The topic of this program will be the Structural Concrete Design and construction of a two level detached three car garage on a steep building site overlooking Bozeman, Montana.
This two level garage features 900 sq ft of living area below the structural concrete parking slab.
I will focus on some of the building site issues that influenced my design decisions. I will also show some of the construction details needed to implement a structural concrete design that safely supports the weight of three full size vehicles.
Design Issues
The decision to use the Structural Concrete Design to create living space below the structural concrete parking slab was determined by two factors. I needed to keep the parking slab at the same level as the main house despite the fact that the lot falls away from the building footprint.
The other determining factor was the expense of bringing in a large volume of compactable backfill was almost equal to the added cost of constructing an actual basement.
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I modified the design to be basement walkout, and hired engineers to ensure the structural concrete design was sound.
Construction Techniques
We put slope on the slab by forming a ledge around the top perimeter of the foundation walls. We also formed beam pockets to catch the steel I beams.
The beam pockets and perimeter ledge we had formed into the walls made for an easy installation of the steel decking that would contain the structural concrete slab pour. Both upper and lower slabs contain pex tubing for a future hydronic heating system.
Critical components to this foundation are a quality waterproofing membrane, closed cell foundation wall insulation, and a good footing drainage system.
Our finish detailing was clean and this three car garage with an apartment / shop below is a nice compliment to the main house and a very valuable asset to the new owner.
Really great, Peter! Very professional; you could be on TV with the guys.
I don’t think I’d want to have an apt. beneath a garage (fumes, maybe)? We had
living space above a garage here before we bought this house, and I’d never do
that again. But understand your site challenge here.
What a great design! In Tucson, Arizona we really don’t see basements to often but the extra room under the garage is a nice complement to the rest of the house.
Well I think thats true but most of the time people ignore that kind of advice.
Hi Peter: I just watched your video on the 2 story garage – beautiful project! I recently designed a 2 car detached garage with living space below in Calgary Alberta. The cribbing is now completed, but there is some controversy over how best to vent the warm air from the living space below the slab. This floor system is comprised of engineered wood floor joists supporting the concrete slab above. Do you have any advise on the venting issue?
Thanks,
James
Nice video. Good Work Mr Brown.
Peter, Very impressive design and use of space and materials.
I am planning a garage on a sloped lot in Colorado; a two-car garage with a single car space under it. We have large rocks that don’t allow space for a wider three-car garage on one level. You placed the metal panels over the steel beams. Were there temporary support structures under the metal when you poured the concrete? What about 24″ wide prestressed concrete floor panels? I will only have a 24′ square garage with a 12 X 24′ lower bay. I guess I need an engineer. Any thoughts?