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Old 12-27-2011, 06:42 AM   #1
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Extension foundations

I am planning to build a single storey extension to my home next year. There is an existing concrete slab in the place where this extension is going. It is 5 inches thick high strength well matured concrete. I am reluctant to go digging this concrete up to make a foundation for the extension. It is structurally viable and safe to buid on the existing slab or can I in some way put extra concrete overground to hold up the new building or is there some kind of overground lintel available?



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Old 12-27-2011, 08:39 AM   #2
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Simply put, the addition foundation has to be of the same type of construction as the existing house foundation. If the house is sitting on a simple slab-on-grade, you "may" be able to use it, but not likely.


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Old 12-27-2011, 08:53 AM   #3
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You need to discuss this with the building inspector. I assume you are planning to get a permit, and the local building code will undoubtedly have a section on allowable foundation types. In my jurisdiction, an extension on a slab would be totally unacceptable, foundation needs to be below frost, which is 4 feet in my area. However, you did not state where you live, so perhaps you do not live in an area subject to frost, and possibly you do not need a permit, so a little more information would be useful.
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Old 12-27-2011, 09:08 AM   #4
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This is an example of why it helps to have your location in your profile. What Daniel would do in Boston is not the same that would be done in California.

I am in the middle of a 2-story addition to my house. Exisiting house is raised foundation (crawl space). The addition is half slab and half crawl space. It was all pretty complicated....

Your soil conditions are going to be a big factor....as much as I am a DIY'r....this is one area where you need to hire an expert.....it's ok to do the work yourself....you just want to make sure your doing it the right way. That answer will not come from a DIY site.

If you want an example of how extensive my foundation is, have a look at the addition link in my signature.
Even if you are on the right track, you will still get run over if you just sit there.

My 2-Story Addition Build in Progress Link ... My Garage Build Link and My Jeep Build Link
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