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Cob hemp dome

Posts: 1
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Hey everyone. Please let me know what you think of my most recent idea-in-process:

Location: either the northeast(Maine) or Colorado. \

A small 15' diameter, maybe 20' ( how big do you think I can get away with?) domed structure made out of cob (clay dirt, sand, straw(or hemp?). How thick do the structural walls need to be? What are the pros/cons of building a bamboo, hardwood sapling, or rebar skeletal frame for this? Is it necessary?

There will be a RMH exhaust running through a bench,as is traditional, but also will spiral upwards through the walls of the cob dome. How much will the 6" or 8" exhaust pipe affect the structural integrity of the dome?

On the exterior of the dome my idea is to use hemp grown on property (which apparently is legal now in CO with a permit). I was thinking why not figure out an efficient way to either bale it or chop it up and cover the whole dome in a foot or more of this mixed with some clay slip (or lime, which I don know much about yet), or some type of earthen plaster, any recommendations? And if not hemp, then can this be done with a different plant that can be easily grown in quantity, like stinging nettle or evening primrose, or straw, for example. After thorough drying.

The entire structure would be covered with metal roof with large overhang. Can I use cob pillars to support the metal roof to avoid using timber since it may not be available to cut.
Thank you very much.
Posts: 65
Location: Columbia, Ky
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Hey Michael,
Great idea you have their! I haven't actually heard of anyone building a cob dome but maybe you could consider an earth-bag dome which is very common. Check out Cal Earth's webpage for more info on that.

As far as cob pillars holding a load check out this youtube video of the Cob Castle
The entire structure is held up by cob pillars. I don't know any formulas for how big they must be for what weight etc but just over kill it and you'll be fine .

Good luck!

Posts: 684
Location: Richmond, Utah
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Also, you could check out Nubian vaults from adobe like Hassan Fathy is known for. I've done a lot of metal roofs, but I would be scared of installing metal on a dome. Lime plaster is all you need!
Posts: 68
Location: Essex, UK
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Are you supporting the roof independantly, or is the cob supporting the metal roof? This latter doesn't seem right at all.
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