I have a loft conversion with a sloping ceiling up against the rafters.
Going over it with a thermal camera it can see the rafters, and it appears
some of the bays have been 'forgotten' in terms of insulation - on a cold
night and the room heated, with the rest of the walls at 16C, the cold bays
are at 13-14C. Moisture I measure at about 15% all round, so I don't think
it's damp.

It would be good to sort out the cold spots, so I'm wondering how to
insulate:

1. Take off the roof tiles and add insulation from above. That's fairly
drastic and is going to require scaffolding etc. Only worth doing if the
scaff is up for something else

2. Take down the ceiling and add Celotex from below. Still drastic, and I
don't know if there's any asbestos in the (1970s) ceiling.

3. Retrofit insulation panels in front of the ceiling. Due to the height
limitations that probably means aerogel-backed plasterboard. The area isn't
enormous (two patches of 3m x 1m) so it wouldn't be unaffordable to do that,
although it would need reskimming after (the rest of the ceiling is artex).
But what would need to be done in terms of condensation and moisture
prevention? It's a bedroom so it's not really feasible to eliminate the
occupants

4. Treat it like a wall cavity and inject cavity fill (spray foam? beads?).
Is there something that can be used that won't ooze out under the tiles?
How does this work in terms of preventing moisture, especially collecting
near the rafters or running down the inside? Is there a risk of the fill
absorbing water? I'm guessing this isn't DIY-able?

(I also found a 2m x 1m bit of cavity wall that had been 'forgotten' so
that's another job to do)

5. Something else?


Thanks
Theo