insulation question

[Stuart Noble]

I need to put some insulation above a dormer window which projects about 2.5 metres. Because the opposite wall is sloping I have no access to push celotex between the rafters without breaking it down into several smaller pieces. The problem is compounded by the fact that it's a lath and plaster ceiling, so the surfaces between the joists are not smooth.

One possibility is to pack Rockwool into the space but this would leave no ventilation. Or maybe I could use the foil faced bubble wrap stuff, but I still don't see how I can push it that far without some sort of stick. The roof of the dormer is zinc or lead (I can't really tell from the inside) and below that are some thin pine boards, and then the joists.

I know I should take the lath and plaster down but, having done that in other parts of the room, I really can't face it. There's no room to insulate on the inside because the window is right up against the ceiling.

Comments appreciated.

[Phil L]

Why the aversion to sticks?

If it will go down with a stick, use a stick, if it won't, then you need to take down the L&P....I favour the stick....keep the insulation elevated so that it slides underneath the boards rather than snags on the plaster snots, and a length of plastic wastepipe is better than a wooden stick, especially if you cut the end into a 'crown' effect first. ;-)

[Stuart Noble]

Because of the angle, anything straight can't be more than a foot long, but I reckon I could just keep feeding rockwool in there till it was full. The only thing I'm worried about is having the fibreglass tight against the roof/joists/plaster with no circulation of air