Loft insulation

[jackg]

This is for a single storey extension which has a pitched roof with trusses at 4000cts.
So it will require 100mm between the bottom chords and 200mm on top of them.
The height of the loft space will be approx 1.5m with Queen post trusses. When 200mm is subtracted from 1500mm the effective height is 1300mm. So not very high.
I need loft insulation on top of the plasterboard. 52 m sq.
Knauf loft roll 44 and Rockwool are two main products.
The Knauf seems to be cheaper by some margin than Rockwool which does not seem to be so widely stocked as the Knauf.

Is there any particular difference between the two to merit the difference?

Are there any other products worth considering?

 

[mointainwalker]

The insulation value of the two is the same. The Knauf material is much more agreeable to handle than the old yellow fibre-wool, however I have never used Rockwool and cannot say anything on that count. The roll material will need fixing in place somehow before fixing the plasterboard. You will also require a vapour-barrier between the plaster-board and the insulation: this can be the kraft paper backing on the insulation, however I always prefer to use a thin plastic decorator's sheet as it's a PITA messing around trying to tack the paper onto the rafters.

Instead of roll, you can use the same material in batts, which is the same stuff with a small amount of added glue to make them more rigid and easier to fit/hold in place. They are cut into rectangles and cost a lot more per m2.

 

[jackg]

Thank you for your post.
The drawing calls for foil backed plasterboard on the ceiling, which is the same as the vapour barrier you suggest?
I had a vapour barrier roll for the floor which I did not use, maybe I could use that?
My understanding is that the PB is fitted first then the wool?
A screeder suggested using batts as they offer noise reduction as well as insulation, but I can't see how to justify the cost difference?

 

[mointainwalker]

Thank you for your post.
The drawing calls for foil backed plasterboard on the ceiling, which is the same as the vapour barrier you suggest?
?

Foil acts as a barrier, although you should use aluminium tape on the joints for perfection.

Thank you for your post.

My understanding is that the PB is fitted first then the wool?
A?

I think I must be misunderstanding you. You want to fit the wool between the rafters and then your foil-backed plasterboard.

[QUOTE="
A screeder suggested using batts as they offer noise reduction as well as insulation, but I can't see how to justify the cost difference?[/QUOTE]

Batts do offer a little more mass and thus a little more noise reduction, but not much. When I was insulating my internal walls for noise, I compressed 100 mm of fibreglass into 50 mm space. This wasn't very easy, but worthwhile both for effect and cost-saving.

 

[jackg]

Not between the rafters, bottom chords or joists. cold roof.

 

[JohnD]

Knauf loft roll

Knauf mineral wool is now treated with Ecose which makes it softer to handle and it does not shed irritating dust and fibres. It is also sold under other names as an own brand, but you will usually notice that it is brown and "Ecose" is on the wrapper.

I would never use yellow fibreglass again.

 

[Ian H]

Why are you boarding the loft ceiling? Seems pointless with the 1.3mtr height.

 

[jackg]

I'm not, apart for access to CWT etc.

 

[Ian H]

Right, sorry I was reading it wrong.

I would plasterboard first, then lay the insulation ontop. Assuming you have access.