Does anyone have any experience or knowledge of building self-supporting roofs in strawbale? A neighbour want to build something pretty much the same as this...

http://www.skillful-means.com/projects/vault/lou_harrison.htm

I've emailed the architect and the owner with a couple of questions, but got nothing back from either. I've put the questions below just in case anyone can advise.

Many thanks.

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1. Could you give me some details about the materials you used to cover the building to protect it from the weather? I'm thinking of using a layer of lime render, then a breathable waterproof membrane, then a layer of lime render with waterproofing additive. Do you think that would be long-lasting and resilient? Our winters here are wet, with regular frosts and snow.

2. As the extension will be attached to an existing stone building, I'm planning on building the vertical walls using a local sandstone. Can you forsee any problems with sitting the same strawbale vaulted roof on top of stone walls?

3. How long did you wait between removing the forma and applying the render? Is there much settlement movement?

4. From reading the website, I'm a little unsure where the rebar sits in relation to the mesh. Is the rebar between the mesh and the straw, or the other way around? *** I think we've got this one covered now. The rebar sits between the render and the mesh. ***

Ah yes, apologies. In southern Italy. 250m ASL, summer temps reaching 48, winter regular frosts & snow, high humidity year-round. The project is an extension to an existing house, made up of a series of stone-built trullo cones.

ETA: And yes, I think it would be very useful to include a bit of profile information on each post. I appreciate this is a predominantly UK-based forum, but there is so much information and expertise, it's hard not to use it from abroad.

Might be better to look at using some kind of timber cladding for the top of the roof, using some kind of capping material like zinc flashing for example or possibly roofcrete.

Using metal rebar in strawbale walls is considered a bit of a no no because it can cause condensation problems. This is certainly the case in Europe, the US has a history of using metal rebar and mesh aswell as concrete renders on strawbale, I dont know if they have changed their approach now. Bear this in mind when reading material from the United States, especialy hot dry places like Arizona.
It would be possible and better to use a timber frame strucutre in place of the rebar, something like larch for example.

No real problems with building on stone walls except for possible condensation issues. Need to think about possibly breaking the contact of the bales sitting on the walls with something like an insulated and vented box beam made from OSB or ply.

settlement will depend more on the nature of the undelying wooden frame structure.
My advice would be to dip the inner and outer surfaces of the bales in a clay or lime slip before posing them on the frame work. This will act to strengthen the vault and counter act shearing forces , keep unwanted wildlife out, add thermal mass and provide a good level of fire proofing. It will also "set " the strucutre so that settlement effects are reduced.

bare in mind that the arizona house was built nearly 14 years ago, so there is potentially alot of change since then. I'd recommend speaking to The Amazon Nails - top straw bale folk!

Yes, speak with Amazonails if Poss, but also be aware that load bearing design as I knew it a couple of years ago isn't accepted in Italy if for a living space. Best of all to be in touch with the Italian maestro Stefano Soldati who built the first self built straw bale home there. www.laboa.org.