In article ,
Jon writes:

My parents recently had a single storey flat roofed extension
insulated. (Built in 1964, originally just foil backed board
and strawboard roof as insulation. Strawboard had been
replaced with ply.) I wasn't there, but I understand
they took down a strip of plasterboard along the centre
of the room perpendicular to the joists, and slid more
solid fibreglass bats along above the ceiling to the
edges. Ceiling was then repaired and the room was to be
decorated anyway.
I'm not too worried about the finish as the ceiling is only in the
garage. The trouble is there is already some poor quality loft
insulation in the void and I would have to get that out first before
putting in the rockwool, which could be a problem.
Nice idea about cutting out a strip of plaster though and pushing in
the new insulation. Removing all the plasterboard will be very messy
and I don't fancy it at all, but it needs must ....

BTW, the removed strip straddled the nogins, so they could
push the bats up either side to both edges.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]