- Joined
- Mar 13, 2005
- Location
- Raleigh, NC
does having the center 4" save that much concrete ?
It reduces the volume by 1/3 over a continuous 6" slab.
So long as the subgrade is properly prepared, 4" is plenty. Especially so if you add a little WWF for reinforcement.
I would thicken the edges, though. A turned-down edge for a footing should be at least 12" deep by code, more if you're in the mountains, and at least 12" wide. Less will probably be fine, unless you're looking to put an apartment upstairs or something like that.