Bay window PIR insulation plan

[Vector771]

We’ve just pulled off the lining paper under the bay window (1st floor) in our bedroom to discover a huge amount of black mould. The wall under the bay is plastered over brick. I’ve chipped some of this away where the mould was particularly bad and it’s nice and dry behind, so I’m confident this was a condensation issue on a cold wall. The outside face is stone (presumably cladding straight onto brick?).

I’ve had a read through lots of threads about insulating a bay window and have come up with the plan below using the warm batten method. Any feedback gratefully received!

A couple of questions are on my mind:

• Is Wall-50mm Celotex-vapour barrier-battens/25mm cellotex-plasterboard the correct order?
• Am I right to remove plaster to put PIR against brick, and do I need to adhere the first layer of PIR to the bricks or is securing it with battens enough?
• I can't see any fixings on the current window board (which will end up too shallow). Is it likely to be glued on?
• Should I be doing walls in bay to the side of the windows as well as underneath? I'd expect to just leave plasterboard flush where the bay meets the main wall of the room and extend window board round the whole bay, but I guess that would just leave side walls as the new cold spots?

The plan

1) Remove skirting boards and remove plaster back to brick (plaster is in good condition but I’m assuming much more efficient to use those 15-20mm for insulation rather than plaster?)

2) Install 50mm Celotex insulation (including on wall in void below floorboards), foil side against brick. Planning to use Soudal PU adhesive, just enough to hold board in place before battens.

• We’ve been given a lot of 50mm offcuts by neigbours– any downsides to using multiple pieces rather than large sheets?

3) PU foam around any joins/gaps, then tape all seams and add vapour barrier e.g. https://www.wickes.co.uk/Wickes-Gre...FYK-J7r90unQN3jXQR0aAnevEALw_wcB&gclsrc=aw.ds. I understand this isn’t strictly necessary given the foil backing on the PIR but keen to be thorough!

3) Add 25mm battens top & bottom then vertical at 600mm spacing– drill through cellotex into brick to mount battens with 120mm screws in plugs (giving 45mm screw in brick)

4) Add 25mm celotex between the battens (no air gap). Does this need adhesive, or just cut so that it's a snug fit in the frame?

5) Install standard plasterboard

 

[cdbe]

Just foam the whole lot on. Battens not necessary.You can get pvc over capping to extend the window board - stick on with your choice of "no nails".

 

[Vector771]

Just foam the whole lot on. Battens not necessary.You can get pvc over capping to extend the window board - stick on with your choice of "no nails".

Thanks! Is the foam strong enough to hold the plasterboard on? I've never used it!

Good to know about the overboard. I was hoping to replace with a nicer wooden board provided I can get the existing one off...

 

[cdbe]

Yes, the foam (the correct adhesive foam rather than expanding foam - and follow the waiting times exactly) will stick PIR to wall and plasterboard to PIR. The board is probably just stuck on with silicone or no nails but can be cut away with a multi tool if it's stubborn.

 

[Vector771]

Yes, the foam (the correct adhesive foam rather than expanding foam - and follow the waiting times exactly) will stick PIR to wall and plasterboard to PIR. The board is probably just stuck on with silicone or no nails but can be cut away with a multi tool if it's stubborn.

Great, thanks! I don't think the current stuff is plasterboard - it's pink all the way through and has a stoney texture where I've chipped some off and looks pretty well adhered to the bricks in behind!

 

[noseall]

The plan

1) Remove skirting boards and remove plaster back to brick (plaster is in good condition but I’m assuming much more efficient to use those 15-20mm for insulation rather than plaster?)

2) Install 50mm Celotex insulation (including on wall in void below floorboards), foil side against brick. Planning to use Soudal PU adhesive, just enough to hold board in place before battens.

• We’ve been given a lot of 50mm offcuts by neigbours– any downsides to using multiple pieces rather than large sheets?

3) PU foam around any joins/gaps, then tape all seams and add vapour barrier e.g. https://www.wickes.co.uk/Wickes-Gre...FYK-J7r90unQN3jXQR0aAnevEALw_wcB&gclsrc=aw.ds. I understand this isn’t strictly necessary given the foil backing on the PIR but keen to be thorough!

3) Add 25mm battens top & bottom then vertical at 600mm spacing– drill through cellotex into brick to mount battens with 120mm screws in plugs (giving 45mm screw in brick)

4) Add 25mm celotex between the battens (no air gap). Does this need adhesive, or just cut so that it's a snug fit in the frame?

5) Install standard plasterboard

20160107_085741 (3)

• noseall
• 24 Apr 2016

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• noseall
• 24 Apr 2016

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• 24 Apr 2016

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• 24 Apr 2016

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• noseall
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[Vector771]

Photos

Cheers, I'd seen that thread and that was basically what I pulled my plan together on - I was just unsure whether the timber framing was necessary if it didn't already exist and whether I should be removing the plaster or leaving it.