hello again,
Cheers Sean, will take a look. My understanding of multifoils is that they are not all they're cracked up to be but that opinion could be wrong!
- thats my understanding to,
tri-iso super 9, claimed to be equivalent of 200mm fibreglass may only be as effective as 75mm -
www.planningportal.gov.uk/uploads/br/multi-foil-insulation_july2005.pdfgiven that it requires a 25mm gap on both sides it is really 75mm thick,
at around £11 per m2 it may be a bit dear
using render will reduce the 200mm wall u-value from 0.144 to 0.151, effect of any 'insulating' render is insignificant
substituting PIR at lambda 0.022 gives U=0.136 from 0.151
I understand that 89mm timber frames are structurally adequate, 140mm was largely introduced to accomodate extra insulation!
reducing the frame to 89mm but leaving 200mm of PIR gives U=0.122
my concern with rigid insulation is fitting into the timber frame in an airtight manner, perhaps consider a sprayed polyurethane like Walltite from BASF