I don’t believe this is particularly common, but we’re planning on building two extra rooms in our basement by excavating the space under our garage. In a typical garage, the floor is simply a concrete slab that sits on top of soil, however we’re going to approach things a bit differently.
Because our foundation will be built with ICFs, we’re planning on utilizing a “deck” system that will integrate a structural concrete slab directly into the foundation itself. This means we’ll be able to pour concrete for the foundation walls and the garage floor at the same time. When everything cures we’ll have a structurally sound garage floor capable of supporting the weight of a car, plus a completely insulated 10×20 space below it.
The decking system is pretty straightforward to install—Once the ICF blocks have been assembled, the foam deck panels are placed across the span that makes up the garage floor. These panels are then supported from below with temporary shoring and reinforced with rebar.
Obviously this approach is going to cost a little more, what with the additional concrete and rebar and foam panels and labour, but we’ll be gaining an additional 200 sqft of space that would have otherwise been inaccessible. If you take a look at our floor plans, you’ll see that we’ll have a very generous “study” and additional storage down there… which I’ll say is a decent use of that space, no?
For those itchin’ for the nitty gritty of how a system like this is installed, I also dug up a PDF aptly named Pouring A Structural Slab that explains it all.
looks to me like you’ve elected to your basement hight make more above grade than is traditional. i’ve always thought that would be a good idea to maximize window exposure. i was thinking more like 4’ above grade but maybe that just puts the hight requirements on the entire house just out of bounds?
thanks for documenting your process here. i’ll be following with interest.
We’re aiming for very generous ceiling heights in the basement – We’ll actually have 9’ in the back, which is huge for a basement. We actually wanted to set them a little deeper, but the proximity to our neighbor made this impossible (unless we added addition shoring, which would have added greatly to the cost of the foundation).
The only problem with building the house 4’ above grade is that you need to then have more steps into the house… Instead we tried to strike a decent balance and extended a little above grade. We wanted to get as much natural light down there as possible, so we’ll be adding large windows in wells to accomplish this.
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