In message , Theo
writes
Harry Bloomfield, Esq. wrote:
Upper floor is smaller than the ground floor, so there is a triangle of
space below the windows, maybe with a 2 or 3 foot base.

He cannot add insulation inside plasterboard walls, because of built in
furniture. What is the usual method of insulating such spaces please?

We've just bought a place like that. There's fibreglass insulation between
the ceiling joists of the ground floor, and the vertical walls of the first
floor are backed with fibreglass batts too. I'm not sure what the state of
the upper roof is like, but we'll find out next time we have to replace
the flat roof on the dormer. There are hatches to access the spaces.

I'm pondering putting some insulation between the rafter (with a suitable
air gap from the tiles) to add a second layer (partly to keep heat out), but
will probably want to see how it works over the seasons first.

I have been *doing up* a 1995 chalet bungalow over the last 2 years (not
full time:-)
There should be a small *loft* area over the upstairs rooms which gives
access to the space between the rafters and the plasterboard. Building
control like at least a 2" air gap between the under tile felt and the
top of any insulation but I managed to get 150mm slabs of Rockwool to
slide down the slots. As others have said, there needs to be a vapour
barrier on the warm side.
Our extension was *shell only* so I was able to fit the insulation
before stapling up the membrane and fitting the plasterboard. Skimming
the whole of our upstairs cost £800 so stripping out and re-fitting may
not be hugely expensive.
Cutting Rockwool was done using a handsaw with the teeth ground off and
a sharp edge maintained with a coarse grit stone (garden sickle job).

--
Tim Lamb