question on footers and foundations

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If you are digging the footer for a 18 by 20' slab ,13-14 inch wide footer ,how far apart should the rebar be on the 12inch cradles/supports?..is it ok to go with what i have(12 inch wide supports )vs the smaller cradles -7 or 8?
there will be a 12 by 12 inch/ footer with 4-5 inch high slab.

I also wanted to know if the correct order i plan to lay is ideal before pouring
concrete-on packed dirt:3inches gravel--then 4ply sheeting,then the concrete..(some have said sheeting --then gravel)..
Any info is appreciated.

Willie T

The main thing you need to be concerned with is keeping the rebar at least 2" away from all the edges of the footer.

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Willie T

jomama45

What Willie said about the rebar & the plastic goes directly under the concrete, over the gravel. Just use some caution not to destroy the poly when pouring. This is generally why 6 mil poly is used under concrete.

Aggie67

I hate to ask this because I think I know the answer, but what did the design call for?

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vsheetz

Gravel, not sand?

Termite

Me too. You need to check code in your area if you don't have a design. You can check it in the code book, but you'd be better served by checking with the local inspector.

Termite

I can't say its that way everywhere, but around here you do not put sand under a slab. Gravel is the standard. In the thousands of slabs I've inspected in my career I've never seen sand under one of them.

hidden 1

I spoke with inspector and yes it is gravel-1-3 inches then plastic(for my area).and the rebar is to be about 3 inches in from wall of footer,paired.
Will a bit of gravel, atop plastic also ,aid in anything?
Is it best to pack down the dirt first before packing gravel?
I also have a pretty sandy area and plan to remove it and place clay soil over it also for a more solid foundation.
Any info is appreciated

hidden 1

I also was wanting to know how deep into the footer to run the conduit for the electric to the detatched garage.I will be linking it to the patio junction box and not using those lights any longer after completing it,kind of like swithing the lights to another location(its about 10 ft away). Do you have to use a new panel box ? What are requirements?