I currently have an existing screened-in porch resting on a concrete slab. I have dug around the slab in 4 random places. What I have determined is that the slab was actually poured 2 different times, both times using 6"dimensional boards, thus roughly giving me a 10" deep slab on which the current porch sits.
I now would like to build an addition onto my house where the porch stands. I was wondering if I could dig 36" down for footers(I live in Pittsburgh) around the slab, then pour concrete for the foundation around the concrete slab currently in place. I would like to keep the current slab in place for the base floor.
I suppose I will need to pour the foundation instead of using block. What width of pour will I need?
In addition there is a 6" stepdown from the house to the slab. Could I raise the floor by putting down a treated wood frame? This way I can level,vaporbarrier treat and insulate below the subflooring.
As with all questions I would like to go into building inspectors office with some type of plan in my hand, not looking like the town dummy!