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Old 02-16-2013, 07:34 PM   #1
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Digging out a basement...?

I’m looking into finishing my basement and one of the issues that needed to be corrected first is the seepage issue. I’m in the Chicago area, so these are common issues around here (both seepage and height of basement). Our home is almost*100 years old*and we get waters seeping in at the*cove*joint. When getting a quote for drain*tile*and a*bathroom*rough-in, a contractor suggested tearing out the entire basement*floor. It has areas that are uneven and cracks and such, but I was going to get some self-leveler to handle that. He mentioned that in doing so he could probably get us an extra 6 inches or so of headroom. Right now, headroom is a big issue for us- but since we were just*planning*a rec room down there, we weren’t overly concerned. Although 6 inches isn’t a lot, it would make the area much more comfortable. He said that they would be tearing out the entire perimeter and portions of the floor for the bathroom, so he said now would be the time to do this. The additional cost is only about $5k, if I combine it with the*drain tile*and bathroom rough-in job. Since it’s not a huge difference, he said that he would leave the*water heater*and*furnace*as they are and there would just be a little stoop that they are on. This doesn’t matter much to me because we are going to box in it when we finish it anyways.

*My concern is whether this would compromise the structural support of the house…

Any thoughts on this? Would the foundation need to be underpinned, or might it be fine since were talking six inches?


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Old 02-16-2013, 08:23 PM   #2
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You may not dig below the level of the bottoms of the foundation footings without following special rules, otherwise the footings and walls can slide out from under the house.

With this restricion in mind you will probably not be able to gain 6 inches of headroom with just straightforward excavation and also be able to install perimeter drain pipes.

Method 1. Undisturbed earth must slope down from the bottom edge of the footing no steeper than 20 degrees, or about 3 inches of horizontal run for every one inch down. For 6 inches down the new perimeter of the basement floor will be 18 inches in from the footings which of course reduces the floor area.

Method 2. Dig as deep as you want but don't expose more than two feet worth of footing horizontally. Build a new footing and foundation extension under the existing footing to shore it up. Now move on to the next two feet. Some engineering is needed to figure out the needed thickness of the wall extension going down to the new footing. (You can work on four 2' places, one on each side wall, simultaneously; professionals have equipment and ways to work on longer stretches.)


The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

Last edited by AllanJ; 02-17-2013 at 08:00 AM.
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