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How to do 5m "horizontal" valley

Discussion in 'Roofing and Guttering' started by bazmdiy, 27 Aug 2012.

  1. bazmdiy

    bazmdiy

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    Hi all – Please can someone help with the detail of a “horizontal” roof valley?

    I am building a single storey extension made up of 2 pitched roofs. The valley in between is 5m long and horizontal (but can be made to have a slope of say 30-40mm in 5000. The base of the valley is a 5m 250mm oak beam. The valley discharges water onto a pitched eaves.

    My original instinct was to have a 5m run of lead but reading about the minimum recommended lengths of lead I’m now having second thoughts.

    Does anybody have experience of creating such a valley and is there a danger of condensation under lead?

    I attach drawing.

    Many thanks

     
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  3. doitall

    doitall

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    Lead is the best if it's done properly, and also oiled when finished.

    You should have a roofing paper under the lead.

    Best get a roofer that does lead work.
     
  4. ^woody^

    ^woody^

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    You can't have a flat horizontal lead gutter 5m long. It will have to be stepped

    EPDM in one peice may be better
     
  5. doitall

    doitall

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    You could if both ends are floating.
     
  6. Roofer

    Roofer

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  7. doitall

    doitall

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  8. Nige F

    Nige F

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    A big consideration with the planned gutter - is access to clean out leaves/debris :idea:
     
  9. bazmdiy

    bazmdiy

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    Hi all and thanks for enlightening replies.

    Doitall got me thinking. I think there may may an exaggerated fear about the expansion of lead so I looked up the extent of the problem...

    It turns out that 1m of lead will expand/contract 0.028mm for every 1°C rise/fall in temp.

    If I lay my lead at 15°C and the temperature rises/falls to say 45°C/-15°C then 1m of lead will expand/contract by 0.028 x 30 = 0.84mm. 5m will expand/contract by 4.2mm. If the lead is fixed in the middle (or even unfixed) it allows the ends to expand/contract by 2mm. I think this is manageable.

    I would go with lead if anybody can advise about condensation?

    Cleaning the valley is not a problem - access via flat roof.

    Roofer - I found the t-pren joint would do the job but it would require someone to weld and it would treble the price of the job. I think it would ideal for a very long gutter.
     
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  11. Nige F

    Nige F

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    have a look @ www.leadsheet.co.uk/lsa-pocket-guide Substrate underlays and ventilation :idea: you might get away with one length if it`s free to move and not nipped anywhere by tilebattens etc. I did a job some 25 years ago with a sheet aprox 7 foot by 3 foot over a lean to kitchen roof extension - One concealed fixing in the middle of the sheet on a 20 degree pitch . NOT to spec as it should have been copper nailed @ the top - but I went there again recently with the builder ( a glass panel in the roof had cracked ) and the lead hadn`t moved at all ;) . I said @ the time , if there was any trouble I would have done more fxings Free of Charge - seeing as I reckon I`ve got 25 years left where I could still do it - I`ll call it a Lifetime guarantee :LOL: . I went to school with the builder .We both left in 1970 . Why wasn`t it fixed @ the top with copper nails , because the lead laid on a sheet of celotex insulation - so you`d have been hard pressed to get nails long enough . Good enough for a country job by a P*key Plumber
     
  12. doitall

    doitall

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  13. Roofer

    Roofer

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    When lead is laid in oversized lengths or bays, failure (cracking) occurs because of metal fatique.

    If the lead is in a sunny, exposed situation then this failure is much more likely to happen than in a shady, sheltered situation.

    But there is no way that you can lay lead in a continuous 5 metre length without early failure.

    This table shows maximum recommended bay sizes


    http://www.leadsheetassociation.org.uk/maximum-recommended-sizes-of-sections-bays-and-panels
     
  14. Nige F

    Nige F

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    Well I was thinking the OP would use code 8 lead ;)
     
  15. bazmdiy

    bazmdiy

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    Lots of ideas - thanks very much. I've now got a lot more confidence in this job :p

    Sensibly it would appear that 3 t-pren expansion joints would be the way to go. But I think it will look ugly and be a big expense. I can't have drips unless I expand up the rafters but I'll see how bad that looks. Will also see if I can get a middle joint so half the rainwater goes to the flat roof. Thanks for the Geotile tip and the lead assoc guides.

    Nige F - I'm suprised you thought I was thinking of code 8 lead - I thought maybe code 15 (6.35mm thick) :mrgreen:

    Another reason for having second thoughts about a single lead piece is the weight issue - code 5 at 6m x 600 = 91.5kg :!:

    I'll post my solution when I get there...

    Many thanks
     
  16. hardmetalking

    hardmetalking

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    Just finished 4 of the same in Middlesex. We used 0.4mm stainless steel. The whole thing weighs less than 20kg and is guaranteed for over 100 years. To avoid the condensation issue I would bituthene the valley first, always good practise.

    £500 cash supply and fix including lifetime guarantee.
     
  17. ^woody^

    ^woody^

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    You would be foolish to think that is how lead will expand.

    Your gutter will be subject to differences in exposure and temperature along it's length, and the expansion/contraction will never be linear over the whole section length.

    It will develop fatigue cracks every 1-2m if you use a single length
     
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