Upstairs bay window insulation

[Egg1]

Hello,
Just after some guidance on insulating upstairs bay window.
Have some mould growth so needs sorting.
Cut back some plaster board and it had some very old insulation in.

Am I best filling the void with new loose insulation and then laying some insulated plaster board over the old boards?
If I do use loose insulation will I need a vapour barrier?

See pics

Thanks in advance

 

[catlad]

If it was my house, I would take down all the plasterboard, remove all the old insulation, add new kingspan/cellotex between what was supporting the plasterboard, then add some of the same underneath so you have a nice shiny silver surface, refit foil backed plasterboard and skim.

 

[Egg1]

Was beginning to wonder if it would be easier to get rid of the old plaster board.

Thanks

 

[accelerator]

Here's my take:

Check the roof isn't leaking anywhere.

Remove the old plasterboard.

Cut rigid foam board insulation (PIR) to fit between the rafters. Consider using foil backed boards for extra heat reflection, foil facing down. Close any gaps between insulation and rafter with foil tape.

Reinstall ceiling using foil backed plasterboard, with foil facing down into the room. This will create your vapour barrier.

What I'm not sure about is whether it would be worth adding some sort of waterproofing, like a vapour barrier, above the insulation, so that if the roof started leaking it added additional protection. However, this might also trap moisture and might be a bad idea.

 

[noseall]

Hello,
Just after some guidance on insulating upstairs bay window.
Have some mould growth so needs sorting.
Cut back some plaster board and it had some very old insulation in.

Am I best filling the void with new loose insulation and then laying some insulated plaster board over the old boards?
If I do use loose insulation will I need a vapour barrier?

See pics

Thanks in advance

Like here below. Foil tape the joints on both layers and use foil backed (duplex) plasterboard….

Foil1

• noseall
• 2 Apr 2019

Foil2

• noseall
• 2 Apr 2019

Foil3

• noseall
• 2 Apr 2019

 

[Egg1]

Thanks noseall.