No subject

build the roof of a house first, at ground level, and then, somehow, build the rest 
of the house underneath it. Straw bale houses, with their forgiving nature, 
somehow seem appropriate for this sort of thinking. I came up with several ideas 
- jacking it up; flipping it over onto the built house; rolling it; 'pole vaulting' it, etc. 
But in the end I concluded that, in fact, there is no real advantage in doing it at 
all. It's no easier, it's no quicker, it's no cheaper, it's no better. But it was fun 
scheming, and who knows, maybe I'll try it out one day.

I quite agree with you that load bearing structures make more sense in many 
respects, rather than just in-filling a timber frame. But then timber frames have 
their place, too. But I would worry about the spreading load in the lower courses 
of bales. I'm pretty sure that the pressure within them will not be simple and 
vertical, but will involve spread out sideways, too. A possible problem with this is 
that if one starts to splay out, the surrounding bales will not have the rigid, 
interlocking stability to support themselves like bricks (for example) would. A 
single collapsing bale low down, in a key position like a corner, could end up 
bringing the whole structure down. Remember that block of flats that collapsed in 
London(?) in the 70s(?) - a low level structural failure brought them all down like 
a pack of cards; they don't build towers like that any more. 

20 metres is one hell of a four story building. Even allowing for a pitched roof, 
this is still 12+ foot ceiling heights. There is going to be huge weight bearing 
down on the lower bales, and keeping the all straight, level and even will be 
absolutely imperative. Building from the top down will mean that you get to lay 
the least stressed bales first, so your experience, ability and understanding of the 
structure will increase as you get to the bits where that counts more.

Jacking it all up as you go - well of course they build some concrete tower blocks 
that way, so it's a proven technology, it's certainly spectacular, may be quicker, 
may be more fun, and who knows, may be more practical. Site insurance, 
including public liability, may be a problem.

Rendering a storey at a time and then jacking? Things *will* move as you jack, 
and without the rigidity and structural stability of 'traditional' materials (ie 
reinforced concrete) cracks are a certainty. You would need a plan to deal with 
high level repairs, and also for the periodic maintenance that lime or earth 
renders require.

As I said further up, I have absolutely no experience of strawbale building yet, so 
I've absolutely no business in spoiling your party. If you can deal with the 
challenges, what a fantastic thing to do.