Advise on best way to insulate dormer flat roof

[Steveshouse]

Hi
Recently moved into a 1960s build Dormer bungalow and the plasterboard was shot on the dormer flat part of the roof, so I set about replacing it.

When I removed the wrecked board it was apparent there was no insulation above - but if you look up the rafters on the main pitched part of the roof, there is wool type insulation below tiles and above the rafters with brown paper underneath it.

All the main roof is like this and I assume this is a warm roof even though the insulation is about 20mm thick.

My question is can I insulate the flat roof between the rafters and plasterboard without causing any problems with the rest of the roof? If so, what would be the best approach?

Also, am I storing up any problems by leaving my roof open like this until I fix it.

Your help would be much appreciated.

Thanks
Steve

 

[catlad]

You can put kingspan/celotex between and insulated plaster board to finish.

 

[Steveshouse]

Hi catlad

Thanks for your reply, would the insulated pb cost me headroom?

Steve

 

[catlad]

37.5mm is the thinnest and upwards it will help eliminate cold bridging.

 

[Steveshouse]

Hi and thanks

Is this a Kingspan product and will this sit up against the Kingspan insulation or does it need an air gap - will it have a vapour barrier?

I am also looking to overboard the rest of the dormer which is covered with woodchip wallpaper with foil back pb - would you say this is ok to do?

thank you

 

[catlad]

Yes it has a vapour barrier and yes you can overboard no air gaps on the warm side, celotex pl4000 is an alternative to kingspan.

 

[Steveshouse]

Thanks catlad

Did you understand my situation with the roof insulation? Insulated above the rafters.
Am I ok leaving this ceiling open whilst I fix it?


cheers

Steve