My bathroom is on the 1st floor at the back of my victorian terraced house, and as such has it's own small sloping roof separate from the main roof.
I am about to gut the bathroom completely as part of ongoing renovations, including taking down the ceiling and replacing it.
Currently there is an ageing ceiling which appears to be made of some sort of plaster, above that there is a small gap of a few inches, and above that the roof tiles - no insulation whatsoever!
I of course want to insulate as best I can before putting up a new plasterboard ceiling.
Since space is tight and I do not want to lose headroom I was planning to use solid insulation boards (Kingspan or similar), probably 100mm thick, between the roof tiles and the new ceiling.
So my question is, is this the best solution and if so what should I do about moisture?
Do I need to use a vapour barrier to stop moisture from the bathroom from forming condensation on the insulation panels?
If so I assume it would need to go beneath the insulation, right?
And how would it best be joined where it meets the walls?
Any advice would be appreciated!