Flat cold roof and vapour barrier

[OrangeJuice09]

Hi,
I'm having a cold flat roof installed. 100mm PIR board to be inserted between the joists and some form of insulation with plasterboard will need to be fitted to the ceiling.
I understand a vapour barrier needs to be fitted between bottom of joists (where the 100mm is inserted) and the finish insulated plasterboard of approx 30mm.

I get the impression a warm roof design has become the standard, is a cold-roof design acceptable in building regs?

To my knowledge, the vapour barrier comes on a roll which I can add as a separate item, but if I install a thermal plasterboard does it act as a vapour barrier anyway?

I watched a few video's on the subject and it mentioned that the 'vapour barrier' should not be pierced, if this is true how can a few spotlights be added?

 

[noseall]

Hi,
I'm having a cold flat roof installed

Are you venting It?

 

[OrangeJuice09]

There will be a minimum of 50mm air gap between the insulation and the OBS boards.
Venting strip will be added to soffit. Not sure if Abutment Vent is a necessity so would be grateful to hear views on this also (is there a decent kit on the market) ?

 

[noseall]

There will be a minimum of 50mm air gap between the insulation and the OBS boards.
Venting strip will be added to soffit. Not sure if Abutment Vent is a necessity so would be grateful to hear views on this also (is there a decent kit on the market) ?

You should have through ventilation on all joist runs - which means venting at either end.