Hello, and good idea for a discussion. Things are a bit up in the air for me, but my build timing will probably be pretty close to yours.
Your climate is more moderate than mine, but it's still cold, and I have some real concerns about cob for building full time residences in the north, and the possibility of creating a pretty high impact home just through the long term
energy requirements for heating. I do love the aesthetic though, and I'm thinking it might be possible to have the best of both worlds...
I have started looking at some ideas around insulated modified earthbag building. Some possibilities are scoria or pumice fill, but it changes the structural dynamics of it all a bit. Owen geiger's earthbag building blog has great free info and links on some insulated earthbag ideas.
webpage
For what it's worth, here's what i'm thinking in a nutshell:
- rough
wood pole 'henge' supports reciprocal rafter roof
- wall structure is three or four rings of re-purposed metal grain bin, it is not load bearing
-external wall is insulated 'earthbag' tied to to the bin wall, i have found a source of recycled polystyrene to use for the fill...this will be earthplastered where exposed, and heavily bermed to the north
-internal wall is cob and earth plaster, probably 'keyed to the bin wall with
chicken wire or such, this will give some thermal mass inside the insulation shell
roof insulation will be more bags of recycled polystyrene above the ceiling / reciprocal rafters, followed by felt,
pond liner and green roof..
- heat is passive
solar and
rocket stove mass heater
- earthbag / rubble trench insulated shallow foundation, and insulated adobe floor
it
should look hobbit house-y.....to get a reasonable living space i'll probably split a grain bin in two, to make two roundhouses joined by a very short earthbag vault...
'wing-nuts-R-us' i guess, but it seems like a reasonable solution for a low cost, warm, DIY dwelling...
cheers