How thick should a stone foundation be for a building without footing?

by Sherif Issa

Interesting, and not a very common question…. here are my 2-cents’ worth:

1. It all depends on the building you want to put on top of the stone foundation.

2. The stone foundation will be kept together using cement mortar or simply be compressed [consolidated] due to its own weight and the weight of the structure that will be added.

3. Doing a foundation from stone requires experience and a reliable source which could be hard to come by. I prefer you to use plain concrete instead.

4. The guides and software applications that help you design a stone foundation are few and far between, it will not be easy to design such a foundation confidently | safely, and economically at the same time. You will have to sacrifice one of the two parameters.

5. In all practicality, for a structure to be supported solely on a stone foundation – it must be a light structure, a maximum of a two-story wooden home. That’s perhaps why no one uses a stone foundation all by itself anymore.

6. For a larger, heavier building, you really have to go classic: use a regular reinforced concrete foundation system.

A standard isolated footing supported on a bed of stone foundation- image source: Research Gate

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However to answer your question, here are some points that may help you.

1. The minimum thickness of a reinforced concrete footing in most building codes is 30 to 35 CMs [12 to 14 inches]…. and as a rule of thumb, for each additional floor, you need 10 to 15 CM of thickness depending on the nature of the soil.

2. Therefore, for a residential building 4 stories high with normal live loads and normal sandy silt soil, your footing would be 40 to 50 CM thick.

3. So in case you are doing a stone foundation for a 1 story wooden home should be 60 CM thick, for two stories, make it 80 CM. The stones should be kept intact using a concrete mortar and well insulated from moisture.

4. These figures should be verified using manual calculations – or assisted by design software that specializes in foundations.

5. Finally, you should have a soil report available about the project site, as you may need soil replacement

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A typical stone foundation supports a light structure. Common in the US, Canada, and parts of Europe — But not around the middle east and North Africa

by Sherif Issa