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Housing - New Build: Very Thin Warm Roof Challenge

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  1.  
    Posted By: SteamyTeaUsed to make insulated curved GRP roofs for steam rooms. Largest I made was a 5.5m span. Never had to worry about snow loading, just a fitter/maintenance person crawling over them. Not something I would want to do on site though.


    I'm thinking onsite is the way - you guys think buying it in pre-built is easier?

    I was thinking (like JSH said) building a former on stilts, then building up the ply in thin layer, and the insulation in thin layers, all in situ.

    The fibre glass is the bit I know little about. You think its feasible to spend a weekend or two up there laying it myself? I guess the finish wouldn't be too critical as it'd be covered over with metal.

    Perhaps that is the bit to get a fibre-glass roofer in for - although don't know if there are many of them in Aberdeenshire!
    •  
      CommentAuthorjoe90
    • CommentTimeNov 7th 2011
     
    thomasjamesrhodes,

    Grp is not difficult, my local supplier does 1 hour courses (for free) on the basics and is always willing to answer questions and give advise. I wonder if the metal cladding is necessary as a top gel coat for the GRP is very close to the colour of lead and difficult to tell the difference from the real stuff. Also lots of pre-made upstands, angles etc available off the shelf.

    I do GRP flat roofs/gulleys etc and its easier (IMO) than lead (and no-one going to nick it :smile:)
  3.  
    In case anyone is interested (who knows there may be others) here is the key passage in the Scottish Building Regulations Technical Handbook that outlaws cold deck roofing:

    However cold, level deck
    roofs, should be avoided because interstitial condensation is likely and its
    effect on the structure and insulation can be severe and many instances of
    failure in such systems have been recorded. It is considered that more
    reliable forms of construction are available. Both the warm deck and warm
    deck inverted roof constructions, where the insulation is placed above the
    roof deck, are considered preferable. However fully supported metal roof
    finishes including aluminium, copper, lead stainless steel and zinc are
    regularly used in conversion work, and they should have a ventilated
    airspace on the cold side of the insulation in addition to a high performance
    vapour control layer near the inner surface. Further information may be
    obtained from the relevant metal associations.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 7th 2011
     
    Making sure everything is bone dry is the real problem with GRP.
  5.  
    Posted By: joe90thomasjamesrhodes,

    Grp is not difficult, my local supplier does 1 hour courses (for free) on the basics and is always willing to answer questions and give advise. I wonder if the metal cladding is necessary as a top gel coat for the GRP is very close to the colour of lead and difficult to tell the difference from the real stuff. Also lots of pre-made upstands, angles etc available off the shelf.

    I do GRP flat roofs/gulleys etc and its easier (IMO) than lead (and no-one going to nick ithttp:///newforum/extensions/Vanillacons/smilies/standard/smile.gif" alt=":smile:" title=":smile:" >)


    Hi Joe90

    Thanks for that, its good to hear. I'm almost convinced that it would be noticed if we went for GRP, the listed building people will be doing inspections and I can't see them letting that pass! Its a shame, cos the roof is hardly going to be seen. I wonder if we'd get away with metal soffits and box gutters, and a GRP roof...

    To SteamyTea - things don't ever get bone dry in Scotland, so that's probably worth considering...

    Cheers
    Thomas
  6.  
    In my ongoing quest to find out about putting a metal roof onto a warm deck, I've come across this interesting article:

    http://www.buildingconservation.com/articles/leadsheetroofs/lead-sheet-roofs.htm

    "Whether a warm roof or a cold roof is specified, there should be adequate provision for ventilation as shown in Figure 3 (left). It is essential that there are no stagnant air pockets and that there is proper circulation of air to all parts of the decking which support the lead covering"

    That answers it pretty well.. I'd need to finish my structural panel, then put spacer batons on to create an air-gap then another 18mm of ply, then underlay, then metal. stacks up, doesn't it?

