Is 80cm of gravel needed under a 25cm thick concrete slab for frost protection?

Hello,

my soil report states "The region is in frost impact zone I. Foundations must be protected against frost according to DIN 1054. For external foundations, a frost-free foundation depth of 0.8m must be maintained."

Now I have a quote from a civil engineer with an 80cm gravel layer under the 25cm thick slab. Our neighbor opposite built a similar house with only 20cm of gravel. Is an 80cm gravel layer necessary or can the slab be protected against frost in another way?

Best regards
Regina

Is an 80 cm gravel layer necessary

Yes. 80 cm is frost-free

…or can the base plate be protected against frost in another way?

Look:

in meinem Bodengutachten steht … ist eine frostfreie Gründungstiefe von 0,8m einzuhalten“.

Either frost skirt or gravel. I think gravel is the cheaper alternative.

The effect of frost is extreme. Many people cannot imagine these powerful forces.

While all materials contract when cold, water expands. This force cannot be measured. Anomaly of water.
Frost-resistant foundations are actually only possible from 1.20 m depending on the building area. 80 cm is too little. However, with a slab foundation, it is sufficient, it also depends on where you are building.

If you have layered or groundwater and it freezes at 50 cm, it will simply lift your house if the frost layer is too shallow.
Exaggeratedly speaking. Cracks in the house and damage to structural elements are the result.

In spring, when it gets warmer, the ground sinks, the house moves with it and then begins to shift. It acts like a small earthquake.

So I would definitely go for 80 cm, probably a bit deeper.

I believe in 1996 we had a very cold winter here in central Germany with continuous frost from November to early April. The ground was frozen between 1.20 m and 1.50 m deep. Greetings to the heat pump faction!

This resulted in massive damage, especially to water pipes, as many of these burst at a depth of 1.00 m. Also due to the expansion of the ground and the movements.

It always depends on the soil, the environment, etc. Sometimes 30 cm is enough, sometimes 120 m is too little.

It depends on where your concrete slab is located. If the top edge of the concrete slab is at ground level, then 60cm is sufficient. If the bottom edge of the concrete slab is at ground level, then at least 80cm of gravel should be used. If you build with a frost skirt, the gravel thickness is secondary (provided you don’t have high groundwater). The ground must only be stable. For example, if you have stable soil, a cleanliness layer should theoretically be enough, and then the frost skirt. Do you have a [soil survey]? It contains the foundation recommendation, which the [excavator] can also use for the offer.
We, for example, have a 1.00m frost skirt and on one meter 1.00m gravel and on the other side 0.20cm gravel. It depends on the soil.... the [excavator] then decides based on experience.

Do you have a soil survey?

That is how the post begins! The recommendation of the soil survey applies.

my soil survey states

Is an 80cm gravel layer necessary or can the base slab be protected against frost in other ways?

Frost skirts or frost screens are also possible. Each has its advantages and disadvantages. A thick gravel cushion is recommended, for example, if the soil near the surface is not particularly load-bearing. A frost screen (insulation extends over the base slab) can be implemented with little effort but has the disadvantage that water poorly infiltrates due to the insulation overlap. Generally, the soil expert will suggest the most suitable solution.