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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorphil303
    • CommentTimeNov 6th 2015
     
    My build is coming along, I'm getting the roof structure on but having second thoughts on finished covering.

    Now the structures up I realise how little I actually see of the roof, it's 5degree mono pitch, bungalow, with parapet wall around.

    The original plan was Tata steel colour coat urban, 120sqm, materials about£5,500, install myself.

    I can just see the final couple of meters at the top but that's it! And it's got me thinking this is a waste of money.

    I'm pretty well insulated with 165mm PIR under a deck of 18mm OSB3, finished off with a breather membrane, so noise shouldn't be an issue, I actually really like the sound of rain on metal anyway.

    I'm looking at using corrugated steel as an alternative but not sure if it works with such a low pitch? I can imagine wind driving it up, that would then rely on the membrane to drain it all and its a bit of a risk with all the fixing holes you make attaching the sheets

    Does anyone have a better idea On how to fix without puncturing the membrane so much?
    or another more cost effective solution?
    Open to ideas!

    Cheers
    Phil
    • CommentAuthorphil303
    • CommentTimeNov 6th 2015
     
    Should have said roof is 10m wide by 12m long roughly.
    • CommentAuthortony
    • CommentTimeNov 7th 2015
     
    Corrugated will leak at that pitch, lead, asphalt, elastomeric felt, in that order would be my choice.
    • CommentAuthorBeau
    • CommentTimeNov 7th 2015 edited
     
    Not sure what profiles are available but think http://www.cladco.co.uk/ can make any length you want. Transporting that length might be costly though
    •  
      CommentAuthorfostertom
    • CommentTimeNov 7th 2015
     
    No need to do it in single length - sealed laps are commonplace. Are you talking about 3" x 0.75" 'corrugated iron'? Wonderful stuff - I use it wherever poss, one domestic job completed @15o pitch, another about to start @12o pitch, another just in for planning - Dartmoor National Park Authority!

    But Cladco says 10o minimum pitch, but I'm not sure why - what's the risk, as long as there's some minimal pitch? Why should the laps leak, esp if sealed (or in unbroken length)? Is it the gasketed fixing screws, which go through the raised crowns, not the valleys? If they're going to leak, what difference does pitch make?
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 7th 2015
     
    Won't wind blow the rain up though the gap at a low pitch.
    • CommentAuthortony
    • CommentTimeNov 7th 2015
     
    Yes, and it will track over thr humps
    • CommentAuthorBeau
    • CommentTimeNov 7th 2015
     
    Don't think water getting through is the issue as you should use mastic tape on the joints anyway. Seem to remember the chap from Cladco said water sits in the joint below the seal and this hastens corrosion of the sheets.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 7th 2015
     
    When I think of water, or more importantly, how to stop it getting in, I always think of boats.
    They put a pump in :wink:
  1.  
    I have a fairly exposed 12' x 18' conservatory with a tin roof at - I think - 7 degrees, and that has been fine for a
    couple of years. Very cost effective.

    I used single pieces of the full front-to-back about 800 wide, using plasticoated corrugated steel.

    There's a thread about it somewhere - take a look through my archive.

    Ferdinand
  2.  
    • CommentAuthorJeff B
    • CommentTimeNov 7th 2015
     
    We had a low pitched box profile coated steel roof on our garage and utility room in our previous property. It was ok until it snowed. The melting snow caused water to track under the lead flashing at the house roof end - not nice - a right mess! We ended up replacing the lot with fibreglass, lapped up well under the first row of roof tiles. No problem thereafter.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 7th 2015
     
    That's a good warning Jeff - thanks.
    • CommentAuthortony
    • CommentTimeNov 8th 2015
     
    Was that a problem with the steel? Or the installation/specification?
    • CommentAuthorTriassic
    • CommentTimeNov 8th 2015
     
    Isn't it called an ice dam in Canada, snow holds back a pool of melt water that tracks into house?
  3.  
    How much are you being quoted per sq. metre for the Tata colourcoat?

    Seems like it is very expensive.

    I'm in Sweden and used a similar product from Plannja on my roof, the profile I used is called Plannja Pannplåt (you can google to see what it looks like) although Plannja Modern is probably closer in appearance to the Tata Urban.

    The current price here for Plannja Pannplåt is 179SEK/m² about £13.75/m² and Modern is 235SEK/m² about £18/m² both including VAT @ 25%

    When I did my 220m² roof a few years back I paid approx. £4,950 inc. VAT for all the materials including all the rainwater goods.

    I'd suggest you price around to see if you can get a better price than you are currently being quoted for the Tata.

