WHAT INSULATION IS SUITABLE FOR A BATHROOM CEILING??

[new DIYer]

CAN ANYONE ADVISE ME ON THE BEST TYPE OF INSULATION FOR A BATHROOM CEILING?

Hi I have never done any plasterboarding or insulation before and have spent hours trying to find info and just getting confused- Please bare with me!
So, i have a pitch slate roof max20cm above the pitch bathroom ceiling and there is only 10cm between the ceiling and top of the window frame-not much space for insulation!

I have gathered ( i think) that the best solution is to put some kind of thermal board between the joists, and plaster board to the underside of the joists. This I can do if it really is that simple.

But with so many types of board I have no idea which one I need and whether they are suitable for bathrooms.

Can thermal board be wedged into the gaps between the joists as has been suggested or do i need to make extra battens to screw it to?

I have read about the need for a vapour barrier but don't even know what that is- eek- sorry for my ignorance but i need simple advise in laymans terms!


Am i also to assume that if i leave a gap between the top of the insulation and the roof, then that will provide adequate ventilation?
I have no loft space above obviously so all work has to be tackled from below.
Sorry for all the questions which i'm sure are blatantly obvious to most people but i'm new to this!

Thanks in advance! Ally

[TheDoctor4]

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