Drainage help

[SpecialK]

Hi,
Im looking to build an extension which involves moving the house roof downpipe to the side from the middle of the house (its square type guttering so should cope 10m run?)

The new extension roof would then drain over this side too.

I have an 900mm gap between the boundary and new extension wall I will need to squeeze a manhole into, keeping it as far from the new foundation as possible... can I double back the roof drain from the new extension into the new manhole? Or are there other ways such as a Y joint?

 

[oldbutnotdead]

You really don't want to double back like that- its an invitation for a blockage.
That drain- is it shared (looks as if it is)- in which case you'll need buildover agreement or (better) move it so it isn't under the new build. 800mm will be tight for getting manhole and angles in- doable if near the surface, dream on if its 2 metres down. Plus (unless you're building on clay) you ought to be looking at building a soakaway for the rainwater rather than loading the foul drainage. Which might solve your problems... or look at manhole (and guttering) on the other side of the extension

 

[SpecialK]

Thanks,
Yes its on clay and shared! Urgh. Will probably need a build over too as I'm covering more than 6m of the run and it looks like they will want ductile iron pipe, clay or plastic capable of 4000psi jet or more!

I cant really move the the drain as I want to build right up to the neighbours boundary on the other side, unless I dig up their garden for the offset which could be possible...

the drain is approx 300mm below the surface

also it isn't a foul drain, just a roofwater drain... not sure if this makes a difference

Really I need to wait and get a build over agreement to see what they want..... but I'm itching to do something!

 

[oldbutnotdead]

Maybe worth talking to your neighbours (both sides)- if they are having similar thoughts you might be able to get together & move the whole run further up the garden, though if its only 300mm below ground that might be a bit iffy in terms of protection.
Your problem might be better solved with a large water butt in the corner (which would bridge the gap from extension to boundary wall)- gutters drop into water butt, excess leaves water butt the other side into a gulley trap (which you'd have to put in with the manhole). I'd suggest IPC but they're usually a metre so won't fit.

You could try your local water company's website & see if they've got standard requirements.....

 

[Hugh Jaleak]

Rainwater unlikely to block, connect it in on a 90° junction immediately before the pipe goes under the building, and either fit a rainwater gulley or rodding access at the base of the downpipe. Or can you move the rainwater downpipe to the front and connect there?

 

[SpecialK]

This sounds like a good option, thank you. If it totally blocks its only 30cm under the ground so can easily be dug out?

Rainwater unlikely to block, connect it in on a 90° junction immediately before the pipe goes under the building, and either fit a rainwater gulley or rodding access at the base of the downpipe. Or can you move the rainwater downpipe to the front and connect there?