Timber frame wall insulation

[daggermark]

I've had to remove some damaged sections of plasterboard on external wall of a bedroom. The house is timber-framed, so even the external walls are studwork on the inner leaf.

Behind the plasterboard I've found fibreglass insulation between the studs. It is pretty lacking in many places - it doesn't fit snugly to the studs and is pretty thin in places.

What is my best bet for making this good before I re-board? The cavity is only 89mm deep, and all the fibreglass rolls I've seen seem to be 100mm thickness or more. Would it be better to use 75mm insulation board? Would this create a problem as it would differ from the rest of the insulation and create warm/cold spots?

 

[freddiemercurystwin]

100 will squash to 89.

 

[daggermark]

Fair enough. Most of the fibreglass seems to be sold as 'loft insulation' but can I assume it is the same stuff?

 

[TimboTwo]

Rockwool is better for you.

 

[Deleted member 174758]

Rockwool, Earthwool, mineral wool are basically all the same thing. Mineral wool is far better than fibreglass or PIR insulation (e.g. Cellotex, Kingspan, etc) for sound insulation. The modern versions are treated with something to reduce the irritant effect of the dust on the respiratory tract, but you do need to wear a mask and ideally gloves when handling this stuff as all of them produce irritant dust when being cut. Fibreglass is also a skin irritant (cured by taking a hot shower or bath)

 

[daggermark]

I've just discovered Knauf and Rockwool both make a specific 'timber framed wall insulation', which both seem to cost an arm and a leg. I can't get my head around why, the stuff they sell for lofts is also A1 fire rated and has a similar R value. Perhaps it is the sound insulation performance.

 

[Deleted member 174758]

Mineral wool batting or slab is more rigid and is easier to install (for that reason) than material on roll. Maybe that's the reason.

As it happens mineral wool is naturally fire retardant, better than fibre glass and far better than PIR insulations, but there are also special fire rated versions for use in fire stopping work which have white intumescent coating on both faces as well as embedded "chicken wire" for strength. Typical uses include for fire stopping holes around services such as electric cabling , gas pipes, etc where they go between fire compartments, e.g. where they run between two floors in a block of flats or a hotel and the like

Edit: @daggermark I have added a couple of afterthoughts to what I originally wrote

 

[daggermark]

The knauf gear for timber framed walls is called 'frametherm' and is actually on a roll too. The lowest grade one, 'frametherm 40' has identical thermal properties to the bog standard knauf 100mm loft roll but they claim only the frametherm offers acoustic insulation as well as thermal. It looks identical in the photos!

 

[JohnD]

But it may be heavier.

 

[daggermark]

I think I've found the answer. Knauf say that 'omnifit' can be used for my application and it seems easier to get hold of, nowhere seems to stock the frametherm. Thanks everyone for the help.