Drainpipe drain diameter and minimum slope

[kingkevbo]

Hi,

Not sure if this is a pluming or a building question really, but guessing closer to plumbing.

I will be digging up the patio area as part of the reconstruction of my house, and I will have the opportunity to lay some rainwater drains to remove the current situation of the rainwater running from the down pipe, over the patio to the nearest drain.

I can run a pipe underground to that drain when I have the ground dug up, so I wanted to ask what the diameter and slope angle should be?

Thanks.

 

[Ian H]

110mm pipe and 1/40 fall (2.5cm per meter)

 

[Hugh Jaleak]

Also, if connecting to a combined drain you'll need to fit a trapped gulley at the bottom of the downpipe. Permission will need to be sought from Building Control at the Local Council though if making connection to a drain where there want one previously.