Changing the foul water route with an extension project

[ProBodger]

I'm on the verge of getting a house (or my other half is anyhow). It's a small semi, but with enough space for a decent sized extension. The plan is to extend to the side, the existing foul waste routes from the rear around the side and off at an angle to a newish sewage treatment plant(STP). The neighbouring semi's foul waste connects into ours at the rear (we will share our STP with next door - for now anyhow).
From what I can see, the bathroom sink/baths/showers and kitchen waste in both houses all feed into the foul waste. Neither house has seen a significant refurb in quite a while, so in our half we'll be gutting and refitting the interior (me doing the straightforward stuff as I'm no tradesman), replacing existing bathroom, adding another toilet /shower downstairs amongst other stuff.
At the rear there is a conservatory and in that floor is a manhole with big holes in it, by the smell it's for the foul waste. My questions:
- The foul waste pipes in the manhole look very shallow - no more that a foot to the base of the gully - is there a regulation about how deep they should be?
- If the foul waste needs to be deeper, would that mean replacement of next door's foul waste pipework as well?
- from reading around this forum it looks like you sometimes need to get permission to reroute sewage pipework, but does that only apply where foul waste feeds into public sewers?
- the STP apparently seems to cope with all the grey waste water it's taking (it's not a big volume tbf, and it's just had a service and the report looks fine) - anyone have long term experience with these?

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[Hugh Jaleak]

There is no minimum depth for a sewer, but they need to be protected from damage, so anything too close to the surface would normally be covered with concrete to provide the required protection. You can put yours in deeper should you want to, bear in mind it'll need a constant fall to the Treatment Plant, no need to alter the neighbours, just ensure the drop into your new lower system is done correctly to avoid issues.

I would consult Building Control at your local Council before altering anything, they may not be bothered, but if the work needs Building Control approval, its easier at the time than getting it retrospectively.

Treatment Plant, same as any system, be it a basic septic tank, right up to a packaged treatment plant, once it has been initially filled from empty, every drop going in needs to displace the equivalent volume out, so it depends entirely on the outfall arrangement as to what it'll handle. Round here we have clay soil, and I've seen tanks after being emptied, that are rapidly refilling from the outlet, as the Soakaway/Leachfield is completely waterlogged and the outlet is acting as a Land drain. The systems simply do not work, as they just fill up and stay full, meaning constant Tanker visits to remove effluent.

Others, like the Klargester Biodisc, produce, (if maintained correctly and in good working order), a clarified effluent that can be discharged straight into a watercourse. As with any system, it needs to be sized to the required usage.

 

[ProBodger]

Cheers for that. The STP is only a couple of years old (I've seen the installation paperwork, done by a reputable local specialist), apparently fully compliant with environmental standards and discharges nice clean water via a shared outflow pipe to somewhere about half a mile away. I'm slightly wary of rousing the local council, but will contact Building Control (assuming the sale doesn't fall through).