ᐅ Construction of a slab-on-grade with frost protection edging but without a traditional foundation

Hello everyone,

I would like to ask the experts for advice. So far, I haven’t found the optimal solution:

We are building a single-family house in 2013 with a footprint of 17 x 9 meters (56 x 30 feet).
The entire structure will be on a slab-on-grade with a thickness of 25 cm (10 inches), possibly increased to 30 cm (12 inches) — no basement!
I want to install a 60 mm (2.4 inches) thick Styrodur insulation layer under the slab.
My builder initially proposed strip footings 40 cm (16 inches) wide with insulation placed on the inside.
However, I want to embed the entire slab into this Styrodur insulation — essentially creating an insulated slab “box” without thermal bridges. A footing would create a thermal bridge where the slab meets the footing surface. The builder refuses to formwork the footing. Therefore, insulation on the footing side is not possible.
Now I am considering installing only a frost wall (frost skirt) with a width of 20 cm (8 inches) and a depth of 80 cm (32 inches). The slab should not be supported by this frost wall, which would run outside the slab’s perimeter.
I hope some experts understand what I mean and can share their opinions.

Thank you very much for your help.

Singerl schrieb:

The frost skirt would run along the outside of the foundation slab.

What else would it do?

Have you already discussed this topic with your structural engineer? They also have a say in it; before making a decision, a soil survey is necessary.

If, for example, you want to apply an external thermal insulation composite system (ETICS), gravel would probably be the better choice, because you can integrate it (also 80cm (31½ inches)) into the insulation.

Kind regards

I don’t have a structural engineer involved; I’m trying to save money. The construction companies in Bavaria usually work more by rule of thumb. But you convinced me. I’ll have a soil survey done. I believe the bending moments of the foundation slab shouldn’t be underestimated without strip footings.

I plan to build a 36.5cm (14.4 inch) wall using T10 blocks with two full stories. The price-performance ratio of these blocks is unbeatable.
I will plaster the exterior facade only in 2014 and maybe add external thermal insulation with wood fiber boards (if there’s still money left). That way, heating costs become negligible!

I appreciate any further opinions.

Regards, Singerl

That’s nonsense, Singerl.

There is no house construction without structural engineering. It is required for the building permit (planning permission). Your construction supervisor will therefore either have their own structural engineer or hire an external one.

Hello,

Singerl schrieb:
I don’t have a structural engineer, being cheap is cool. The building authorities in Bavaria usually go by rough estimation anyway.

Apart from the fact that you are not allowed to build without a structural engineer, you should not be surprised if in the end it turns out: "very cheap, very expensive!"

Kind regards

Bauexperte schrieb:
What else would it be?

I always thought frost skirts flush with the edge of the foundation slab???

Regards