Richard wrote:

Do you mean there is no wall in the loft between each terraced house?

Yes

[...]

Any ideas for board material, stronger and lighter than chipboard (to
reduce the stress on the joists/roof?). FYI the ceiling joists are not
resting on the wall plates, but are constructed so that they are fixed
to the (substantial) rafters which sit on wall plates. This means
there are sloping edges to the ceiling that I havent yet worked out
how to insulate behind the lathe and plaster, due to lack of access -
any ideas how to finish these?

I'm puzzled by the construction here... how come there's no wall between
you and the neighbours up there, but apparently there *is* a finished
lath and plaster ceiling over the rafters?! Or am I missing something?

David