What's The Right Way To Finish Ceiling Edges?

[MrMiller]

Hi Folks

I've just about removed all my tiles and backer board from our bathroom.

The corners around the ceiling look like this:-

So that's just a pretty thin layer of lath and plaster there at the moment, with the freezing cold attic above it. I'm planning to get thick insulated backer boards for the wall but that's still going to leave a gap against the edges there for heat to potentially escape through.

So what's the preferred method to fill that gap below the lath and plaster slats? Should I fill with some kind of expanding foam or filler before securing the boards to the wall?

 

[Dereekoo]

Why is there going to be a gap, boards pushed up tight to ceiling?

 

[robinbanks]

So that's just a pretty thin layer of lath and plaster there at the moment, with the freezing cold attic above it

Found the problem

Insulate the ceiling

Fun/poking aside, the holes at edges are the least of your worries. Thin lath and plaster has nearly no insulating value. If that is all there is between your heated space and the outside world temp of the attic, you should really be looking to put 270mm of wool or 140mm of kingspan up there; your entire ceiling will just soak the room heat up and discharge it to the world, even if you fill the gaps

For the gaps, per Derekoo they won't be gaps if the wall boards touch the ceiling but expanding foam can be used to fill the gaps if you like

 

[MrMiller]

Why is there going to be a gap, boards pushed up tight to ceiling?

Yeah, there isn't going to be a "gap" gap as such. I was just meaning at the corners there, there will be airflow around where the ceiling plasterboard is.

Maybe its not an issue but its just that the bathroom was quite a cold room before and I'm looking at going with some more expensive, wider 50mm insulated backer boards, so I just want to make sure I'm maximising the insulated level all round.

 

[MrMiller]

Found the problem

Insulate the ceiling

Fun/poking aside, the holes at edges are the least of your worries. Thin lath and plaster has nearly no insulating value. If that is all there is between your heated space and the outside world temp of the attic, you should really be looking to put 270mm of wool or 140mm of kingspan up there; your entire ceiling will just soak the room heat up and discharge it to the world, even if you fill the gaps

For the gaps, per Derekoo they won't be gaps if the wall boards touch the ceiling but expanding foam can be used to fill the gaps if you like

Thanks - there is plenty of knauf rolled wool stuff up there actually, so maybe it will be okay...

 

[robinbanks]

If the area above is covered with wool and not accessible to world air I wouldn't worry about it, but feel free to fill with expanding foam

 

[MrMiller]

If the area above is covered with wool and not accessible to world air I wouldn't worry about it, but feel free to fill with expanding foam

Thanks - Probably just leave it then. If I can avoid using expanding foam that would be my preference!