Garage foundation questions
I'm about to start on a 24x36 detached 2-story gambrel garage in southern NH. Planning on a standard 4' frost wall on footings.
1) Garage is to be built at the end of my driveway, which is fill from when the house was built 20 years ago. Front part of the footings will probably rest on original grade, but in the back it'll be on the filled area.
2) one back corner drops off so that at that corner I'll have to go down 10-12' to get to dirt, which will be pretty close to the original grade.
Looking for some opinions & education before I start talking to foundation contractors. My dad has bulldozer, backhoe & dump truck, so we'll be able to do the digging & filling ourselves, but figured I'd get a pro to do the concrete.
Building inspector didn't say anything in particular when I got my permit, so I don't think I'll be dealing with code issues so much as trying to make sure it holds up well.
I'm thinking that a slightly larger than normal footing with good reinforcing would be the critical part here - any suggestions for size?
On the corner with the deeper wall, what would be the normal way to handle this - drop the footing down, then build a wall to the height of the rest of the footing, then build the rest of the wall on that, or bring the low corner up in one shot with the rest of the footing?
Any comments welcome.
FYI, I'm not a foundation guy so I can't really offer too much help with your layout questions. I have done some work in NH before and I had to go down five feet on my footings, but if your inspector is fine with it, you should be allright. Have you done a soil test yet? In NH, I've heard of some unscupulous Mass. Contractors who used to take clean fill from sites they built on in NH and swap it out with urban fill from Mass projects. I suggest you check it out before you truck any fill out.
What the inspectors want is is the footing 12" below the frost line. They will have charts showing the depth which will achieve that in your area. Of course it may be cheaper to have a soil compaction test done on the backfill, see you've got the equipment to do it in house. If you don't have the room to work it with heavy equipment, then rent a elctric jack hammer with a tamping foot. The compaction test has to be down every 12" of fill.
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