Adding on to existing concrete pad

[Greg5OH]

I am putting a 12'x wide by 14' long shed up.
The picture shows dimensions and grade fall
Essentially the back end of the pad is about 2-3" below soil grade. I cannot go further back as there are massive tree roots there forming a wall.
I have exceptional drainage on the property.

My soil is very sandy with rocks and boulders everywhere. The pole barn beside the shop is a 32x32 single pour slab.
Foundation under the current existing 8x11.5 slab is just stone.

I have dug up and almost leveled the area, set up boards for the concrete form.

For the concrete:
1)Do I need to backfill with gravel, if none of the other structures or home which is slab on grade, use gravel underneath?

2)Should I isolate the new pad from the old via some 1/2" foam so the slabs move independently?

3) should the new add on pad be sectioned in 2, to not make it an L shape

4) do I need rebar for this concrete pour

5)Back of current pad is 2-3" below grade. The front of the new add on pad is 6 inches above grade. What should I do about the back? I plan on offsetting the shed 6" from the back and the left side of the pad.

Lots of questions, let me know your thoughts please and thank you.

 

[ConCretin]

1)Do I need to backfill with gravel, if none of the other structures or home which is slab on grade, use gravel underneath?

If the native soils after you have removed all topsoil and organic material are stable you can place concrete right on them. Its advisable to proof roll i.e. compact the sub base and then add a few inches of granular material to act as a capillary break and prevent ruts and mud if it rains.

2)Should I isolate the new pad from the old via some 1/2" foam so the slabs move independently?

This depends but smooth dowels and expansion foam allow some movement but keeps the slabs aligned vertically.

3) should the new add on pad be sectioned in 2, to not make it an L shape

If it’s L shaped, a couple control joints sectioning it into squares will (hopefully) eliminate the inevitable crack at the re-entrant corner.

4) do I need rebar for this concrete pour

I’d always go with steel reinforcing for an exterior pad because it’s subject to more movement than an interior slab. Rebar won’t prevent cracks or make the slab stronger but it will hold everything together if cracks occur. Properly supported wire mesh or #3 or #4 bars at 18” or 24” is plenty.

5)Back of current pad is 2-3" below grade. The front of the new add on pad is 6 inches above grade. What should I do about the back? I plan on offsetting the shed 6" from the back and the left side of the pad.

I’d add a concrete curb wall on top of the slab where it is below grade and thicken the slab haunch accordingly where it is above grade.

I hope that all makes sense. I didn’t see a sketch.