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Flat Roof drain pipe

Postby homesolutions » Sat May 03, 2008 10:39 pm

My friends new house has a large flat roof and i have noticed that the drain pipe for the roof above just has a pipe running to the flat roof and is then left to dispell it water on the roof.
Is this normal or should it run to another gutter.
The only gutter i could run it to would be where the sink waste comes out and would this be ok?
Thanks for your help.
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Postby welsh brickie » Sun May 04, 2008 9:54 am

yes its ok for surface water to run onto flat roof ie:rain water
But foul water such as bath water,toilet waste etc must be disposed of
through soil pipes and gulley systems.
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Postby LCL » Sat May 17, 2008 5:41 pm


I actually disagree. My opinion is that if you direct water discharge from a higher level roof onto a flat roof, you will promote premature failure of the flat roof covering as it is working twice as hard.

In periods of summer rain, the flat roof can also dry out quite quickly, but the rain water may trickle fromt eh raintater pipe for some time, this will cause temperature differences in the felt (assumed) (ie cold where wet and warmer where dry) and will also act to cause failure.

There should not be an issue of discharging storm water into foul, so you solution sounds Ok, and certainly better than the current situation.

Hope this helps

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Postby smashngrab » Thu May 22, 2008 8:37 pm

Putting rain water into a foul pipe isn't allowed here,just imagine if everyone starts doing it.Nice storm,drains cant cope,crap all over the streets!Thats why we have sepperate rainwater systems.
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