by Sherif Issa
Interesting, and not a very common question…. here are my 2-cents’ worth:
It all depends on the building you want to put on top of the stone foundation.
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.
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.
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.
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.
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
However to answer your question, here are some points that may help you.
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.
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.
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.
These figures should be verified using manual calculations – or assisted by design software that specializes in foundations.
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