insulating cathedral roof

[Ninja Chris]

Hi, I have a cathedral roof with 150mm joists and gib over the joists. I want to insulate it so I've screwed battens across the bottom of the joists and blocked out between them so that I can screw sheets of gib up. I intend to pack the space with pink batts but I don't know what to do about the existing ceiling. Should I knock out the old gib, which will be above the pink batts, to allow any moisture to evaporate into the roof space or can I leave it there? I intend to seal and paint the new gib so I think this won't be a problem.
Thanks,
NC

 

[theprinceofdarkness]

What is gib?
Frank

 

[noseall]

What is gib?
Frank

 

[stuart45]

What is gib?
Frank

Aussie plasterboard.

 

[theprinceofdarkness]

The lowest layer in any roof construction should be vapour proof. Any intermediate vapour roof layers would only trap moisture because the void would be sealed with little air flow.
Frank

 

[Tipper]

The lowest layer in any roof construction should be vapour proof. Any intermediate vapour roof layers would only trap moisture because the void would be sealed with little air flow.
Frank

Does not the location of the vapour barrier depend on whether you are keeping heat in or keeping heat out, ie, if you are heating internally or cooling with air con?

 

[Ninja Chris]

Thanks POD, that's what I suspected. I'll drill some holes in the existing ceiling before I put the insulation in so moisture can evaporate out.
NC