you mean a icf concrete form your roof is not 4hrs though unless your putting on alot of weight the walls maybe that rating dosnt mean the rest of the build isIt's the back garden. The original plan was 350mm from the boundary which is where the existing garage (to be demolished) is built. that might change to 600mm now as a show of good faith and allowing me to work without diturbing their fence.
Concrete form is planned to be Nudura from here. Re the fire rating, I emailed the supplier saying I had recieved an objection commenting on fire risk and could he advise as we'd mentioned fire ratings in passing previously. He emailed me back a certificate showing it to be 4 hours for their 6" core with 10mm rebar at 400mm centres vertically and 487 (I think) horizontally and 12.5mm plasterboard on the internal face
your sound proofing is also poor as it will resonate like a git in there