X-posted in a outdoor board

We have a detached garage that I want to replace with a bigger metal building. (PEMB type). a structural engineer I consulted said the foundation is still in good shape. It's a typical 20x20ish detached garage and I would like to put at least a 35x35 metal building. I would like to hire someone to add to the slab. Is 12" footers good enough in Houston ? Not going to put a car lift or anything. Should I hire an engineer to design the slab addition ?

Yes engineer

jt2hunt said:

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Yes engineer

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You will need an engineer. You want to match the existing slab, including subgrade, as much as possible so that any movement the two experience will be the same. This may not be possible with a 15' x 35' addition to the edges of an existing slab. Especially in Houston.

If you're in city limits, check your building codes to make sure there are no limitations on sf or materials. I was looking at building a 40x40, and I was l in limited to 40x33 because of lot size restrictions.

IF your SE = "a structural engineer I consulted" cannot do this, perhaps he can oversee an Architect or other to draw a solution.

IMHO

• Perimeter beams: 12"d never worked in Aggieland, nor even 24"d in many places the reasons would be TMI here
• A slab with a hole in it (the existing slab) is one of the most unstable design problem to solve on unstable supporting soils

Otherwise, good idea, so long as pros are your guides, as all mentoned above

AW 1880 said:

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If you're in city limits, check your building codes to make sure there are no limitations on sf or materials. I was looking at building a 40x40, and I was l in limited to 40x33 because of lot size restrictions.

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Are you in Houston?

I can't see any reputable engineer signing off on something like this. And I don't see the COH approving it either but maybe I am wrong.

I've seen a recent project where perimeter grade beams were added and then a full 4" slab placed on top of the existing without removing the old.