Increase depth of rafters

Discussion in 'Builders' Talk' started by johnny the m, Jan 4, 2010.

  1. johnny the m

    johnny the m New Member

    Circa 1900 stone and slated mid terraced 2 storey cottage.
    I want to insulate between rafters in loft to use it for storage. No roofing felt exists. Not a lot of headroom - you have to duck even directly below ridge line. Rafters are 83mm deep x 63mm wide at 425mm centres. I want to insulate with 50mm Celotex or similar then plasterbd/skim over. Advised I need 50mm air gap for ventilation therefore need to increase depth of rafter by min. 17mm. Can you tell me if slaters battens come in 63x19mm or would you not bother increasing depth of rafters and make do with 33mm air gap as no felt exists so fairly well vented and further loss of headroom. Phew. Thanks for reading.John
     
  2. wuddy

    wuddy Member

    your airgap only needs to be 25mm but you will also need to vent the top of the roof
     
  3. Willy Duwitt

    Willy Duwitt New Member

    Would another option not be to put, say, 35mm sheets between the rafters and then fixing 12mm sheets under the rafters before fixing your 12.5mm p/boards? This would also reduce cold bridging at the rafters.

    I've found these guys to be very reasonably priced and reliable :

    http://www.builditshop.co.uk/

    When I've ordered, the stuff usually, not always, comes from Travis Perkins

    Hope that helps
     
  4. hallbeck

    hallbeck New Member

    First the bad news - this requires building reg approval, and you are going to need 125mm of celotex, not just 50mm.

    The good news is that ventilating the gap above the celotex is not neccessary - slates are a draughty roofing materila nad there will be loads of ventilation between the slates themselves.
     
  5. mightyapu

    mightyapu New Member

    Why not use a super quilt insulat such as Tri Iso or Thinsulex? Simpler to install and arguably as a good a performer as 125mm of celotex.

    Also, I wouldnt skim and attic space, if someone does investigate the works it'll probably be viewed as the start of a loft conversion.
     
  6. wuddy

    wuddy Member

    ventilation between the slates themselves.

    hallbeck is correct - i missed that about the no felt sorry
     
  7. Removed 4

    Removed 4 New Member

    It seems such a pity to burden Building Control with such a trivial matter - they're so busy at the moment.

    Just carry on regardless. Why would anyone want to pay an LABC fee for such a simple job?


    Lucia.
     
  8. hallbeck

    hallbeck New Member

    Doesn't sound simple to me - sounds like a loft conversion without installing a floor!
     
  9. Willy Duwitt

    Willy Duwitt New Member

    I was under the impression that b/regs were not required when creating a storage space in your loft, irrespective of whether you choose to insulate, plasterboard or carpet it. As long as it's not a habitable room with access via an approved stairway, I believe you can kit it out any way you want, without having to inform BC.

    I could be wrong though.
     
  10. building control

    building control New Member

    I could be wrong though.
    you could be,

    the ministry of funny walks decided a couple of years ago, that ANY work in a loft is notifiable, its ok to lay a few boards for occasional storage, but any more needs Regs.
     
  11. Removed 4

    Removed 4 New Member

    I need to put my Chrismas Decorations back in the attic. Do I have to inform by local BC?

    Some of you are are just plain crazy, others are simpletons.


    Lucia.
     
  12. johnny the m

    johnny the m New Member

    Many thanks to all - if ventilation isn't a problem would I be best to put say 75mm rigid insulation between the 83mm deep rafters then staple some multifoil sheeting to the underside of the rafters or would I have condensation issues. The headroom in the loft is so low you can't stand up even directly below the ridge line so I couldn't use the space for anything other than storage.
     
  13. ecm

    ecm New Member

    It's the law of diminishing returns with insulation so I would be tempted to just put 50mm PIR in if you are only using it for storage.

    As for informing LABC for BRegs on a retained roof for upgrading the insulation and cold bridging, come on guys - let's have a bit of perspective.
     
  14. Willy Duwitt

    Willy Duwitt New Member

    on guys - let's have a bit of perspective.

    Finally. A voice of reason
     
  15. mightyapu

    mightyapu New Member

    I think most simply stated the facts, the works require BR approval - now it's entirely up to him as to what he chooses to do about it.
     
  16. Gary wych

    Gary wych New Member

    I have a similar issue. Clay tiles, teal and mortar, mostly fallen off. 110mm rafters, 35mm gap to battens then another 20mm to tiles. 75 mm celotex then 37.5mm insulated plasterboard. All builders say no need for regs as it’s an existing attic room being improved. I’ve decided to DIY and consult a surveyor. Is 35mm airgap enouugh and do I need building regs?
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice