Retrofitting insulation to sloping roof

[mizunooto]

I'm working my way through my dormer bungalow which was built without a shred of insulation in the 1960s. My biggest problem is the area of sloping roof/ceiling on either side of the dormer windows, i.e. from the (small and cramped) loft space down to the eaves above the ground floor. The property was re-roofed about 10-15 years ago (nobody thought to fit insulation!) So I have a number of "slots" to fill, each about 4 x 20 x 72 inches, and not sure the best method to use. I could try pushing celotex into the slots though it would have to be cut small to ensure I could push it all the way down. I thought of pouring chunky polystyrene loose-fill down the slots - it couldn't escape at the bottom and would still allow some air circulation - would this be sensible or not? Any ideas would be welcome.

[steviejoiner74]

As soon as you insulate between the rafters you'd really need a vapour barrier on the warm side to prevent condensation. This would mean taking down the plasterboard.
Fitting rigid insulation requires a tight fit between rafters for it to be effective as well.
The cheeks of the dormers also would require insulation and the small ceiling under the dormer roof.
This all requires the removal of plasterboard to make it worthwhile and effective.