drain alteration

13 Apr 2006
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United Kingdom
A friend has a house built in 1906 which now has a leaky drain. The building has a two pipe system and the problem is with the rainwater downpipe and kitchen waste. There is a trapped open gully which takes the kitchen sink and washing machine on separate discharge pipes, the gully also has a 4" side connection with the cast iron rwp connected to it. I understand why the trap is there however if we were to do away with the open gully could we lose the trap as well and rely on the sink/washing machine traps. Would there be any problem with everything connected together into a new connection straight into the clay pipe.

Thanks Martin
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Not really a plan, if it is a two pipe system the rainwater should be separate from the kitchen waste.
As above, rainwater needs to be seperate. Needs to be drained via a trapped gulley, direct connection to the drain would allow the RWP to act as a vent for the sewer, which may cause problems with foul air entering the roofspace or exiting at unsuitable points on the property.

If current broken drain is replaced with plastic, then existing arrangement should be fairly straightforward to emulate.

I am somewhat confused, why does rainwater have to be separate form waste. Virtually every pre war house here has a vented soil stack and a waste stack to which everything else is connected rain baths basins and sinks. I can see the need for a trap but not for separation of different types of waste. Is this possibly a difference between English and Scottish building regulations at that time?

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Buildings of that era had a Combined system of drainage, whereas all discharges went into the one sewer, eventually finding it's way to the Sewage works. Problem then arises during heavy rainfall, when the sewers become overloaded, and the works cannot cope with the influx of water, hence why foul and surface drainage is kept seperate as far as practical nowadays.

There is no problem with you discharging the rainwater to the sewer on the property as it always has done, but the rainwater connection must be made via a trapped gulley. Connecting sink wastes etc directly to the drain is not a problem as the sink etc will have their own traps fitted. If the rainwater connection is made directly to a combined drain then there is no provision for the rainwater pipe to be trapped, and sealed off from the sewer, it will also contravene Building Regs!

Direct connection would allow the rainwater pipe to act as a vent for the sewer, which may allow foul air from the sewer to enter the roofspace or other areas of the property where it is not desired! Vent stacks should always terminate above eaves level, or if on a gable wall, well away from any window or other openings into the building where foul air will not cause an annoyance to occupants.

Thanks v much for the explanation, most helpful. I can now see how my friend and I need to take this forward and replace the leaky bits.


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