New drain

[brucep]

I’ve recently had a new drain put in partly to replace an old one, but also to re-route it because of an extension I’ve had built. The new drain runs from a gully, half way along one side of the house, across the back and into a manhole on the edge of the lawn. This has meant 3 new inspection chambers have had to be installed as well. I thought for a drain there had to be a continuous fall, and in order to do this, it would have been easiest to have started at the gully and worked backwards towards the manhole. My builder didn't do this though, rather he installed the 2 chambers closest to the manhole first, before finishing off the rest. Doing things this way, I’m curious as to how he would have known how deep to set the chambers to get the fall right, because I’m not sure it is. When I run water into the gully, about 2” always remains in one of the chambers and it never clears. Is this ok?

Appreciate any comments
Thanks
Bruce

 

[theoldun]

You can lay drains up hill or down dale, but we prefer to work from lowest invert to highest invert on long runs. Just matter of preference
Levels are simple, say you have10m run of drain and there is 200mm difference in invert levels, divide 0.200mm into 10m = 50. Therefore your fall is 1 in 50. Now divide 50 into 1 = 0.020mm. Therefore your fall is 20mm for every metre run. Check it back 10m run by 20mm fall = 200mm.
Now work this one out for yourself. 25m run and 350mm fall. Answer should be 0.014mm fall every metre.
Yer man has made a clanger, if you have got 50mm water laying in chamber, it will also be laying in pipes either side of chamber. If chamber is only serving external gully, then no big sweat, except that if you pour a lot of fat down sink, over a period of time you will get a build up where water is laying.
If pipe was running solids and depending on fall and flow then you could have a lot of problems.
50mm back fall is not really acceptable, but if no solids on run is liveable, providing run is 100% watertight.
This is a major problem when re routing a drain for extension, gaining sufficient fall.
Guidance only. Your decision.
old un.

 

[Richard C]

I assume Building Control didn’t inspect it then as there is no way they would have passed it; are they inspecting your extension You should not have water lying in the drain runs or inspection chambers or you will get problems; the only uncertainty is how long you will have to wait before they begin! This will be largely dependant if it’s surface or foul water, not long in the case of the later. Get your builder to rectify it or keep the phone number of your local Dyno Rod handy & a shoe box full of cash to pay for power flushes.

 

[Nige F]

Shoe box - Tea chest more like

 

[theoldun]

All very well, providing he can get builder to come back and rectify.
old un.

 

[brucep]

Thanks for the replies. The inspection chamber with the standing water is also fed from a new soil stack, which connects to a toilet, bath & shower. Building Control haven’t inspected it yet, but the drain has already been covered over & the trenches filled in. I'm assuming this shouldn't have been done yet?

Bruce

 

[Richard C]

LABC require to inspect new drain runs & inspection chambers BEFORE the trenching is backfilled so you could have a wee problem there; they can also require to witness test on the new drain, sometimes they do & sometimes they don’t.

Have you had any inspections on the extension build depth of footings would be the first with several more after that as the build progresses. Your Builder (if that’s what he actually is) will know this but it’s ultimately your responsibility to comply with B Regs so if you have a cowboy on your hands, you could be heading for all sorts of problems.

 

[Hugh Jaleak]

You need to get this sorted NOW!!!! If your builder cant even lay a sewer to the correct fall what else is going to get bodged? You may just about get away with a backfall on a rainwater drain or one serving just a gulley, but from a W.C. then problems will soon manifest. Solid matter will 'stick' in the low point, eventually building to block the pipe... B.C.O. will not pass that drain unless he comes with a white stick.

The lot needs to be dug out again, the pipes set to correct fall and approved by B.C.O. before going any further at your builders expense, otherwise you will be heading for a lifetime of problems. Seems a strange method of working he's adopted, but even so, if the levels are calculated correctly then this sort of problem should not occur.

 

[Nige F]

LABC require to inspect new drain runs & inspection chambers BEFORE the trenching is backfilled so you could have a wee problem there; .

or a poo problem

 

[Richard C]

Took a while - boom, boom