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Housing - Renovation: Warm roof as insulation barrier

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  1.  
    • CommentAuthortony
    • CommentTimeOct 23rd 2012
     
    Could my friends do a warm roof right over their difficult to insulate chalet style bungalow, extending the eaves and verges to take EWI at a later date.

    they suggested 200mm pir foil faced insulation, counter batten, retile.

    I was thinking 100mm batts between rafters and 100 sheets over the rafters? join up everything and ensure all is air tight.

    Planning was happy about ridge increasing height slightly

    What do we think about this plan?
  2.  
    We have done this roof on one of our buildings. 100mm between and 100mm over rafters. One minor problem in that planed softwood rafters (we constructed a cut roof with oak purlins) were actually about 94/95mm deep not the 100 as expected, resulting in boards protruding slightly below the underside of the rafters.
    Hoping this will not cause problems when plasterboarding the ceiling - maybe use longer screws and drive home carefully! (have not done the inside of the building yet).
    • CommentAuthortony
    • CommentTimeOct 23rd 2012
     
    Thanks, think their rafters are fully 4" deep
  4.  
    Hi tony, we tend to plywood the roof first and then insulate over the plywood for airtightness and safety.
    • CommentAuthortony
    • CommentTimeOct 24th 2012 edited
     
    Do you do 200mm of insulation over that? how do you fix the counterbattens? Thin ply?
    • CommentAuthorDarylP
    • CommentTimeOct 24th 2012
     
    We have 200mm PIR over 15mm OSB, the PIR is spray glued down to the OSB, the battens are then heli-screwed through the PIR, through the OSB and into the rafters underneath.
    Counter-battens are then screwed to the battens as per normal.

    We are confident this will manage to cope with expected wind and snow loads.

    Cheers:smile:
    • CommentAuthortony
    • CommentTimeOct 24th 2012
     
    What is the roof pitch?
  8.  
    Could you do the 100mm between the rafters and still do the plywood (as VH) with 100mm over that?

    We used "inskew" helical nails to fix through the counterbattens, insulation, and into the rafters. I think we have discussed them on here before. Not sure what length they are available up to.
  9.  
    Maybe depends how much of an eaves overhang you/they want?
    If more is better for future proofing (EWI) then might as well go for 200 over the lot to have a bigger overhang.

    Our roof pitch was only about 30 degrees.

    Like the first roof but with 100mm between and over:

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