I am insulating above the ceiling of my back bedroom. The ceiling slopes down and there is only 4 inches between the ceiling plasterboard and the roof felt above. Since I have to leave 2 inches for air flow, this means I can only put in 2 inches (50mm) of insulation so I'm wondering what the best type would be. Any advice welcome. (I have cut a section out of the ceiling so I can put the insulation in.)
Best 50mm insulation material
- Thread starter ZACCCC
- Start date
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Celotex, Kingspan or Xtratherm or any other PIR insulation, they are all much of a muchness.
Forget the foil blankets types they need a bloody great air gap each side to work and are very expensive.
Forget the foil blankets types they need a bloody great air gap each side to work and are very expensive.
If you need really good but thin insulation, one option is an aerogel e.g. Spacetherm. But it is vastly more expensive than PIR or mineral wools. If you said that you had only 20mm then it would be worth considering. With 50mm, you're probably best with something more conventional.
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Yes at £300 odd for 2400x1200x20 that's a real bargain! 
He means under the PB, then you'd have to board under that too.
Not a problem - 2" clearance between the top of the insulation and the felt would be OK.
So it would be a sort of double ceiling with 30-40mm insulation between the two sections of plasterboard? I'm not sure if my DIY skills would be up to that. So the plasterboard nails would have to go through two lots of PB and the insulation into the joists?
I think the OP was hoping to insert the insulation down the gap and leave the PB in-situ, it is possible but fiddly, depending on the set-up, and prone to leaving inaccessible gaps down the sides of the insulation, if the rafters are all over the place its probably a no-goer.
@ the OP I would be using any nails, that'll just shake apart what you've already got. Screws only.
@ the OP I would be using any nails, that'll just shake apart what you've already got. Screws only.
The ceiling is about 8ft x 7ft (the 7ft bit sloping down). I can insulate the first foot or so of the 7ft from the loft but then it becomes inaccessible from the loft so I've cut a foot wide section out of the sloping ceiling going right across the whole 8ft. From here I can push in the insulation down towards the eaves and also up to meet the section I've been able to do from the loft.
Just wondering if my skills are up to putting up another PB ceiling under the existing one.
R
RogueHanger
Take down all the PB on the sloping part.
Insert 50mm insulation between joists.
Then re-board with insulation backed PB (30 or 40mm insulation) and long enough screws to screw into joists. 30mm insulation + 12.5mm PB, use 60-70mm screws.
Use scrim tape along edges. Fill edges and screw heads.
Where new PB meets wall and exisitng ceiling, you'll need to cut it at an angle.
Insert 50mm insulation between joists.
Then re-board with insulation backed PB (30 or 40mm insulation) and long enough screws to screw into joists. 30mm insulation + 12.5mm PB, use 60-70mm screws.
Use scrim tape along edges. Fill edges and screw heads.
Where new PB meets wall and exisitng ceiling, you'll need to cut it at an angle.
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