Concrete Foundation Depth?

Old 02-23-10, 02:24 PM
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Concrete Foundation Depth?

Hi All,

Long time listener, first time caller.

I am building a 10x12 shed in Northern California (no frost/snow). I would like to pour a concrete footing for 2x6 framed walls. I'd like a slab floor in between the footings. What I don't know is how deep the foundation/footing must be. The soil is beautiful top soil for about 2 feet and then sticky clay the rest of the way.

Thanks for the education.

Old 02-23-10, 05:49 PM
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Originally Posted by gmonhog
...Northern California... (no frost/snow)....The soil is beautiful top soil for about 2 feet

someones jealous

Don't worry someone will be along to actually help you!

I do believe however that a substrate of sharp edged aggregate (crushed rock) will contribute to overall stability so you don't have to use so much concrete.

Any way, like I said...
Old 02-23-10, 06:34 PM
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"Beautiful top soil" does not make for a good base to put a structure on.

You need something that is granular and can be compacted to hold up in spite of any moisture that happens to occur.

Bring our stem walls about 8" above your finished slab and pour a 4" slab between the stem wall projections. This will make everything cleaner and easier to maintain. - It also gets your wood above the finished exterior grade.

Old 02-24-10, 04:53 AM
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Here in NC any time you do a footer, slab or foundation it becomes a permanent structure and the building codes dictate what is required. If it is built as a temporary structure (no permanent foundation, no concrete floor) then no codes apply and you can do whatever you want.
Old 02-24-10, 05:48 AM
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Hi gmonhog, Pilot's point is a good one. I get the call anytime a friend wants to build a shed, so have done more than I can remember. However, I always recommend against a concrete floor. Moisture from the ground up or from condensation from humidity always creates a problem. A wood deck set off the ground can allow ventilation underneath and thus remain dry in all weather. Plus, if you change your mind on location, I have moved similar size sheds by myself. The last one I advised on liked the idea that when their need was fulfilled, they could sell it. In some areas around me, less than 100 sq ft avoids the tax man. Certainly avoiding the code requirements could be an issue.

If you need other suggestions on the shed, I've seen a lot of advice on the forum, as many have been there.

Old 02-24-10, 06:41 AM
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At over 10x12 (120sf), this could require a permit in many areas. Some areas have a cut-off at 96 sf or 120 sf.

If you are in an uncontrolled area, you can do what you want and your neighbors can do the same. If this is the case, just make sure you have proper foundation if you decide to go the cheap and flexible way and be able to move it. Just have sure the wood is far enough from the finished grade.

I am aware the some areas of northern California can have a lot of moisture that should be a consideration.

My son had a maximum of 120 sf to eliminate inspections, so he built a 10x12 shed on a concrete slab with a raided curb, but he made it 10' high at the sidewalls and got a lot better access to everything since hanging and above the ceiling joist storage made a world of difference.

Just make sure you have the legal set-backs since the zoning has nothing to do with codes.


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