A friend has a 1960's chalet style semi-house, where the first floor
bedrooms are always cold. Gutters are at ground floor ceiling height.
End brick wall goes up to roof and is CWI. Upper floor windows are set
in the roof slope and have no internal cills. There is CWI at front and
rear, up to roof gutter/roof level.

There is no insulation at front, or rear, between plasterboard wall and
angle of tiled roof, which makes the place drafty, cold and expensive
to heat.

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?

I have suggested the only way is to gain access via tile removal and
fix thick insulation between timber frame to rear of plasterboard. Or
maybe a spray on insulation foam added to rear of pasterboard.

Enquiries with insulation specialists have produced little interest.