    Does anyone know what minimum size an air-gap has to be to be considered acceptable? 25mm?
    • CommentAuthorSteveZ
    • CommentTimeNov 7th 2011
     
    Hi Thomas

    Without wishing to divert you from your plan to build a beautiful curved roof, have you seen this earlier thread?

    http://www.greenbuildingforum.co.uk/newforum/?CategoryID=3

    I can't understand why a warm deck with a vapour barrier on the bottom and another sealed waterproof layer on top needs ventilating - just as well I'm not a roof designer or a buildings inspector :wink:
    • CommentAuthorchuckey
    • CommentTimeNov 7th 2011
     
    Have you considered Corus sandwich roofing decks. Its the stuff they use on the roofs of the "big shed" DIY places.
    Frank
  9.  
    The Speeddeck roof seems quite thin and has some other advantages! http://di.speeddeck.com/
  10.  
    Posted By: SteveZHi Thomas

    ...have you seen this earlier thread?

    http://www.greenbuildingforum.co.uk/newforum/?CategoryID=3" rel="nofollow" >http://www.greenbuildingforum.co.uk/newforum/?CategoryID=3



    Hi Steve

    I'm afraid I can't find the specific link that you refer to, your link seems to take me to the default folder. I have seen the thread about a guy wanting a thin roof, where he explores the use of solid glu-lam decking - is this the one you refer to. I was quite intrigued by this technology, but I suspect its too expensive for my house!

    Is this the thread you mean?

    Cheers
    Thomas
    • CommentAuthorSteveZ
    • CommentTimeNov 8th 2011
     
    It's in Housing - New Build page 9 or search for 'Warm roof construction, EPDM directly onto insulation?' It is not clear how the project turned out, but it may be that he put the EDPM membrane directly on to th einsulation and weighted it with ballast. May not suit your planners anyway.
  12.  
    Hi all

    I thought an update might be in order. Finally got the rubber stamp on the planning permission for my extension, including challenging thin roofed link. I've spoken to a few people about it, had a few ballpark responses from a couple of SIPS companies, and developed the idea some more.

    I'm still awaiting a price from the most pro-active and local SIPS guy, who has been very encouraging and positive about the idea, though he is fairly sure we'll need to integrate steelwork spanning either side of the link (from old building to new). This can be done within the overhanging eaves, removing the thermal bridging issue, so may be a good solution. I am, however, still confident it could be done without the use of steel, potentially still laid in situ.

    My plan is to do some detailed drawings and seek further advice, possibly from a naval architect, for whom this kind of thing must surely be closer to their comfort zone.

    I am currently thinking (from top) standing seam lead roof on lead-roofing paper, 18mm ply; 25mm airgap (batons); VPU; 25mm ply bonded to 100mm rigid foam bonded to 25mm ply; vapour barrier; 13mm plaster board. All elements would be gently cambered, with lead clad box gutter soffits.

    I'll keep you updated.

    Thomas
    • CommentAuthorqeipl
    • CommentTimeDec 6th 2011
     
    Posted By: thomasjamesrhodes

    I am currently thinking (from top) standing seam lead roof on lead-roofing paper, 18mm ply; 25mm airgap (batons); VPU; 25mm ply bonded to 100mm rigid foam bonded to 25mm ply; vapour barrier; 13mm plaster board. All elements would be gently cambered,..


    You might struggle to bend (and keep bent) 25mm ply. Two layers of 12mm ply would be hard enough. Three layers of 9mm sounds easier.
  14.  
    hey all, another update 3 years later, the roof is built.

    http://tollstension.wordpress.com/2014/09/25/zinc-roof-finished/

    details are on my blog but in the end we went for :
    lowered floor level (managed to get a concession there, thank goodness) by about a foot
    arced steel beams with joists sitting within them.
    2 layers of bonded 9mm marine ply, arced across the top
    3 layers of 50mm ecotherm insulation, bonded and arced
    2 more layers of ply
    breather membrane and zinc.

    thanks again for everyones help.
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2015
     
    Posted By: thomasjamesrhodeshey all, another update 3 years later, the roof is built.

    details are on my blog but in the end we went for :

    Congratulations! Have you got a direct link to the blog entries with the details?

    lowered floor level (managed to get a concession there, thank goodness) by about a foot
    arced steel beams with joists sitting within them.
    2 layers of bonded 9mm marine ply, arced across the top
    3 layers of 50mm ecotherm insulation, bonded and arced
    2 more layers of ply
    breather membrane and zinc.

    What radius is your roof? Ours is 6.5 m and we used two layers of 9 mm French structural ply. The interesting thing about ours is the lack of ventilation, thus avoiding another two layers of ply and a layer of battens. It relies on an 'intelligent' membrane both top and bottom and hygroscopic insulation (recycled newspaper) in between. Guaranteed by Pro Clima, but I have two humidity sensors just under the top of the ply to try to catch any problems developing before they become terminal. I don't see mention of ventilation in your buildup either?

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