Adding a basement next to existing house.

[POC]

What is a Michigan Basement? | Prugar Consulting, Inc.

My grandparent's house had a basement like this. There was a concrete shelf about 2-3 feet wide that went from the top of the actual basement block wall to the bottom of the original crawlspace foundation. The basement wall is set inside the original house perimeter.

Perhaps you could do something like that on the wall where the addition meets the existing house, and a regular poured or laid block wall for the other three addition basement walls.

Tying the two parts of the house together would depend on which direction the new floor joists run, parallel or perpendicular to the existing house floor. Parallel sounds easier. I assume your goal is same height floors in both parts.

This is the way I was planning on doing it.

 

[dave1949]

This is the way I was planning on doing it.

That way would be the least messing with the original crawlspace foundation or disturbing the house framing. The trick is to do it well--as usual.

If you put a footer and wall for the addition out about 3' from the existing crawlspace wall, make the new wall even with the top of the existing crawlspace footer, back-fill and compact the 3' gap, then cap that 3' gap with 3" of concrete that rests on the top of the new wall over to the top of the existing footer maybe.

If needed for regular joist support, you could put short adjustable floor jack posts on top of the new wall before pouring the concrete cap. Being height adjustable it will help with getting the new and old floors at the same height.

If you have decent drainage now and put good drainage around the new basement, I don't think hydrostatic pressure on the "Michigan" wall would be an issue since it will be under the center of the combined old and new sections and not exposed to much exterior water runoff. A Tee buttress/deadman in the middle of the "Michigan" wall would add some insurance against that wall being pushed by soil pressure.

If you don't have good drainage or a wet site in general it may not be the best method. My grandparent's basement never had moisture or support issues and looked a lot nicer than the pic in the link I posted. But they were on a dry site in a city with storm/sewer drains also.

 

[Cord]

So, I have a 24x36 Cape Cod style house on a 4 block crawl space. I want to add an addition at one end of the house with a basement. Has anyone done anything like this? How would I go about doing it? I've read that you can't dig right next to the existing foundation due to the compression "plume"(?) being wider than the actual foundation.

So, what say you TBN? Can it be done?

Couple of ways to accomplish this. If you don't mind losing some basement space, the easier, cheaper method is to build a knee wall in front of the existing footing so you won't have to disturb the existing foundation. If you want to maximize the space, then you will need to underpin the existing footing. Two options: you can either pour the wall in segments or temporarily support the house and then demo the existing wall and footing and pour it back.

 

[SPIKER]

one other option may be to dig a basement that will fit the new addition AND the existing home then move the existing home onto the new build and new basement.

otherwise I would jack up existing house support system with some beams so you can make it attache directly to new build/addition. I have dug out basements under existing houses not easy or quick by hand or by small equipment.

Mark