how do you calculate how deep a building's foundations need to be?

Answer 1

If you don't know , then i suggest that you get someone to do the job that knows...what they are doing.

Answer 2

This is an open question, it depends on the soil and site conditions and the type of building, you can dig an inspection trench approximately 600mm deep x 600mm square then ask the local building inspector to give his advice, some land may not be suitable for just a trench and may need a full concrete slab.
The inspector may require you to dig it deeper and in another location.
You could also dig a trench down the side of your existing property and locate the footings, this will give you an idea as long as the site is level and well drained and there are no signs of subsidence or cracking to building corners or under ground floor windows.
The local building department is best as they will already know the area and local conditions, good luck.

Answer 3

If you are putting in a basement, you need a 12"H x 24" wide footing around the perimeter. The depth of a foundation is dependent on which latitude you intend to build. Out here on the great platte river road, we are required to have 42" for frost line conditions.

Basements can be depths from 8' to 10' ..

You should check with your location building inspector and ask him code requirements.

Answer 4

A building's foundations must be lower than the frost line (how deep it freezes in the winter). In places where it does not freeze (like San Diego) a foundation goes 12" below the finish grade. In Minnesota it must be 7' deep.

Answer 5

Well generally it depends on the buildings size, the condition of the soil, the type of foundations used, the strength of the concrete you'll use, the frost line in your area and other things. You'll need to have this designed for anything bigger than a shed.

Answer 6

You don't. Your architect guided by local building codes does. All soil conditions are different and some areas require pilings. Do you need a spread footing? Can you use block or poured concrete? How could these other answers be anywhere near correct when conditions and codes change town to town?

Answer 7

There is no fixed formulea. It depends on the substrate ( clay, sand etc )

If your working to building regulations then you'll need to get an archetect to tell you, a builder or planning dept will not tell you.

Architects are not expensive - ask a few builders and look for a "retired" one.

In the UK foundations now need to be good enough to take 2 storeys - even if you're builind just one storey.

Answer 8

If it's something you need to calculate, you shouldnt be doing it. You should be getting an engineer or an architect.
If it is something defined in local building codes then you can probably get copies online or from your local municipality and go from there.

Answer 9

All 3 of the first answers are valid. It isn't something for you personally to calculate however,,,unless you're an engineer/architect/contractor and know the local zoning and code laws.

Rev. Steven