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General: Flat roofing

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    I'm sketching out ideas for a house design (in order to come to some reasonable figure on what a house build is going to cost, and so know how much I can afford to spend on a plot). I looks like I may have to go for a non-tiling solution on the north-facing roof because it will have a shallow pitch - in the region of 15 degrees.

    Mark Brinkley mentions Sarnafil single-ply as a possibility, but I need to get a ball-park figure for the cost. Can anyone help me? The area is likely to be a single face around 132 m^2, probably without any interruptions like Velux windows, but will have a couple of ventilation vents.

    Are there any other options open to me?

    Martin.
    • CommentAuthorpmagowan
    • CommentTimeMar 5th 2012
     
    Powder coated tin. Looks nice, cheap. Zinc or copper, looks lovely, expensive.
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      CommentAuthorfostertom
    • CommentTimeMar 5th 2012
     
    Better in every way than tin, fibre-cement corrugated.
    Onduline?
    Actually, Onduline (because it's so cheap) is also offered as a weatherproof system to go under a purely decorative cover of slates/tiles which can then be installed at too flat an angle.
  4.  
    Got Onduline on the shed, and I know some National Parks really like it, but I wouldn't saddle a house with it. Also uneasy about the longevity. 25 years no problem, but 60+??
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      CommentAuthorfostertom
    • CommentTimeMar 5th 2012
     
    Protected under tiles, prob no prob on either count?
  6.  
    Sorry, under tiles, yes, but I thought you were initially suggesting it 'naked' (the Onduline, I mean!)
  7.  
    Fibre cement tiles and then slates or tiles over that? OK - that's interesting. But two skins and the extra reinforcement in the roof to support it all might make it pretty expensive?

    Longevity is a big factor of course. Sarnafil looks like 40 years or so, which isn't great. Powder coated tin - how long would that last, and how much? Is there some source I can go to to calculate ball-park figures?

    M.
    • CommentAuthorpmagowan
    • CommentTimeMar 5th 2012
     
    Powder coated tin is not that expensive. Try google, there is a lot on t'internet re it. I looked it up to price a big garage and it seemed reasonable. I don't like the onduline as there was some of it on the garage before and it didn't seem in very good nic. Maybe it doesn't like sunlight etc but it had warped and was very easily broken.
    • CommentAuthorCWatters
    • CommentTimeMar 5th 2012
     
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      CommentAuthorfostertom
    • CommentTimeMar 5th 2012
     
    Posted By: Nick ParsonsI thought you were initially suggesting it 'naked' (the Onduline, I mean!)
    I was, as an alternative
    Posted By: palebluedotFibre cement tiles and then slates or tiles over that?
    no, Onduline (cooked sawdust and bitumen) corrugated sheeting and then slates or tiles (on battens) over that.
    • CommentAuthortony
    • CommentTimeMar 5th 2012
     
    There are tile that will get you down to 15 degrees -- whisper me for details
  12.  
    Thanks for all the help guys. Sorry fostertom, You'd just mentioned concrete blocks when you added Onduline. In my ignorance, I thought this might be the trade name for a block. Learning every day here!

    CWatters - thanks for the links, very helpful. I'm getting most of my info from Brinkley's Housebuilder's Bible, where he mentions minimum pitches for roof tiles, but it seems there are options below what he says. Thanks again.

    Hi Tony. I think I've whispered at you. I presume that's like a private message - haven't done that before.

    Martin.
    • CommentAuthorTimSmall
    • CommentTimeMar 6th 2012
     
    I'm also considering EPDM (single sheet, glued down and then ainted with acrylic masonry paint) on my 15 degree pitch extension. Might look a bit naff, not really sure yet - I'm going to try the same thing on my dormer flat roof first.

    Tim.
    • CommentAuthorRobinB
    • CommentTimeMar 6th 2012
     
    A green roof over EPDM? Better roof did the EPDM for us and I propagated sedum and planted the roof up. Very easy (my bit at least). 15 degrees would be about the limit before it would need something more complicated to stop it sliding off.
  15.  
    Robin - What sort of price per m^2 did your installer charge for the EPDM? How much more did it cost to do the green roof part?

    Also, I'm seeing claims for 50 years life (ie earliest roofs installed still OK). But these are manufacturer's claims. Do you know much about the longevity?

    Martin.
    • CommentAuthorwookey
    • CommentTimeMar 7th 2012
     
    I've got a sarnafil (PVC) flat roof (this year). Works fine so far. Was part of larger project so I can't really give a useful £/m2 price. Cheaper for large areas than small ones as most of the work is in the fiddly corners/junctions. Makes for a very lightweight roof and very well insulated as no mechanical fixings needed. Making it a green roof hides the waterproof layer from the sun so it should last approx forever, otherwise about 40 yrs.
  17.  
    Profiled metal roofing sheets, as used on large agro. buildings. Have used as a temporary cover to a blown flat roof, laid at a shallow pitch with generous laps, worked perfectly. Visually I would go for black or galvanized corrugated sheet, but then I'm strange, would have my whole house clad in it !
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      CommentAuthorfostertom
    • CommentTimeMar 7th 2012
     
    ah jus lurve ordinary corrugated iron with its speckly galv finish - trying to find a way of using it in a long-life building, but they don't claim great longevity.
  19.  
    Nice use of crinkly tin as a wall cladding at Taunton College (where the Genesis Project is also sited).
    • CommentAuthorpmagowan
    • CommentTimeMar 7th 2012
     
    I also like corrugated tin and am using quite a bit for my garage roof. I think it realistically needs to be powder coated to get longevity. We have sheds that are done in the stuff and they are relatively good 30 years later (and they were originally reused sheets not powder coated). We have had the roof repainted twice in that time. Once because there was a grant to painting sheds green (to help them blend in) and recently to help protect them and increase longevity. We are getting one roof coated in Icynene internally (to stop drips of condensation and to help with weather tightness)
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      CommentAuthorfostertom
    • CommentTimeMar 7th 2012
     
    I'm talking specifically of traditional 'corrugated iron' of 3" pitch x 3/4" depth http://www.bobhumm.com/ - which is different from modern 'profiled steel sheeting' which may be sinusoidal, more often trapezoidal in section, and of greater pitch and depth.
  22.  
    Yes, Fostertom, I too mean 'trad' 'corrugated iron'. Re longevity, I am just about to replace a big corrugated iron roof on a former hot-house. As far as the lessees know, the roof dates from just before WW2!
    • CommentAuthorpmagowan
    • CommentTimeMar 7th 2012
     
    I am also talking of traditional stuff although I may be using more modern stuff on the garage because of the lengths it comes in 9not really going to be seen much anyway. We have some nice beach huts/holiday cottages near us that are made entirely of the corrugated tin on a wooden frame. they look lovely and are very colourful.
    • CommentAuthorRobinB
    • CommentTimeMar 7th 2012
     
    Posted By: palebluedotRobin - What sort of price per m^2 did your installer charge for the EPDM? How much more did it cost to do the green roof part?


    I can't remember the EPDM price but will whisper you the supplier's details. The green roof wasn't much at all. The planting layer came from these people who were nice to deal with - not so far from us. It included a felt layer which went down against the EPDM and I filled it with lightweight topsoil from a local supplier and the sedum cost about £3 the year before.

    http://www.abg-geosynthetics.com/
  25.  
    As all this is meant to be so that I can figure roughly what I'm in for financially, I'm going to figure out a price for a couple of options. Thanks for all the suggestions.

    Martin.

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