Basement, crawl space, none of the above...?

15 Jun 2017
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United States
Hey guys, I am working on a new construction home in Colorado and have done most of the drawings myself. I really love a slab floor and it is one aspect I don't want to bend on. Most of my professional work is in concrete and the home has a lot in it. All of the exterior walls are full height cast in place and there is also an arched concrete vault ceiling. Think Guastavino.

After inspecting the site and soil, I assumed, incorrectly, that I could use a foundation wall on a spread footing along with a floating slab on grade. Well the official tests are in and the soil is too expansive to accommodate a slab on grade. Bummer. My only real option now is to install caissons and a structural slab. $$$

Well, not all is lost. The footers and foundation wall don't have to be built now and I can neatly hang my utilities under slab while other areas are being worked on. Building the slab on void and burying the utilities seems like the worst of both worlds, and I'm not a fan of post tension cables either. My thoughts are, "If I have a structural slab, I might as well have a space to access utilities and store stuff.". Here is a cross-section showing a proposed crawl space. Overhangs are not shown, but will extend at least 5' from the exterior wall. Dutch gable roof or gablet for you Brits.

Now, a lot of people will point out that I might as well build a basement, but this is a single story ranch with a lot of square footage(5200sqft not including mezzanines). Excavating, building basement walls, and pouring a basement slab would just break the budget.

My question is this. Can I build a crawl space like this with sloped dirt closing up the space? I would install a sump pump, small vent fan, and insulate the slab edge. This isn't really a basement or a crawl space exactly since there aren't any "walls" but I've never seen this done. Even if a little moisture made it past the overhangs, sidewalk, and vapor barrier, what's there to rot?
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DanRichNC, good evening.

You possibly do not realise it but, you have posted on a DIY site that is principally used by users in the United Kingdom, the regulations that you live under are far removed from ours.

It is my opinion that your post will not be answered meaningfully very few contributors to this site have the requisite background to provide a meaningful response.

Don't see why not as long as it's ventilated it's just the same a a normal suspended floor.

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