Alexphd1 Posted July 21, 2016 Share Posted July 21, 2016 (edited) I will put my hands up and be honest, i do not have a clue about the make up of the roof. the architect and engineer have asked what do I want. Its a pitched slate/metal roof with a room in loft . We are in Scotland so sarking will be used. Its a ridge beam design with a target u-value 0.1 with emphasis on air tightness. architect has suggested rockwool between and space blanket (?) on top of rafter under sarking which i am not keen on. I was more thinking solid insulation (spec unknown) again on top with rockwall between but how this works with sarking etc i dont know. I have already bought the roofshield membrane. any advice/opinions welcome. cheers. Edited July 21, 2016 by Alexphd1 Link to comment Share on other sites More sharing options...
Ferdinand Posted July 21, 2016 Share Posted July 21, 2016 Rockwool probably good and cheap, if you have enough thickness. Space blanket (=multifoil) is best left to spacemen and mountain rescue people, as being very expensive for the insulation it actually provides. There should be lots about this already here, even though we have just started. Try a search for multifoil. Ferdinand Link to comment Share on other sites More sharing options...
PeterW Posted July 21, 2016 Share Posted July 21, 2016 You can get a pre-insulated rigid sarking board which has PUR insulation already bonded to it - its designed for the situation you describe. What's unclear is why you would do it that way, and not go with sarking > rockwool > PIR insulation from outside to inside as that removes the thermal bridge and also puts the least permeable insulation on the inside as the vapour control membrane. 1 Link to comment Share on other sites More sharing options...
Alexphd1 Posted July 21, 2016 Author Share Posted July 21, 2016 Peter w. So the pir would be between the rafter and plaster board? Where what would the best for air barrier for tightness? Link to comment Share on other sites More sharing options...
PeterW Posted July 21, 2016 Share Posted July 21, 2016 (edited) That's correct - this probably helps a bit more with the make up of the roof. The VCL provides the air tight layer in this model [from http://www.greenspec.co.uk/building-design/unventilated-roof-insulation ] Edited July 21, 2016 by PeterW Added source URL 1 Link to comment Share on other sites More sharing options...
ToughButterCup Posted July 21, 2016 Share Posted July 21, 2016 Idiot roof question. There but for a syllable.... We like all sorts of questions Sorry ...couldn't resist it. Ian Link to comment Share on other sites More sharing options...
Crofter Posted July 23, 2016 Share Posted July 23, 2016 My roof design is exactly as PeterW shows (although with metal sheeting rather than tiles). You could use foil-faced PIR and tape it to create the VCL, but I'm just going to use plastic. Link to comment Share on other sites More sharing options...
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