Insulation to fit between 3x2" battens

[markwm]

Is 50mm slab insulation(rockwool) ok to fit in between 3x2" stud wall, built in front of an external wall, or would 100mm be better, compacted in.

I can only find 50mm and 100mm sold locally. Not 75mm(3")

 

[PrenticeBoyofDerry]

Rock wool comes in varrying thickness 50, 65, 80, 90, 100mm and up.
You need a full a fill as possible, have you considered.
What area do you live in?
http://bmdinsulation.com/rockwoolinfo.htm

 

[ajrobb]

Is 50mm slab insulation(rockwool) ok to fit in between 3x2" stud wall, built in front of an external wall, or would 100mm be better, compacted in.

I can only find 50mm and 100mm sold locally. Not 75mm(3")

Don't compact mineral wool insulation as it loses much of its insulation. I'm confused about the type of wall you are talking about.

 

[markwm]

Just dry lining an external wall of a solid(non cavity) wall, bedroom, Basically, building a stud wall in front of it.

Can't I just use loft insulation? It's much cheaper

 

[jono_h]

Insulation works because it is full of air which 'traps' the heat. If you squash thicker insulation into your gap you'll squeeze out the air reducing the effectiveness.
Use something that is 50mm thick, rockwool is Ok, celotex is better.
Or use deeper studs and thicker insulation.

 

[ajrobb]

Just dry lining an external wall of a solid(non cavity) wall, bedroom, Basically, building a stud wall in front of it.

Can't I just use loft insulation? It's much cheaper

Yes, of course you can use mineral wool but I think you must either use rigid batts or fix loft insulation blanket at the top to stop it collapsing into the bottom of the cavity. Your Building Engineer or Building Inspector might require a vented cavity adjacent to the brick.

Have a look at http://www.proctorgroup.com/index.asp?lm=27 to see some ways of using mineral wool to insulate solid walls.

Personally, if I had to live with it:

• strip plaster from the brick
  seal the brick inner surface with a concrete render (e.g. Soundcoat)
  50mm treated battens at 600mm centres
  50mm Celotex on top of the battens (taped joints)
  19mm wood strips (holding Celotex in place and providing service void)
  plasterboard

That gives a U value of about 0.27.

 

[markwm]

Bought some 65mm ROCKWOOL cavity insulation. Hopefully should be good. About £100 for 22sq metres