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Topic starter
Anyone any experience of this? I seem to be reading different opinions online.
Bay window with full lead flat roof. Outside lead work is in good condition.
We're decorating the room which will need skimming, so I'm thinking off dropping ceiling and putting some insulation up there. After poking a hole in the old lath and plaster bay ceiling, it looks like I have around 140mm before the roof deck.
So, I'm thinking of putting 100mm of PIR board between the rafters, vapour barrier and then re-plaster board the ceiling before the plasterer comes to skim.
This would leave a ~40mm air gap to the roof deck but there's no external ventilation in the fascia. Likely to be a problem? Have read some people recommending filling the void completely with insulation and not leaving an air gap given there's no ventilation currently.
Any steers gratefully received...thanks.
Posted : 14/03/2022 6:21 pm
If you fully fill the void with insulation and have an effective vapour barrier below it at ceiling level you have a "warm" roof. If you have a vented void above the insulation you have a "cold" roof (and don't necessarily need the vapour barrier). Either is ok. I would go for warm, but the vapour barrier must be effective (no holes for cables etc), otherwise you will get condensation on the underside of the lead.
Posted : 14/03/2022 6:44 pm
Topic starter
Cheers squirrel, there are no cables etc in the roof space so should be able to warm roof it. I guess butyl tape or something to fix the vapour barrier where the plasterboard will screw through it.
Posted : 14/03/2022 7:31 pm
Yep, or a generous smear of mastic.
Posted : 14/03/2022 7:37 pm
I did fully fill the cavity above on our old one in Sheffield.
Filled it with rigid foam offcuts I had and filled any gap with squirty waterproof foam left over from installing the windows. I then put a thin (20mm foam?) Insulated plasterboard over it all, extended over lintel. When it was skimmed over it looked just as it had been before, just 30mm lower ceiling.
Posted : 14/03/2022 7:55 pm
