Vapor Barrier above insulation on flat roof

[Steebi87]

Hello, 

 

I'm currently in the process of insulating and boarding a lean-to roof and was just wondering with to add vapor barrier above the insulation, or does this cause any sweating below? I've added an image below of what I'm in the process with.

 

Thanks in advance

 

 

[nod]

It is likely to cause separating above 

The modern way would be to use a duplex plasterboards 

(foil back}

[tonyshouse]

Do not under any circumstances introduce a vapour barrier on the cold side of your insulation - yes sweating, staining and rot 

[Steebi87]

12 hours ago, tonyshouse said:

Do not under any circumstances introduce a vapour barrier on the cold side of your insulation - yes sweating, staining and rot 

 

That's what I was thinking, just wanted a second opinion. I was originally planning to seal round my boarded insulation (kingspan/celotex) with expanding foam or something. I'm guessing this could also be a bad idea? 

 

Thanks for your help! ?