Insulating Sloping Roof
Discussion
I'm looking for some advice at the best way of insulating a sloping ceiling/roof.
Part of one bedroom has a sloping ceiling, it is currently uninsulated. It is the roof outside with only the void between the back of the lath and plaster and the roof tiles about 75mm. Its the width of the room 5m and about 1.2m in length, slope is about 30 degrees. In the loft there is a beam running the width of the house which is about 300mm tall, access is limited to the gap between the rafters and the top of the beam and the ceiling joists and the bottom of the beam (booth about 300x50mm).
So far I'm looking at;
1) Access from outside, tiles off, board insulation 30 or 50mm depth.
2) Access fro bedroom, plaster off, lath off, board insulation 30 or 50mm depth, new plasterboard and plaster, decorate etc.
3) Access from loft, thin rigid or foil/bubble wrap type insulation pushed into gap.
The roof is slate and really needs doing in the next five years but don't currently have the funds, I would be loathe to have to do the bottom 2m or so of the roof. (Not in my DIY skills either) Plastering isn't either and I know it will make a horrendous mess taking the lath off (new baby expected in 5 weeks too). The is no sarking so any spray in type expanding foam or beads would just end up in the street.
It gets very hot in there at the moment, its south facing, the rest of the loft is insulated with glass fibre matting.
Is there anything I've overlooked?
Part of one bedroom has a sloping ceiling, it is currently uninsulated. It is the roof outside with only the void between the back of the lath and plaster and the roof tiles about 75mm. Its the width of the room 5m and about 1.2m in length, slope is about 30 degrees. In the loft there is a beam running the width of the house which is about 300mm tall, access is limited to the gap between the rafters and the top of the beam and the ceiling joists and the bottom of the beam (booth about 300x50mm).
So far I'm looking at;
1) Access from outside, tiles off, board insulation 30 or 50mm depth.
2) Access fro bedroom, plaster off, lath off, board insulation 30 or 50mm depth, new plasterboard and plaster, decorate etc.
3) Access from loft, thin rigid or foil/bubble wrap type insulation pushed into gap.
The roof is slate and really needs doing in the next five years but don't currently have the funds, I would be loathe to have to do the bottom 2m or so of the roof. (Not in my DIY skills either) Plastering isn't either and I know it will make a horrendous mess taking the lath off (new baby expected in 5 weeks too). The is no sarking so any spray in type expanding foam or beads would just end up in the street.
It gets very hot in there at the moment, its south facing, the rest of the loft is insulated with glass fibre matting.
Is there anything I've overlooked?
I'm just about to get a plasterer to do that very job.
He's pulling down lath & plaster, wedging Kingspan board between the rafters and reboarding with foil backed plasterboard. Then it'll be a skim over.
I think that this is the least disruptive way of doing the work. Tiles off would require a lot of scaffold in my case.
Be aware that:
If your house is old enough to have lath and plaster, it probably doesn't have a felt liner behind the tiles. You must leave a 2" gap between the inside of the tile and the insulation for airflow. These roofs were designed to breathe, if you block it up you'll get condensation, damp and rot issues.
You'll need to strip any wallpaper so the plasterer can skim to the walls.
And (in my case) there will be 90 odd years worth of black gunk sitting on the back of the lath. It will come down and ruin any carpets or furniture.
He's pulling down lath & plaster, wedging Kingspan board between the rafters and reboarding with foil backed plasterboard. Then it'll be a skim over.
I think that this is the least disruptive way of doing the work. Tiles off would require a lot of scaffold in my case.
Be aware that:
If your house is old enough to have lath and plaster, it probably doesn't have a felt liner behind the tiles. You must leave a 2" gap between the inside of the tile and the insulation for airflow. These roofs were designed to breathe, if you block it up you'll get condensation, damp and rot issues.
You'll need to strip any wallpaper so the plasterer can skim to the walls.
And (in my case) there will be 90 odd years worth of black gunk sitting on the back of the lath. It will come down and ruin any carpets or furniture.
DrDeAtH said:
Best way would be to strip lathe and plaster off. Infill with 50mm Celotex flush with the inner face of the rafters.
Then overboard with 50mm thermal plasterboard. It will be easier than trying to fix plasterboard through an extra layer of Celotex on the inside face.
Really ?Then overboard with 50mm thermal plasterboard. It will be easier than trying to fix plasterboard through an extra layer of Celotex on the inside face.
I could overboard celotex with plasterboard faster than you could strip, clean up and infill celotex.
If you mean using thermal boards is easier than celotex and plasterboard - of course it is - which is why I mentioned it first - it also costs a lot more.
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