"River Tramp" wrote in message
. ..
I would have said that to achieve 30min FR with a ceiling of 9.5mm pb, you
need t & g boarding, and the floor void needs 60mm mineral wool on chicken
wire mesh stapled to the joists.

According to British Gypsum White Book (Section c60 page 5), min 18mm T&G
boarding, 47mm thick joists at 450c/c and 9.5mm wallboard with 2mm skim finish
gives 30 minutes FR. No quilt is needed.
http://www.british-gypsum.com/PDF/c60_093.pdf

For FR purposes only, in the voids you
could do away with the boarding and use 100mm mineral wool instead (but not
if sound insulation is required).

We also would not accept the FR door into the voids; inlike some BC
authorities, we required the entire floor eaves to eaves to have the full
fire resistance.

That's what I would expect too. I'd be surprised if any extra fire resistance
is needed in the voids.

Peter