I am starting the renovation of a late '60's bungalow, cavity walls, brick outer with (what looks like) cinder block inner leaf, 50mm cavity (empty)

So far I have changed my mind numerous times with regard to method of insulating the cavity walls, until yesterday it was going to be blow in EPS beads, today it may be kooltherm k118 screwed to 50x25mm battens backed with dpc.

Has anyone here knowledge (has actually used) this kooltherm board? 

When reading IWI matters, the vapour barrier issue appears to be somewhat manic, so when reading about the kooltherm application it seems simplistic in comparison.

Can someone shine a light into my darkness on this????? 

 

I have not used K118 but I have used Gyproc Thermaline Super, which is a phenolic board bonded to foil-backed phenolic insulation similar to K118.

 

If, like the Gyproc board, the Kooltherm K118 has foil on both sides (as I am sure it does, otherwise it would be banana-shaped) then you could argue that it has a VCL on the warm side. But when you put 2 boards together where is the VCL? For this reason when I was using petrochemical boards I preferred to do a lime parge coat on the wall, approx 6mm min thickness, then use the 'raw' boards, taping all the joints and perimeters (I used hi-spec air (and vapour-) tightness tape, not cheap foil tape. Then battens then plasterboard. I would go with what you describe as 'manic'. You cannot have too much attention to VCL tightness. Note I used battens on the warm side, not the cold side.

Beads in the cavity. 

 

Parge to the wall. 

 

Battens/internal studwall with mineral wool infill. 

 

Kooltherm in the Bin. 

Thanks for replies.

Have made decision - Beads into the cavity, no further additions (insulation), reason being this is the original part of the dwelling and will be bedrooms, bathroom and utility. The actual living area will be the extension and therefore up to current spec.