Advice on upgrading insulation of vaulted ceiling

[FozzieBear]

I have a vaulted ceiling in two of the bedrooms of my bungalow. When rebuilt in around 2000 the spec was for 125mm rafters and 75mm celotex cut between the rafters with a pvc vapour barrier stapled to the rafters and then overboarded with 12mm plasterboard as below.

I have two aims. Firstly to get rid of the artex and secondly to increase the insulation of the ceiling. Can I attach foam backed plasterboard directly over the exuting plasterboard and skim or should I put 50 x 50mm battens secured to the existing rafters and then cut 50mm celotex between them with a new 12.5mm plasterboard and skim ceiling. with the existing vapour barrier in place is this trapping moisture in the new battens and insulation? Alternatively do I need to remove the existing plasterboard and vapour barrier and plant battens directly on the rafters and then add additional insulation? Any advice would be appreciated.

 

[noseall]

I have a vaulted ceiling in two of the bedrooms of my bungalow. When rebuilt in around 2000 the spec was for 125mm rafters and 75mm celotex cut between the rafters with a pvc vapour barrier stapled to the rafters and then overboarded with 12mm plasterboard as below.
View attachment 369370 View attachment 369369

I have two aims. Firstly to get rid of the artex and secondly to increase the insulation of the ceiling. Can I attach foam backed plasterboard directly over the exuting plasterboard and skim or should I put 50 x 50mm battens secured to the existing rafters and then cut 50mm celotex between them with a new 12.5mm plasterboard and skim ceiling. with the existing vapour barrier in place is this trapping moisture in the new battens and insulation? Alternatively do I need to remove the existing plasterboard and vapour barrier and plant battens directly on the rafters and then add additional insulation? Any advice would be appreciated.

Add more underneath. No need for battens. We do it a separates rather than inso' backed boards. Much easier and you can stagger the joins and foil tape the joints and use Duplex boards.

 

[FozzieBear]

Add more underneath. No need for battens. We do it a separates rather than inso' backed boards. Much easier and you can stagger the joins and foil tape the joints and use Duplex boards.

Thanks @noseall . What do you mean by separates rather than inso" backed boards?

I assume you mean Gyproc Duplex which has foil backing but where does the extra insulation figure?
Many thanks

 

[noseall]

Thanks @noseall . What do you mean by separates rather than inso" backed boards?

I assume you mean Gyproc Duplex which has foil backing but where does the extra insulation figure?
Many thanks

Separates as in sheets of foil PIR insulation and sheets of foil backed plasterboard - rather than insulated plasterboard. I hate the stuff.

 

[FozzieBear]

Ahh so you would mechanically fix or glue the insulation first then overboard with Duplex using long screws through both?

 

[mikeey84]

I find it easiest to stick a couple of screws through the insulation (at an angle to stop them pulling through) so it stays up

 

[Ivor Windybottom]

Get the proper washers, don't put screws in at an angle!

Buy TIMco MID36SS Stainless Steel Metal Insulation Disc Washers 36mm

Large diameter disc insulation washers, for use with screws to hold insulation materials to battens. They can also be used for cracked ceiling repairs. These insulation washers have a 5.5mm diameter hole in the centre. They do not come supplied with screws, meaning you can use the desired length...

www.tcfixings.co.uk

 

[mikeey84]

Think the washers are overkill if you are overboarding within the next 10min myself

 

[noseall]

Ahh so you would mechanically fix or glue the insulation first then overboard with Duplex using long screws through both?

Correct. You don't even need to line the insulation sheet edges up with the rafters either. But it is wise to stagger the joints with the plasterboard.

 

[FozzieBear]

One last question. How do you professionals deal with the joint between wall and ceiling when overboarding. do you:
1) Cut boards as close to wall as possible and justs skim, telling housholder to get decorator to caulk corner with decorators caulk?
2) Tape edges, skim and cut off surplus from wall and brush in?
3) Leave a slightly larger gap and fill with bonding prior to skimming?
Many thanks