I am thinking of building a garage on an existing parking area of our driveway. Is it kosher to use like the back corner of the driveway to build a garage? I am thinking something like with a 3’ tall block wall then 8’ on top of that for an 11’ inside hieght. I doubt this is a monolithic slab area prolly gonna be just 4” thick everywhere. Wasn’t around for the house building. 24’ x 24’ approximate size. Advice and guidance requested and appreciated

You need a footing under a load bearing wall

X 2

So would need to cut out the pad at the perimeter of building and dig out and pour 12” wide by 18” deep of concrete ? Might be better just to leave pad asis and put in a proper concrete floor to the side of it. The driveway pad isn’t pool troweled like a proper garage floor.

18” deep would be a little excessive but on the other hand you’ll probably have to pay a short charge for concrete so might as well pour it thick and a little wider.

Also make sure you know how the water will drain around it. Dealing with a water problem now where the previous owner built a storage room on a pre existing slab.

This.

This^^^ times ten.

It's really not that hard to run a quick calculation of the contributory area (Roof dead load + Snow load) x S.F. then add the weight of the C.M.U. walls to that and actually see what your loads are going to be. Then, once you know that you can size the perimeter foundations accordingly. This includes factoring in the bearing capacity of the soil in your particular area. There are numerous charts online for find out what the bearing capacity of your soil is per S.F.

You're going to spend a considerable amount of time and money and effort building this thing, so that last thing you want is for it to start sinking and get huge cracks in the concrete driveway. Speaking of the drive way... My guess is that it may not be a reinforced slab. Which is not good either.

All that math... And yet there's 200 year old barns, still sitting on rock piles, all over the country. 😉

True. But they're not level. And they're not built on a driveway slab.

Agreed again. Just make sure you put the footings on good native soil or properly compacted fill if any part of existing slab is on fill. Attention to good building practices on a retrofit where you are introducing new loads will serve you well in the long run.

Good point. There are 80 year old houses on cut cedar stumps all over Walker County too. Most of them have character swags now and the interior floors have more undulations than the greens at Augusta

In Alabama, you need the top of the footing to be 12" below the finished grade. Like straycat and others said, do not build it on the driveway. Driveways are often placed on fill material excavated from the house foundation and your garage needs to be on firm native soil or compacted fill. Inspectors sometimes carry a water meter key which has been sharpened to a point on the end to check foundation excavations.

I wouldn't advocate constructing on rock piles. But I'm always amused by the amount of formulating to dig a ditch with a backhoe. 😆
Reminds me of military protocol; measure it with a micrometer, mark it with a chalk stick and cut it with an ax!