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Discussion Starter #1
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? The forum is not allowing me to post links to the pictures yet even though I've had 1 post. Will try to reply with pics.
 

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In NJ and never saw one house (all old) with excellently buried utilities - except cast iron main sewer lines. Radiant flooring iron pipes, galvanized hot air duct, copper pipes - all seemed to deteriorate sooner or later, from moisture or concrete cracks. Your floor also will have to be reinforced instead of floating on ground. You have a lot of space under the roof, looks enough for any utilities you would need. Design wise, if you would take the trouble of casting domes, why would you cover it with simple roof?
 

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Thanks for the reply carpdad. Yeah, you're right, the slab will need cast in place beams and joists. The roof is there mostly for aesthetics and resale value, but it will also allow me to run electric along the outside of the vault easily. I'm partial to a vented attic and blown-in insulation is much cheaper for achieving high r-values than foam board. And I can store some stuff up there too. The same concept was used for the Ellis Island Museum.


 

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I know you didn't ask for dissenting votes but, other than an exotic hobby (expensive too) it will appeal to a limited number of people in the price range it would need to command. And that is if you get past the engineering process.

Rich is in the middle of your name and if you have money to burn don't let me discourage you, I've visited the Hurst castle and it is very nice but also out of my price range.

But a more popular way to go is "net zero" a combination of energy efficiency and energy generation. The connection here is that thermal mass can be incorporated into the energy plan of these modern homes and your masonry skills would fit in well.

Bud
 

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Thanks Bud, I appreciate the grounding in practicality. I'm not rich by American standards, and the home honestly won't be as pricey as you might be thinking. A couple appraisals seem to indicate that I could double my money. A lot of that springs from me self performing a lot of the work with co-workers/family and some of the resources and contacts I have through my company. I'm mostly building it because it's been a dream a long time coming, but I don't want to be in the hole if I need to sell someday. I love monolithic domes, but to be honest their resale and visual appeal can be bad. It was pretty foolish to make some plans before the soil test, but I spend a lot of time building foundations and the soil was almost identical to a lot of sites around that have done well on traditional footings. My neighbors aren't on caissons and I think the engineer is just playing CYA.

I checked out some pics on Hearst Castle and I had completely forgotten it existed. Beautiful work!

The Net Zero/off grid concept is intriguing to me and I think a few years down the road we can achieve that. I did some investigating on heating the house with hot water passive solar and a radiant floor, but there were a lot of unknowns and I used a lot of conservative numbers. Basically it came down to a 10+ year ROI. I'm kinda on the fence about it. Penny for your thoughts.
 
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