Flat roof insulation advice

[wookston]

Hi, I'm hoping someone can help.

I need to insulate my flat roof and have decided to keep the roof as a "cold deck" for reasons that I won't bore you with.

I am planning on redecking the roof and recovering at the same time as insulating it.

my question is where do i put the vapor barrier (below or above the insulation) as I have been told by some people to put it above the insulation and others to put it under the insulation.

Also what is a good product to use for a vapour barrier?

Thanks

Wookston

 

[noseall]

The vcl will need to be below the insulation i.e. fixed to the underside of the joists prior to fitting plasterboards. Using foil backed plasterboards is a good way of dealing with this.

Your biggest concern is dealing with the venting of the joist roof space. Have you accommodated for this?

 

[jeds]

Vapour barrier always goes to the warm side. Use any 1000g polythene. Seal all joints with aluminium vapour tape. Make sure you seal edges.

One last thing. Why a vapour barrier in a cold deck roof? It won't do any harm but it isn't necessary.

 

[noseall]

Beetcha Jedders!

 

[jeds]

That'l teach me to think and type.