Can foundation be built around existing slab?

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Old 03-31-03, 05:41 PM
MostlyCranky's Avatar
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Can foundation be built around existing slab?

I am exploring options for an addition to my house that includes building a new garage, a new room, and attaching these structures to the house. The current garage is detached from the house and is on a slab.

I'm wondering about two things. One, can foundation walls be poured around an existing slab to form the base for part of the new garage structure? Two, can a slab be 'extended'? The current slab is 24x24 and the design calls for the new structure (24 x 30) to be located 8' further back from where it is today. That means 8' of the existing slab would be exposed and ultimately be paved over. I would then require a 14' extension to the slab to get the rest of the area. Would this extension be treated like new foundation construction with walls, and a poured floor?

Are these things possible, or is it less expensive to just have the current slab excavated first?
 
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Old 03-31-03, 06:11 PM
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YankeeCraftmn
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If you want a better job, definitely remove the old slab. I have never been able to reuse a slab in over 21 years, mostly because of grades, and a finished product look. Shouldn't cost that much to remove it. If you have a big enough lot you can bury it on it. Break it in small pieces though.
 
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Old 04-08-03, 04:50 PM
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Sorry, have more questions.

Regarding breaking up and removal of a slab. Any rough cost estimate per square foot in the New England?

The existing slab has been very stable over 17 years so it seems a shame to destroy it when an extension may give me what I need. You imply that it is possible to add another slab behind the existing one - I assume an expansion joint would be in order between the new and old slab. Could another 3 inches of new concrete be layed on top of the existing + new slab?

Finally, what about the foundation question? Is it possible to build foundation walls after a slab is already there?
 
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Old 04-08-03, 05:17 PM
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YankeeCraftmn
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Yse, you can put in a foundation wall if the slab is still there, as long as you do not disturb the soil under the existing slab.
No, you should not pour concrete over an existing slab, there is no way to bond them for strength and if there is a bad spot in the old slab you will find it in a hurry because of the existing weight of a new slab. Has the old slab been treated for termites, etc. usually you spray before you pour for these problems, here in N.C. we have too. There should be a concrete recycling place somewhere in you location, Here it is free, so all you have is the demo cost, a Bobcat will break up a slab in no time. Have a dump truck ready and the whole slab should fit in it. Here it would cost you roughly 1500-1800.00 to do.
Good luck.
 
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