# concrete slab thickness--southern Cal



## HighDesertHomeOwner (Nov 24, 2010)

My house has a typical southern cal slab floor.

The slab  is mostly about 8 inches thick. 

But the slab for the garage is only about 3.5-4 inches thick, except at the perimeter which appears to be the same thickness as the rest of the house.

I plan to build an addition of about 270 sq feet, extending about 12 feet from the double slide door into the yard, about 22 feet across. It will be framed and enclosed as a recreation type room addition.

The question is whether the whole 270 square feet of the slab must be of the same thickness of the house, ie about 8 inches thick? Can I duplicate the same as the garage? That is, have the perimeter about 8 inches thick and the inside sunken area only about 3.5-4 inches thick.

Thanks


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## paul52446m (Nov 24, 2010)

HighDesertHomeOwner said:


> My house has a typical southern cal slab floor.
> 
> The slab  is mostly about 8 inches thick.
> 
> ...


 I don't know anything about your building codes out there,
 but are you sure the house is all 8" or just 8" around the edge?  A 4" slab is fine for a house. You might wan't to check you building codes there. In a lot of areas i think the outer footer has to go down 16 to 18" so animals don't dig under your slab. paul


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## HighDesertHomeOwner (Nov 24, 2010)

"I don't know anything about your building codes out there,
but are you sure the house is all 8" or just 8" around the edge?"

There is no sunken part of my house except the garage.

Clearly, the slab except at the garage is about 8 inches above the ground. If the slab for most of my house is only 4 inches thick, then there must be piled up earth (dirt) except at the perimeter. 

 I have to step down about 4 inches going into the garage from the rest of the house.


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## GBR (Nov 25, 2010)

Check with your local B.D. as you live in a seismic area as I do. This will require thickened perimeter footings not only to carry the walls and roof, but also tie the special steel hold-downs to the earth. Work with the B.D. and create a paper trail for your H.O.Insurance (to pay any claims) and proof of built to minimum safety Code when selling the house (as well as additional square footage). 

Gary


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