I've got an 8yr old extension on my house. Last year I had a thermal imaging survey and they identified lots of cold spots on the plasterboard. They say the most common cause for this is that the board has not been glued around the perimeter and then cold air comes down from the loft above and chills the whole wall - nice!

So the proposed solutions are crawl around the loft (right in the eaves - cosy) and seal the top of the plasterboard. Not sure with what, squirty foam maybe.
The other option is to cut a strip around the top of the plasterboard and pack with plaster.

I'm not really that keen to get into these eaves. I'm also not super excited about cutting out all that plasterboard but with a good vac maybe it will be OK?

What do people think about this? The loft access is really tight as it is right in the corner and there is a room in that part of the loft as well. Also would need to remove all the insulation so I can see where to stand, or rather lay down.

If I cut the plasterboard what would be a good tool to use to do this? Dremel?

Are either of these potential solutions actually any good?

This sounds familiar. Cold air from the loft is passed on the way down by lots of heated air from the home, taking with it moisture potentially to condense when it hits the cold loft. my HS has the same feature. The loft insulation was mouldy around the eaves

I dragged the insulation back from the eaves, got a vac in there and really cleaned up the top of plasterboard and wall plate. Than taped from wallplate to plasterboard to make a good airtight seal. Then purged with FM330 foam from below up against the tape. Then installed kingspan kooltherm across the area for good measure. My BCB said he could see I was going a better job than a tradesman

Thanks all,
I think I will do the drill and squirt technique initially and then when I'm feeling like being in a small dark space I'll check things out from above!

When using drill and foam fill. Cut a series of tight fitting plugs before you start drive them in immediately after filling a hole, it will save an awful amount of mess

Posted By: philedgeId definitely test the spread of the foam within a gap of the size you have

yeah makes sense to do a few tests before getting under way. I've got about 20m to do so will keep me out of trouble for some time!

Posted By: tychwarelCut a series of tight fitting plugs before you start drive them in immediately after filling a hole

plugs are a good idea! I've got some dowel, probably a bit bigger than the holes I was planning on drilling but would make easy plugs - what did you use?

Thx again one we did earlier https://readinguk.org/draughtbusters/going-further/dot-and-dab/

Please review pics

Thanks for all the suggestions. I ended up crawling around up there on Boxing Day as I had nothing to do.
It wasn't as bad as I had expected although I'd probably not do it again as a fun day out. Some of these gaps took a lot of squirty foam!

I noticed that the cavity was insulated (phew) and also that the insulation just sort of ends. Should the cavity be sealed somehow? Also is it really necessary to tape over the joints?

I also realised that all the downlights are probably a problem, is there some way to seal these as well?

Going to try and post a picture of the cavity...

Id do the following to achieve what Tony has suggested. Raise the cavity insulation level with the wooden wall plate using loose fill or cut slivers of loft roll. Then lay loft roll the thickness of the truss ceiling joists over the top of the cavity and out into the loft. Add as much insulation as you want over the top of this first layer running at 90 degrees to keep the ceiling joists nice and warm with no air gaps over the top of the ceiling joists. Where the inslulation butts against the under side of the felt youll need to cut it at an angle to give a 10-20mm continuous gap for ventilation. You can fit plastic or thin ply under the felt to maintain this gap if you dont want to cut the insulation but I find cutting the insulation a better job as youre not tempted to squash the insulation under the plastic/ply

Before you start make yourself a smooth board to lie on that you can slide around on easily. Get a decent head torch too

get a blower test at some point to find where you miss. Well worth the expense.

Well done, you must have a decent pitch on your roof too get into the eaves that far?

In my house, removing the bottom course of tiles is the only option. I tried filling from above with some aquarium tubing attached to the foam gun, because there's no vertical space for a foam gun on its own, but the coverage must have been pretty spotty.