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Old 07-25-2012, 04:44 PM   #1
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old house, no footings


I'm doing a home addition in the back of my house with a finished bedroom in the new basement. After the excavation I learned that there are no footings on the existing house. That messes with me a bit because it turns out that the top of the new slab is about even with the bottom of the old house.

I plan on pouring the slab such that it runs under the old foundation by 4" or 5" to give me a bit more of a connection, and I'm also going to pour it a bit high on the old house side (which works out well because my sump is on the opposite (downhill) side of the new addition anyway). I can't just pour the slab higher up because I'm already pretty much at my 7' ceiling height with the slab where it is.

I figure that I'll just try and make as much of a connection as I can between the old and the new (it's not very much, though, and makes me a bit nervous) and instead of trying to fight the water I'll just try and give it an easy path to the sump (via 6" of gravel under the slab).

How can I make the best connection between the old concrete and the new, and what other options do I have as far as keeping water out of my new basement?


Last edited by DIY1; 07-25-2012 at 04:49 PM.
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Old 07-25-2012, 05:02 PM   #2
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old house, no footings


There is no reason to connect the new foundation to the old foundation. You simply place the new foundation as an independent slab or slab plus footings. Connecting to the house has no structural importance. My basement addition is pretty typical, it was built immediately adjacent to the old basement, but has not structural connection, it simply butts up to it, and has a mastic type sealant to prevent water leakage between the two structures.

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Old 07-25-2012, 05:07 PM   #3
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old house, no footings


Quote:
Originally Posted by Daniel Holzman View Post
There is no reason to connect the new foundation to the old foundation. You simply place the new foundation as an independent slab or slab plus footings. Connecting to the house has no structural importance. My basement addition is pretty typical, it was built immediately adjacent to the old basement, but has not structural connection, it simply butts up to it, and has a mastic type sealant to prevent water leakage between the two structures.

My main concern is waterproofing, not structural. There is only going to be an inch or so of concrete (and mastic) keeping the water out at the seam between the old and the new. That just seems like a recipe for leaks eventually.

Like I said, though, I'm going to try to make it very easy for the water to head towards the sump underneath the slab instead of trying to get up and through that 1 inch barrier. I guess that's about all I can do.
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Old 07-29-2012, 02:47 AM   #4
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old house, no footings


Strong suggestion: Spend a few hundred dollars and get a qualitied structural engineers opinion.
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