Roof runoff into sewer

[morningglory]

Hi,

I've recently had an extension built and the BCO wants the guttering to run into the combined sewer with a trap. A soakaway isn't suitable as next door downhill is a big stone barn with poor footings, poor soil and is very close to my house.

It will be a huge faff to run downpipe to the existing trap or put in a new sewer trap. Can I run this through a normal 40mm domestic trap with some adapters, then into a 40mm waste pipe in a utility room? The new roof area is 12 square metres but the guttering takes rain from 25 m square.

The BCO is going to have to sign it off anyway but I'm just after anyone's opinion on here.

Thanks

 

[Nige F]

Hi,

Can I run this through a normal 40mm domestic trap with some adapters, then into a 40mm waste pipe in a utility room?
Thanks

NO

 

[Hugh Jaleak]

Second Nige's NO! Must be done in 110mm underground drain. You cannot reduce the size of the pipework, it'll rapidly block and that's if it'll take the flow in the first place. (Unlikely!) Also BCO will never sign it off. Do it once and do it right.

I would consider yourself lucky you're being allowed to connect to the sewer and aren't having to dig a hole big enough to lose a car in for a soakaway, with the resulting heap of leftover spoil to dispose of!

 

[morningglory]

I've thought of a new way to run this into an existing 110mm trap/gulley so this should be fine. Putting in a new 110mm drain would've been even more of a problem than an elephant-sized soakaway.

How come a 40mm trap can cope with the huge flow of a bath emptying but can't cope with runoff from even the smallest roof? Curious, but I can sort my problem properly anyway.