Insulating curved timber frame bay in 1935 art deco house

[ap2048]

I would like to insulate the wooden frame bay on the 1st floor of my house which sits above double glazed windows on the ground floor (green arrow)

I have looked at options used on previous posts about this and most suggest using celotex but I have a few concerns about this:

1) Risk of an incomplete vapour barrier causing condensation. The curved nature of the bay increases the risk of gaps and therefore condensation. I also don't want to reveal the full length of the timber frame due to extent of work and disruption, instead pushing celotex from top into studs below floor boards and into bottom of frame above ground floor windows. But this means I cannot put a vapour barrier at the base or fill gaps with filing foam hence my concern about condensation.

2) It will be more tricky to fit celotex in curved section although not impossible. Also harder to fit curved plasterboard over the top although again I know you can bend plaster board.

3) There is a corner at one end adjacent to a wardrobe which will make access for that part more difficult (see images).

I have recently insulated the ceiling so am waiting to see the effect this has on warmth and condensation. It could be that having insulated the ceiling that that is enough but if not, I wonder what people's thoughts are for using celotex or perhaps suggest another insulation. A friend suggested vermiculite as it would be easier to install given curve and also less prone to condensation but I am concerned about thermal performance. It would however be a much simpler method and would maintain the current curve.

Thanks and suggestion and thoughts very welcome. I am happy to consider all types of insulation vs ease of installation vs thermal performance. Cost not an issue

 

[ree]

OP,
Why not post pics showing the bay frontage, & the bay roof?

 

[Deluks]

1) from your description, sounds like you will struggle to achieve full coverage and may end up with cold spots.
2) you can score the back of the boards to make it 'bend' into the space. Not ideal as you will have cold spots where the cuts are.
3) Close that gap off, fill it with insulation, cap it off with a bit of painted MDF/window board.

The ceiling having been insulated will probably increase the likelihood of condensation on the wall section.
You might find that theres already something in there, might just be 2" of sagging fibreglass insulation or something equally retro.

The fact that it's curved, means that wool slabs will be the easiest to install.
Something like Dritherm 32 in the void, go over it with a thin insulated plasterboard to cover the studs.
Don't not cover the studs unless you like zebra's.

 

[ap2048]

OP,
Why not post pics showing the bay frontage, & the bay roof?

Thank you. I have added pictures of the bay roof before and after adding attic insulation which in itself seems to be making a difference. I'll add a picture of the bay front this morning.

 

[ap2048]

1) from your description, sounds like you will struggle to achieve full coverage and may end up with cold spots.
2) you can score the back of the boards to make it 'bend' into the space. Not ideal as you will have cold spots where the cuts are.
3) Close that gap off, fill it with insulation, cap it off with a bit of painted MDF/window board.

The ceiling having been insulated will probably increase the likelihood of condensation on the wall section.
You might find that theres already something in there, might just be 2" of sagging fibreglass insulation or something equally retro.

The fact that it's curved, means that wool slabs will be the easiest to install.
Something like Dritherm 32 in the void, go over it with a thin insulated plasterboard to cover the studs.
Don't not cover the studs unless you like zebra's.

Thank you ok yes this makes sense and a better option then celotex due to less risk of cold bridging. What about vermiculite? That would be easier to install as I wouldn't have to rip out the current plaster board completely.