Drainage from sinks to sewer

[dogfonos]

Would appreciate opinions on what is possibly a very simple issue but I know little about this area and it's making me uncomfortable...

We're in the early stages of planning a two room ground floor kitchen/diner and utility room extension and I'm concerned about the proposed drainage route from both kitchen (sink & dishwasher) and utility room (sink & washing machine) outlets.

The sinks and machines will not be positioned against outside walls so the proposal is to run the drains underground to join the sewer run. This would mean a drainage run beneath the flooring of the new extension of about 4 metres then another 2 metres underground outside to join the sewer (about 2 - 2.5 metres deep). Somewhere along the drainage line, the utility drain would need to join with the kitchen drain - I imagine.

What concerns me are potential blockages. Assuming the necessary safeguards are put in place (roding points, correct pipework, drops etc), is it OK to run drainage under flooring in this way?

 

[Hugh Jaleak]

Absolutely fine. Needs to be run in 110mm pipe, with reduction to appropriate waste sizes at floor level. Make sure all of the run is accessible for rodding/jetting. In practice it is not necessary to run the pipework so deep, it can be run at a shallower dept to immediately before the main sewer you're connecting to, then a 'backdrop' (or other arrangement) can be used to drop the drain to the correct depth to meet the invert of the existing sewer.

 

[loply]

In my experience the only problem with inaccessible underground drains is when they break.

And that only happens when they're made of something **** like clay, or less so cast iron.

Plastic on the other hand... meh... it'll be there in a thousand years probably.

I doubt you can block a 110mm pipe using the waste from a pair of sinks... With modern flexible cameras and fancy jiggery pokery pressure washer things I wouldn't be worried about it anyway.

 

[Nige F]

A drain can be blocked by sinks if they are on their own on a run of say 20 houses the lint from washing machines and fat from the sink combines and no WC's on the line. But I agree one house and good housekeeping, it should be fine. I would be surprised if spun cast buried drains break but I'm not sure about the suspended cast with rubber joints The Building Inspector may allow an internal "backdrop"which is easier than digging down.

 

[dogfonos]

Thanks folks - good to hear it shouldn't be a problem. Now I can move on to the next thing to worry about...