For small residential buildings that are ground level or at least 1 1/2 times the width of footing, the minimum depth is around 5 feet. In colder climates, the depth of foundations is a minimum of 1 1/2 meters below the surface due to frost.

How thick should a concrete base be?

As a rule of thumb, concrete slabs supporting lighter weights such as paths, patios and shed bases will need to be 75-100mm thick, while driveways and garages need to be at least 100mm thick. Slabs intended for commercial use should be at least 175mm thick and reinforced.

How thick does a concrete base need to be for a shed?

A 4-inch slab is generally a good thickness for a typical shed. This concrete floor can be poured in most locales on a 4-inch base of compacted gravel. That requires an excavation of at least 6 inches to make a slab that will be 2 inches above the surrounding ground.