Cold Bedroom Mystery

[AlwaysLearning]

I'm absolutely out of ideas to solve this mystery ...

 

W facing first floor bedroom is always colder in winter and hotter in summer. Approx 3m x 3m. S wall is an uninsulated party wall with nextdoor. But our bedroom on the E side that shares the party wall doesn't have heat problems. W wall was cavity insulated with blown mineral wool back in the 80s. W wall has a large DG window with no noticeable draughts. N wall is shared with another bedroom which doesn't have a temperature problem either. Room heated with a hot water rad with TRV. When the heating is running, the room is comfortable. Heating off, and the temp drops. Ceiling to the attic, 270mm insulation. Wooden floor with 170mm mineral wool insulation in the void and fully carpeted. One door and no noticeable draught under it.

 

I've sealed the ends of the joists that sit in the party wall incase there's air movement there. I've sealed electrical sockets and the cable entry to the ceiling rose. I've sealed floor/skirting too.

 

I'm out of easy ideas of where the heat is going or coming from. I'm grasping at: having the party cavity wall insulated though I've yet to find a local installer who'll touch party walls. Perhaps the 80s insulation wasn't done properly or has settled though the rest of the house is ok. DG units have utterly failed with whatever gas was used in the 2000 has leaked away but no condensation is in the gaps. Though all the other DG windows are ok.

 

Or am I missing something really obvious? Is there an experiment I can do to rule in or out some factor?

[Radian]

If you had said the room was colder in both winter and summer I would suspect the CWI being saturated through some fault in the exterior masonry or roof but your symptoms suggest a lack of CWI in that wall. I don't suppose you've got access to a thermal camera? If the CWI has gapped at the top of the wall, the heat collecting at ceiling level would have an easier time getting out. A few small drill holes and cheap usb inspection camera could find out.

[AlwaysLearning]

Cool in winter, hot in summer. No obvious cracks or damp patches in the external wall which led me to clutch at symptomless DG failure.

 

I did try a cheap plug on thermal camera last year, but the quality of the image was so pants as to be near useless. Seriously tempted to buy a better one for my toy box though.