Garage under - crazy idea?

mjlbJuly 9, 2012

This a hypothetical question, as I am not going to buy the house that prompted my inquiry. But now my curiosity has the better of me, and I hope that an architect or builder or engineer will comment.

A rough sketch of the property looks like this:

The two-story house (with full basement under) is about 45' x 30'. The basement has support poles in the center about 8-ft apart. The one-story part (with garage under) is about 12' x 18'.

The logical places to add a second garage space would require variances, as they would place the garage too close to property line setbacks. So I entertained the idea of converting about half of the unfinished basement to parking. A big opening into the house foundation would be required... yikes! And I know additional fire protection is required between a garage and living space. So is this feasible, or just a crazy idea?

Assuming I'm not already a crackpot, please consider another variation. For this particular house, a second tandem parking spot is easy to imagine in the basement in front of the existing one-car garage. But it might be preferable to use the existing narrow garage as an entry, with angled parking for a second car. But that would seem to require eliminating at least one of the support poles in the basement. Could a steel beam replace one or more support columns? Generally crazy idea, or just crazy expensive idea?


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Garages are commonly placed under houses. The required fire protection of the garage ceiling is generally minimal, usually a drywall ceiling. Some jurisdictions require protection of the supporting posts.

Usually one car goes on each side of a steel support post. A steel or LVL beam can transfer the load of a post to other posts or the foundation.

Tandem parking is not usually a good idea.

    Bookmark   July 9, 2012 at 1:37PM
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Thanks Renovator8. Any comment re: cutting the opening into the foundation wall? I'm guessing the wall would treated similarly to columns... i.e. steel beam to transfer the load across the new opening?

If any part of the basement would be used as living space (not sure if that would include a laundry area), would additional fire protection be needed? I vaguely remember something about change in level required?

Forgot to mention -- foundation is concrete, and house is mostly brick, except for some wood in 2nd floor gable.

    Bookmark   July 9, 2012 at 2:13PM
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Most residential codes only require one layer of drywall between a garage and an adjacent habitable space. That doesn't qualify as a fire-rated wall but it might be considered a smoke barrier.

A door from the garage is not allowed to open into a sleeping space and no egress path can pass through the garage.

Often a small curb or step down is required into the garage to encourage heavier than air gasoline vapors to not enter the house.

If you want to design a house you should buy a copy of the building code that actually applies to your project. Where is the project located?

    Bookmark   July 10, 2012 at 1:27PM
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Not a 'real' project (at least not for me). It's in a Boston suburb. I have a slightly out-of-date Code book, which I use for interiors, but I defer to architect or structural engineer when needed.

Would love to find a forum where architectural issues are discussed, in order to expand my knowledge in that area. For example, while I would use a house inspector prior to closing on a deal, I probably would not bring in an architect until the deal was closed.

    Bookmark   July 10, 2012 at 4:06PM
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I would love to be able to park the cars in the basement.

    Bookmark   July 13, 2012 at 2:50PM
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I grew up in a hillside ranch w/drive in basement. The garage was at the same grade as the rest of the basement, but there was a cinderblocknon-bearing wall between the garage and rest of the basement. I'm not sure if that was supposed to be fire retardant.

I love that design! I live in a totally flat city so I can never find it here. To me, it is the most logical use of space and best bang for your buck.

That house was built in 1971 so codes may have changed since then in regard to having a step-down into the garage.

    Bookmark   July 13, 2012 at 9:54PM
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A home inspector will usually only document deficiencies that might prevent you from buying the house or force the owner to lower the sale price. He/she might have little or no professional design experience or training. If you want to make major changes to the house, an architect should see it before you buy it and he/she could provide an engineer if needed. I often get asked to do that in the Boston suburbs.

The biggest issue I can think of is the cost of adding a retaining wall in order to expose the "garage" wall and the possibility that the existing foundation footing at that point will not be 4ft below the new exterior grade. You should be able to look at the original construction documents at the city/town building department to get an idea of the existing foundation design and you will probably be asked to expose the existing footing.

You will also have to deal with the fact that the edge of the existing basement slab will not be directly supported on the cut down foundation wall and the existing slab will not slope toward the new door for drainage.

The Massachusetts "8th Edition Residential Volume" is available online (see link below). The code is comprised of the 2009 International Residential Code (IRC) and a separate package of Massachusetts amendments to the IRC. The Amendments essentially turn the IRC into the old MA code. If it had been possbible to make the code more difficult to read they would have cone it.

Massachusetts has always made exceptions for existing buildings so pay close attention to APPENDIX J - EXISTING BUILDINGS AND STRUCTURES in the Amendments. In addition to all of this information being online, the IRC is sold by the International Code Council and the Massachusetts amendments package is sold at the Statehouse Bookstore (617-727-2834).

In what city/town is the house located?

Here is a link that might be useful: all MA building codes

    Bookmark   July 14, 2012 at 7:03AM
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Thanks, Renov8 -- I didn't know you were in the Boston area. If you're interested, I'll contact you (off-forum) the next time I have a 'real' project with architectural issues. I am just finishing up a project where the builder chose the architect, and neither of us were particularly happy with the choice.

    Bookmark   July 15, 2012 at 6:01PM
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    Bookmark   July 20, 2012 at 5:41AM
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