

If the slab itself is used for load-bearing, you do not need a strip foundation, but you must somehow prevent the slab from being lifted by freezing water. This can be achieved with a surrounding, waterproof concrete wall, i.e., a frost skirt.

But just as well by replacing the subsoil with non-frost-susceptible material (e.g., foam glass gravel or the like).

The insulation of the (strip) foundation, or the edge of the slab, in turn, is intended to prevent thermal bridges at these points, but it certainly will not keep frost away. Strictly speaking, insulating these areas in this context is even counterproductive because it withholds the heat of the house from the soil there.

Frost skirts are usually omitted in construction with a load-bearing slab to ensure continuous thermal insulation. They are functionally unnecessary on non-frost-susceptible soils. They can also be made cost-effectively using gravel where this is not naturally given. It has nothing to do with stinginess. The necessity is evidenced by a soil survey. Many roads lead to Rome.

That is not entirely correct. The "teaching" always calls for a frost skirt in the case of floor slabs. It is a more recent phenomenon to argue that if the ground beneath the foundation is frost-proof, frost protection has been demonstrated. See if you can find a building without a frost skirt for a public client; due to pre-programmed legal disputes, probably not.

Hello, as already mentioned, the necessity of a frost skirt arises from the soil report. With our general contractor, a load-bearing ground slab with a thickness of 25 cm frost-free foundation was the standard; due to the soil conditions (summer frost), an additional continuous unreinforced frost skirt had to be installed.