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Addition with deeper full basement added to existing full basement?

Addition with deeper full basement added to existing full basement?

Old 12-06-14, 07:37 AM
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Addition with deeper full basement added to existing full basement?

I am contemplating adding two bedrooms, a bathroom, and a laundry room to the rear of my ranch (making it an "L-shaped ranch," basically)-the footprint of this would be 20' deep by 25' wide. My current basement is not a walkout, but about 8' out from the existing foundation wall, the grade slopes pretty well, so at the end of the new addition it will be easy to add a walkout door with small retaining walls on either side if need be. Since we already have an attached one car garage and a large finished basement family room as well as some unfinished storage/utility space in the existing basement, I'd like to use the new 500 SF basement as a storage shed/shop. I plan to use it to store/work on power equipment, store firewood, and serve as a backyard shed.

The foundation will be a pretty straightforward box added onto the back of the house, nothing too difficult there, however, the height of the existing basement (surface of slab to bottom of floor joists) is about 7'-3. I'd really like the height of the new basement to be 8' or slightly more. Doing this while keeping the height of the main level the same would of course require digging the new foundation deeper than the existing foundation. Is this something that is typically done or is the risk of undermining the existing foundation too great? We're only talking about 9" or so, but that's enough to get underneath of the existing footings.
Old 12-06-14, 08:48 AM
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There shouldn't be a problem but either way, you need an architect to draw plans. He will know for sure.
Old 12-06-14, 09:29 AM
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You definitely want to tie the foundations together with rebar.


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