ᐅ Is an 80 cm gravel layer necessary beneath a 25 cm thick concrete slab for frost protection?
Created on: 26 Nov 2023 14:50
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Regina1991
Hello,
My soil report states: "The area is located in frost exposure zone I. Foundations must be protected against frost according to DIN 1054. For external foundations, a frost-free foundation depth of 0.8 m (0.8 meters) must be maintained."
I have now received a quote from the civil engineer including an 80 cm (31.5 inches) gravel layer under the 25 cm (10 inches) thick concrete slab. Our neighbor across the street built a similar house with only 20 cm (8 inches) of gravel. Is an 80 cm (31.5 inches) gravel layer necessary, or can the slab be protected against frost in another way?
Good luck
Regina1991
My soil report states: "The area is located in frost exposure zone I. Foundations must be protected against frost according to DIN 1054. For external foundations, a frost-free foundation depth of 0.8 m (0.8 meters) must be maintained."
I have now received a quote from the civil engineer including an 80 cm (31.5 inches) gravel layer under the 25 cm (10 inches) thick concrete slab. Our neighbor across the street built a similar house with only 20 cm (8 inches) of gravel. Is an 80 cm (31.5 inches) gravel layer necessary, or can the slab be protected against frost in another way?
Good luck
Regina1991
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Regina199127 Nov 2023 19:23Thanks so far for the numerous responses. I am now in further discussions with the geotechnical engineer about the exact steps that need to be taken. If anyone is interested, I am happy to provide feedback on the final outcome.
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xMisterDx28 Nov 2023 18:43Regina1991 schrieb:
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Our neighbor across the street built a similar house with only 20cm (8 inches) of gravel. Is an 80cm (31 inches) gravel layer really necessary, or can the foundation slab be protected against frost in other ways?
(...)The ground can look completely different just 5m (16 feet) away, so relying on "But the neighbor did it like this..." when planning the foundation is not advisable... maybe the neighbor's work was just sloppy, or does your neighbor even know the results of their soil survey? My neighbors certainly don’t 😉
Oberhäslich schrieb:
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For example, we have a 1.00m (3 feet 3 inches) frost protective strip, with 1.00m (3 feet 3 inches) of gravel on one side and 0.20m (8 inches) of gravel on the other. It really depends on the soil conditions... the groundworks contractor decides that based on experience.Let’s just hope the groundworks contractor follows the recommendations from the geotechnical engineer and the structural engineer, rather than deciding based on experience alone...
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Oberhäslich28 Nov 2023 19:36xMisterDx schrieb:
You can only hope that the civil engineer sticks to the guidelines provided by the geologist and the structural engineer, and doesn’t decide based on experience alone...Our general contractor is very strict when it comes to materials and the bearing capacity test of the base slab. We had excellent results. On one side, there was a large clay-rich area, which was visible to the eye. That’s why I mentioned experience. This was also stated in the report with the different elevation levels. The civil engineer even excavated more soil than the report recommended. Although we gave away our soil for free and didn’t have to pay landfill fees, the final bill was around $20,000, twice the estimate based on the soil report. This just goes to show that groundwork can be a real surprise.
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