_Matt_ said:
I have built lots of outdoor buildings...converted garages etc. and never worried about an air gap...I usually fill the cavity with PIR and then line with standard plasterboard...if there is no air, there is no mould and have been doing what I do for 30+ years...I still go back to properties where I have done this and 10 years later, no problems
The more you seal up a bulding, the more issues you will have though...UPVC adds lots of issues...as does cold hard surfaces..i.e tiles etc...for these situations you really need full heating and not just convection rads...
If not sealing up the entire building the air gap in the roof wont matter...30mm PIR isnt worth the investment as its not really efficient...I use 50-75mm on pitched roofs...100mm on flat roofs and 75mm on walls (made from tanalised 3x2) again no air gap...ventilation then becomes important (doors and windows act as ventilation too) and as long as you have an exchange of air daily...all good...a ceiling fan on constant or extractor & vent at opposite ends would work if not in daily use although I expect it might be
By all means clad the out side but first line it...12mm plywood best...OSB good enough...then a breathable membrane, then the cladding...also screw cladding at 300mm intervals, stops it warping along its length...which it will try to do
Inside standard 12.5mm plasterboard walls, 9mm on
the roof...quick qkim of plaster as opposed to tape & fill as it
protects the plasterboard a bit more from accidental damage and adds
another layer...which is better for paint finish than just plasterboard
alon
Lasty get timber from a timber yard, same as recommendation for PIR from a builders merchant...Selco often has offers on PIR or Feebay is good for it too...over orders