    Plannja do have a distributor in the UK but I don't know how the prices you get compare. AFAIK the profile I used is made in their Polish factory.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 8th 2015 edited
     
    Ice dam - that's right - but it should equally happen with any top abutment flashing over any pitched roofing - slate, tile ... must be more to do with ultra-low pitch.

    Reason it doesn't then happen with typical flat roof abutting a wall, is that the flat roofing membrane is turned up the wall, unlike with a flashing just lapping down over pitched roofing.

    So, with ultra-low pitch, sheet end laps have to be sealed, and so also do top abutment upstand pieces having matching corrugated skirt, have to be sealed to the top sheet. Those are available - but don't work when the corrugations are other than 90o (on plan) to the wall they're abutting. Like on my current low-pitched corrugated roof project. Damn. (ice damn in fact).
    • CommentAuthorJeff B
    • CommentTimeNov 8th 2015
     
    Posted By: tonyWas that a problem with the steel? Or the installation/specification?


    It wasn't a problem with the steel itself but rather the ultra-low pitch (I can't remember what it was but is was very small, maybe 3 degrees?). We used the foam profiles supplied with the sheeting under the lead flashing and siliconed it in place. We never had a problem when it rained, only when there was snow. Back then I don't know if expanding foam was available but if I was doing a similar job today I would try squirting some of that under the lead too. Is expanding foam waterproof after curing?
    • CommentAuthortony
    • CommentTimeNov 8th 2015
     
    Yes, but would you want to rely on it to keep water out?

    There must be a proper abutment detail for profiled sheets.
    • CommentAuthorringi
    • CommentTimeNov 8th 2015
     
    Glass fiber? (To connect the sheets to lead flashing or the wall.)
  4.  
    Can't you just increase the overlap to compensate for the low pitch?
    • CommentAuthortony
    • CommentTimeNov 9th 2015
     
    Better no overlaps, we have a problem at the top of the roof
    • CommentAuthorJeff B
    • CommentTimeNov 9th 2015
     
    Posted By: tonyYes, but would you want to rely on it to keep water out?

    There must be a proper abutment detail for profiled sheets.


    No, I know what you are saying Tony but in my case there was nothing else I could do at the time.

    Had a quick browse on the web today and came across this product:

    http://www.uksealants.co.uk/illbruck-fm617-high-yield-expanding-foam-%28hand-held%29-540ml--p220.html

    Looks like it would have done the job. No connection with the company BTW!
    • CommentAuthorgyrogear
    • CommentTimeNov 12th 2015 edited
     
    AFAIAA, ice-damming can occur irrespective of pitch: it is generally due to "leaky" or failed roof insulation, melting the lower layer of snow, which as water runs down towards the eaves, except that the further it runs, the more it cools down, until it freezes. So never reaches the eaves to run off, but creates the "ice dam".

    The other problem being, the interstitial air gap between the roof and the snow is now COLD... encouraging further heat-loss through the roof (whereas the snow was previously keeping the latter warm...).

    Next day's warm leak idem, melts a bit more snow, the melt water runs down to the dam;
    next day's meltwater now backs up the roof until it finds a hole or a gap to sneak into...

    gg
    •  
      CommentAuthordjh
    • CommentTimeNov 13th 2015
     
    Posted By: gyrogearthe further it runs, the more it cools down

    I expect the effect could also occur on roofs like mine, where most of it has insulation directly underneath but the overhanging eaves just have cold winter air underneath. I'll be interested to see what happens if we get any cold periods this winter.
    • CommentAuthorEd Davies
    • CommentTimeNov 13th 2015
     
    Apart from wind uplift, I suspect that ice damming is a major reason that Highland houses traditionally don't have eves. Also, eves are to help keep the rain off the walls but if the rain isn't near vertical they don't help anyway.
    •  
      CommentAuthordjh
    • CommentTimeNov 13th 2015
     
    Posted By: Ed DaviesI suspect that ice damming is a major reason that Highland houses traditionally don't have eves.

    I expect it's just that the Scots don't want to pay for the extra rows of tiles :devil:
    • CommentAuthorEd Davies
    • CommentTimeNov 13th 2015
     
    Yeah, that as well.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 13th 2015
     
    Sods of turf originally, slates later - that's why! In the south, thatch originally made the overhang but no timbers there to do same when replaced by slate/tile
    •  
      CommentAuthordjh
    • CommentTimeNov 13th 2015
     
    Posted By: fostertomSods of turf originally, slates later - that's why! In the south, thatch originally made the overhang but no timbers there to do same when replaced by slate/tile

    Interesting. What did they use to support the sods?
   
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