Building an Extension Part 2 – Moving drains

Roger Bisby shares the trials and tribulations of moving drains in the second episode of The Extension project.

Builders will often tell you that the hardest part of a job is the bit in the ground. In my case this was true. The ground was made up with rubble, there were two drain runs and manholes to be removed and relocated.

Thames Water won’t let you use indoor manholes because they need to get in there and pressure jet. The drains also have to be clay. I had to dig them out and build new manholes in a day so I could keep all the houses on the services.

Relocating the drains was the hardest day’s work I have done for ages and there was no time for filming so excuse the brevity of this video. I kick myself now but at the time I didn’t need any more complications.

I’m happy now we are out of the ground. I spent far too long thinking about how I was going to do that part of the job, even on holiday I was thinking about it and maybe that was a good thing because my plan went like clockwork.

For more information on relocating drains and relocating manholes in the UK, see:

The following advice is particularly relevant:

Why do I need to think about underground drainage?

You may have to change your plans to suit the depth and location of the underground drain or sewer that you intend to connect to.

If you intend to build over or close to a public sewer, you will require written agreement from your sewerage undertaker, so you should consult the company at the earliest planning stage of your building work.

Building over an existing drain or sewer can damage pipes, so that they leak or block, potentially leading to odour nuisance, health problems and environmental damage. It also makes it more difficult, time consuming and expensive to clear blockages and repair or replace faulty drains. So if there is an existing drain below, or close to, your proposed extension, it may need to be moved or protected, which is likely to increase the cost of your project.

The route of the drain should avoid obstructions (eg. ponds or outbuildings) and keep away from foundations, so may need to be longer and have additional access chambers, rather than running in a straight line. Approved Document H gives guidance on additional measures needed where drains have to run close to foundations.

In order to carry the flow and to avoid blockages, the drain or sewer that you intend to connect to generally needs to be at least 0.8m lower than the ground floor level. If it is less than this, you should seek advice from a builder, architect or drainage engineer.

About Roger Bisby

Roger Bisby is an English television presenter and journalist, known for his expertise in the British building industry.

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