Expert: Dan Griffin - 10/23/2009

Question
I have a concrete slab in that we would like to build a room addition on. What is the best way to verify that there is a footer present? (there is no place to dig down along side, a concrete patio butts up to porch)

Answer
Mark, can you not dig at one end or the other?

This will NOT satisfy a good inspector, but will tell you whether you can expect to find something.  Get a good SDS hammer drill with a 24" long drill bit.  I would use about a 1/2" bit.  Drill a series of holes in the porch to note how thick it is and as you approach the exterior, see if it is thicker.  The holes can be easily patched (yes, they will show if you don't ever have a finish floor).  In order to truly determine whether the footing is large enough and deep enough to satisfy the requirements may well force breaking a diggable (is this a word?) hole.  Assuming your addition will have carpet or other flooring, it is easy to patch and cover.

I can't think of any other approaches.