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DIYer
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Discussion Starter #1 (Edited)
Thickened edge slab foundation (monolithic pour) - seeking thoughts on dig vs no dig

Hi all, I am of the DIY sort and not pro so please forgive any ignorance on the topic

I am looking to form a 20x40' slab for a shop. Its been approved by the county for thickened edge with footings 12" tall and 12" wide. The ground does not freeze here so do not need to go down to a frost line. I will take a box scraper and remove all top soil/organic matter.

My thought is that I will either bring in rock and form solely with that (no digging) or I will rent an excavator and dig a shallow trench for the footing and then bring in rock for the remainder (I would dig by hand but the ground is incredibly hard)

Your thoughts would be appreciated.
 

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Residential Designer
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Generally speaking, you would excavate so that the bottom of the footing is 12" below the surrounding grade. Then the top of the slab would be 8" above the surrounding grade. The grade is then sloped away from the structure for a minimum of 2% grade for 5'.

Obviously you do not have a set of approved plans for this structure and being that all counties/cities in California are required to build per CBC or CRC I don't understand the statement that it is approved for what is obviously a slab-on-grade foundation. If you don't have plans how do you get approval?

Is this on reservation land? That is the only land in California besides military property that one does not need plans and permits for.

Andy.
 

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So how's that going to work out for you when the organic matter you left in place rots and sinks?
 

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DIYer
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Discussion Starter #4 (Edited)
Generally speaking, you would excavate so that the bottom of the footing is 12" below the surrounding grade. Then the top of the slab would be 8" above the surrounding grade. The grade is then sloped away from the structure for a minimum of 2% grade for 5'.

Obviously you do not have a set of approved plans for this structure and being that all counties/cities in California are required to build per CBC or CRC I don't understand the statement that it is approved for what is obviously a slab-on-grade foundation. If you don't have plans how do you get approval?

Is this on reservation land? That is the only land in California besides military property that one does not need plans and permits for.

Andy.
This is for a metal prefab building on ag land and standard set of plans from the company were submitted and approved. Attached is the foundation detail

As drawn it has the footing 12" below grade "or as required by local building code" (as far as Im aware, there is not a 12" requirement to be below grade but I could be wrong, wouldn't be the first time)

If there is a 12" below grade requirement, could I not scrape away some number of inches, pour the foundation, then backfill the edges to create the necessary slope away?
 

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Residential Designer
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1,483 Posts
This is for a metal prefab building on ag land and standard set of plans from the company were submitted and approved. Attached is the foundation detail

As drawn it has the footing 12" below grade "or as required by local building code" (as far as Im aware, there is not a 12" requirement to be below grade but I could be wrong, wouldn't be the first time)

If there is a 12" below grade requirement, could I not scrape away some number of inches, pour the foundation, then backfill the edges to create the necessary slope away?

Ah, so you do have approved plans then. The plan checker was not doing his job then as he should have had you show that the min. distance from the sill to earth is 8". That is code in CA. now.

As for the rest of it, I do not understand what it is that you are proposing to do with scraping away some inches? Then pouring foundation? Then back-filling?

I don't get that.

Andy.
 

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Civil Engineer
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I believe the OPS is asking if he can scrape away four inches, place a 12 inch high footing, then backfill the footing with 8 inches of soil. This would put the bottom of the footing twelve inches below finished grade, but only four inches below original grade. At least I think that is the question.

A question such as that could be answered by the local building inspector. Of then the code on foundations has more detail than simply how deep, there can be requirements for strength of soil, removal of fill material, removal of organics and topsoil etc., but your building inspector will understand all the local requirements.
 
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