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Elevated floor over FPSF

Christopher Solar| Posted inGreen Building Techniqueson

I have a 100-year-old house in Ottawa, Ontario and I want to build (re-build, actually) a one-story addition of about 130sf. This is zone 6 (by US standards) and the AFI is just over 1800 degree-F days.

Getting excavation equipment to the site would be difficult, as the house is on a small urban lot and the back yard is hemmed in by fences, porches, etc.. The idea of a frost-protected shallow foundation (FPSF) as described in Martin’s GBA article (//m.etiketa4.com/system/files/sites/default/files/Frost-Protected%20Shallow%20Foundations.pdf) is appealing. I have no need for a basement under this addition, so a slab on grade sounds like it would do the job with minimal digging.

One thing I’m wondering about though: the finished floor for this addition will be on average about 36″ above grade, in order to match up with the rest of the house. I assume that means I need an independent slab and stem wall to elevate the floor framing (as opposed to the monolithic slab version). What, then, is the best way to deal with the gap between the underside of the floor framing and the top of the slab? Would it need to be accessible from the interior?

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Replies

  1. GBA Editor
    Martin Holladay||#1

    Christopher,
    Q. "What, then, is the best way to deal with the gap between the underside of the floor framing and the top of the slab?"

    A. I think you would call it a crawl space.

    Q. "Would it need to be accessible from the interior?"

    A. You could provide an access door from the interior or the exterior. It's your choice.

  2. Expert Member
    Malcolm Taylor||#2

    Christopher, Since the addition is that small, have you thought of building it with concrete sono tubes and not having either a slab or crawlspace?

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