geo-dome home foundation

If things go as I hope they do, I plan on building a geodesic dome home around October. This home will be built out of steel for the frame, not wood. My questiion is, which way to go for a foundation? For a geo-dome, all you really need for a foundation is the outer circular area. Since there is no weight anywhere else to consider.
Let's say I do a four foot wide circular cement slab. What can I use in the rest of the area not cemented? This will be in northern florida.
My other option is to do a crawl space. In the steel version, standoffs are what are cemented into the ground. Then the frame is connected to them. In that case, I want to have the outer wall shaped as the dome. Then a series of inner walls for support of the floor. But how many? The maximum width of the house is 48ft. Considering using 2x12's on top of the cinder block inner walls. What's the largest span I can get away with? 8, 10 or even 12 foot?
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wrote:

Can't you use steel for floor joists? Down in Florida, like the Texas Gulf Coast, don't you have a rust problem with steel?
<><><><><>< It now takes me all day long to do what I used to do all day long.
The Quartermaster
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I would build a perimeter foundation for the structural part of the dome. I would build a floor system that would support interior walls and floor. Using 2x6 joist, (those could be used for the foundation framing and cleaned and re-used for the floor) You could set up piers and 4x6 to support the 2x6 floor joist. This is a standard way of building for either geodesic, and or rectangular raised floor. A concrete slab allows water to run in and under attachments and I would keep my foundation separate from the exterior concrete work or whatever.
A person could also use metal in lieu of 2x6 joisting. A person could use TJI joist for greater span and lesser support. I like 2x6 since it is economical, re-useable, and with a dome, you have many cuts to consider. Also if wanted it could be PT for insect. Consider too, you have crawl space for plumbing and electrical. john
"richard" wrote in message
If things go as I hope they do, I plan on building a geodesic dome home around October. This home will be built out of steel for the frame, not wood. My questiion is, which way to go for a foundation? For a geo-dome, all you really need for a foundation is the outer circular area. Since there is no weight anywhere else to consider.
Let's say I do a four foot wide circular cement slab. What can I use in the rest of the area not cemented? This will be in northern florida.
My other option is to do a crawl space. In the steel version, standoffs are what are cemented into the ground. Then the frame is connected to them. In that case, I want to have the outer wall shaped as the dome. Then a series of inner walls for support of the floor. But how many? The maximum width of the house is 48ft. Considering using 2x12's on top of the cinder block inner walls. What's the largest span I can get away with? 8, 10 or even 12 foot?
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On Mon, 30 Jul 2012 08:26:34 -0700, jloomis wrote:

That's kind of what I had in mind. Since the main floor is nothing more than a huge deck, I think using 4x4 posts implanted in the ground would suffice. But I think I would use at least 2x10's across the 4x4's.
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Concrete Piers are poured first. Sometimes Simpson brackets can be used in the pier pour. I make my own piers with tar paper rolled in a circle. I dig a footing, pour concrete in the footing, then put the ring on that and fill it. I then put a piece of 2x6 with 16's embedded in the bottom. This goes on the pier for post attachment. Never put 4x4 in ground. Use girders on those posts that stand on the piers. 4x6 for 6 ft. span. larger span, larger girder. I could draw up a nice concrete plan for main footing and floor. I always overbuild. One would first dig and form the main footing. Then one could pull lines from that, dig piers, and pour the entire foundation at once. The girders support the floor joists, which support the subfloor. I also pay attention to above walls, bathroom walls for size for plumbing, and any bearing walls. Those should be poured as a concrete footing which would support main loads above. Using pressure treated under building is a good idea for insect/termite/ Also venting the subfloor is important, a crawl space, and even lighting under floor for work. Some even put a plastic vapor barrier down and then"P" gravel on that to make it easier to move under floor and hold the plastic down. This keeps moisture down, and makes it much dryer under the floor. Lots of thought goes into the foundation and floor frame. Using glue on the subflooring is important too. And nail size and schedule for attachment. Good luck jloomisconstruction.com
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On Mon, 30 Jul 2012 08:26:34 -0700, jloomis wrote:

That's kind of what I had in mind. Since the main floor is nothing more than a huge deck, I think using 4x4 posts implanted in the ground would suffice. But I think I would use at least 2x10's across the 4x4's.
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