Ceilings and Airtightness

[Builder9999]

Good evening everyone,
I am building a new timber frame house. We have a "Vapour Control Layer" on the inner face of all external walls (VCL - 25mm service void - plasterboard) to also act as our airtightness barrier.
What is the VCL/airtightness barrier across my first floor ceilings? I have a traditional "cold roof" design. Just the plasterboard???
Look forward to hearing your views.

 

[jeds]

Strictly speaking a vcl isn't required to a cold roof as it should be adequately ventilated. It wouldn't do any harm to instal one though - to increase air tightness.

 

[Builder9999]

Thanks Jeds.
I am thinking more about airtightness or do I rely on the plasterboard? Or perhaps put membrane over plasterboard joints?