I thought I would speak to Ecology Building Society to see what mortgage might be available so I could bottom out my build budget. I did them a fairly detailed email explaining that I was plannning straw bale construction, probably off grid, outlining my likely budget, salary and equity. Here's their reply:
Thank you for the enquiry
If you would like to discuss please call us on 01535 650770.
Not quite clear on your project,However our income multiples are as follows- 60% loan to value = 3.5 x income
80% 3 x income
85% 3.5 x income
Nothing more, nothing less....
I rang them just now and after being put on hold for a while, a polite lady came and said my house must have good insulation and not have any pvc windows otherwise I would not qualify. She walso asked my what the house was worth now.

I rang the Co-op, but hit a brick wall. No strawbale lending there which was surprise in a way.
I will have to have a trawl for other lenders, but would be interested if anyone can think of any!
Ta.