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.
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.
I modified the design to be basement walkout, and hired engineers to ensure the structural concrete design was sound.
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.