Should I Add a Second Story?
Q: "Is my concrete slab strong enough to support a second story?"
I'm toying with the idea of adding a second story to our detached garage. It was built 10 years ago, but I don't know if its concrete slab is strong enough. How can I find out?
—Jerri Gimlen, Waco, Tex
Tom Silva replies: If you still have the plans for your garage, turn them over to a structural engineer. He'll check them to find out how thick the slab is, how wide the footings are, whether or not the slab and footings were reinforced with steel, and what the compressive strength of the concrete is. With that information and a knowledge of local building code requirements, the engineer should be able to tell you if a second story can be added.
If you don't have plans, the engineer might be able to give you some useful information anyway based on photos of the garage exterior and interior, including the roof system, support posts, and any other visible structural elements. You'll have to pay for the engineer's review, but in my experience advice like that is well worth the cost.