How can I insulate above the ceiling of my converted loft?

[Fred178]

Hi,
I have a converted loft. It has stud walls, a sloping ceiling, then a flat ceiling at the top. The Roof is slated and has some sort of membrane above the roof joists. The roof also has 4 ventilation points on either side. I have insulated the back of both stud walls, the 'floor' (ceiling of the room beneith) behind the stud wall and across the underside of the roof joists.
It's warmer than it was, but it's still cold. Last winter the bottom half of the roof had snow on it far longer than the top half.
I want to insulate the top half of the roof. This means behind the sloping ceiling, and above the flat ceiling. Is there any way to do this without removing the plasterboard?

 

[noseall]

Yes.

You can achieve the same result by removing the roof tiles, membrane and lathe and do it this way.

However i would suspect it is simpler to remove the plasterboards and do it from below.

If head-room were not an issue you could consider fixing foam board insulation to the underside of the existing plasterboard but this would still leave you with the headache of plasterboard and skim.

 

[lowster]

I had a similar dilema - building regs stated that I needed PIR insulation on a sloping roof. I don't believe there's any other method for fitting this other than what has already been mentioned (take the tiles or the plasterboard off) I opted for ripping out the existing plasterboard - to make it worth while fit a minimum of 100mm insulation. One point to note is the depth of your rafters, mine were only 75mm so we had to fit battons to accomodate the additional 25mm. We were also advised by building regs to put 25mm PIR backed plasterboard to prevent any cold spots from the rafters.
Unfortunately there's no easy fix - it'll be a messy job, but if you can do the labour i.e. rip the old boards out and fix the new then it won't cost you too much to do. The only expense really is the insulation itself (PIR aint cheap!) and the cost of a plasterer to skim afterwards.
P.s I'm not expert, but if your roof felt isn't breathable (old black tar like material) you will need to leave a minimum 50mm vent gap between the felt and the insulation - also you may need to get some mushroom tiles for additional venting. I was warned that without sufficient venting condensation can be a real issue.