Guttering downpipes


Can anyone tell me if there is an appropriate BS, or failing that just a standard recommendation, for how many downpipes a given run of guttering needs? I used to have a 40' run of roof with a downpipe at each end of it, but following an extension I now have a single downpipe at one end of a 60' run of roof, and the builder assures me that is sufficient to cope with the amount of rainwater the complete roof generates. For clarification, the roof has an approx. 30 degree angle and is roughly 20' of roof, from gutter edge to ridge tile (or 1200 square feet of roof for a single standard downpipe which feeds into a soakaway in the garden rather than a main drain). thanks in advance
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On Wed, 08 Aug 2007 13:54:34 GMT, a particular chimpanzee, nullified

Even better than that; it's covered by Part H of the Building Regulations. See Approved Document H on the Planning Portal website.
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wrote:

Many thanks for that. I've read it, several times, and the relevant bit appears to be on page 41. I'm damned if I can work it out though - the chart shows with an angle of 30 degree you should multiply the roof area by 1.29, which gives me a rough effective roof area of 140 sq. m. The chart only goes up to 103 sq. m.!
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On Wed, 08 Aug 2007 20:09:15 GMT, a particular chimpanzee, nullified

The factor is only if you've measured the plan area. Assuming your 20' from ridge to eaves is measured on the slope, you don't need to multiply it by any factors.
One can use the chart to work out how big your gutters need to be and how far apart your downpipes need to be. So in your case, with a 6.10m length of roof, a 100mm gutter and a 63mm downpipe could drain an effective run of (37m^2 / 6.10m =) 6.07m. In other words, you would need a downpipe every ~6m.
There are the other provisos that the distance from a stop end to the downpipe shouldn't be more than 50x the gutter depth, ie. 50 x 50mm 2.5m for a 100mm gutter, and that there shouldn't be more than 100x the gutter depth between downpipes, ie. 100 x 50mm = 5.0m.
The guidance is for basic gutters. Proprietary makes will have their own flow rates.
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Have a look at :- Page 5 http://content.wavin.com/__C1256AF4003281D0.nsf/0/3C78E3CC67B6C3AF8025721E003FB2DB /$FILE/RainwaterGuide.pdf
Or
http://tinyurl.com/3849kq
Baz
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