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I am purchasing a small one-story home built in 1955. I want to turn the garage into living space. The home sits on a crawlspace, but the garage is on a slab that was added to the side and abuts the original home. The garage is attached and looks like it was originally built for the house -- but it wasn't. It was added on later.

I want to convert the garage space into living space but am concerned that because the garage slab foundation was poured only for the purpose of a garage that it's not suitable for being remodeled to living space.

How can I tell whether the foundation of the garage is suitable to build on?

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    What exactly do you want to build? One story? Two-stories? – GdD Oct 18 '12 at 7:42
  • Are you concerned about the slab, which is the large field of concrete that fills the floor of the garage area, or the footings, which would be underneath the slab around it's edges and beneath any key stress points? – The Evil Greebo Oct 18 '12 at 9:32
  • Have you contacted your local permit office? Chances are, they'll require an engineer to inspect the site before issuing a permit. The engineer will tell you whether or not the slab is adequate. – Tester101 Oct 18 '12 at 16:47
  • Are you planning on a simple conversion (installing flooring, closing off garage door, etc.), or are you planning to build a second story on top of the garage? – Tester101 Oct 18 '12 at 16:48
  • Just a simple conversion. No second story. Install floor, a few non-load-bearing walls, drywall and some carpet. Then running electricity, heating and putting in two windows. – Trevor Oct 19 '12 at 5:26
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The first step is to look at the foundation that supports that the walls of the garage. If the walls have foundations separate from the garage floor slab and those foundations are similar in construction and depth to those of the main house then this is a good indicator that you are in a good position to proceed with the remodel plans.

On the other hand if the slab was poured with integral footings around its periphery that are similar in size and depth to those of the house then you are also probably good to go forward.

If the garage is simply a thin floating slab then a whole lot will depend upon the climate in your area, the type of soil, the lay of the land and local code requirements. You may be in a good position if the "attached" structure of the garage to the house is sound, the slab shows no signs of cracking and shifting and the construction technique is up to code.

In any case it may be well to check with the local permitting authorities and/or bring in a consulting local contractor to give you ideas and make suggestions.

One last thing that comes to my mind regarding this potential project is the evaluation of whether the garage slab is below the floor level of the original house or not. If it is below you may very well want to consider the possibility to build up the floor to the level of the house. This will help to make the added living space feel like proper part of the house and make movement into and out of the space a whole lot more natural.

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    Also, raising the floor gives you an insulation opportunity that will make it much easier to control temperature than if you use the concrete as the subfloor. – bib Oct 18 '12 at 13:00
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    +1 for the floor level remark. My bedroom and bathroom are in an addition that's a half-step below the rest of the house and I fantasize daily about raising the floor. – ArgentoSapiens Oct 18 '12 at 13:01
  • It's just a slab next to the main foundation of the house. The back, side and the end front walls are on the new slab foundation. The wall that's shared with the house was once the outside of the home. – Trevor Oct 18 '12 at 16:21

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