Waste pipe v soil pipe: the differences

Waste pipes and soil pipes both carry used water to the sewers from your home. However, there are important differences in the functions and requirements of both types of pipe.

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What are soil pipes?

Soil, or soiled water, is water which has been used in your bidet, toilet, or urinal. It is carried away by soil pipes to connect with the sewer network. Although they also carry water away from the home, soil pipes have a much greater diameter than waste pipes. Soil pipes range in diameter from 110mm to 160mm.

Odours and gases can build up in soiled water. For this reason, the building regulations provide that soil pipes must be vented: https://www.planningportal.co.uk/info/200130/common_projects/15/drains_and_sewers/2 . The vent is usually very close to the top of the building to allow gas to escape safely and to reduce any odours. This is not just for comfort and to reduce odours, but also because the gas from soil pipes can be harmful making it advisable to have the ventilation near to the top of the building.

Soil vents and outlets are important in regulating pressure in the soil waste system. They function not only to provide ventilation but also to ensure that waste is not pushed back by positive pressure to your toilet or sink.

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Protecting soil pipes

As we have seen, soil pipes are often external to the property and are always vented externally. Broken soil pipes are an increasing problem. Pipe protectors, such as https://www.meterbox.co.uk/pipe-protectors, help protect soil pipes and other external pipework against weathering or vandalism. Pipe protectors, available in a range of colours to match your exterior and other drainage goods, provide a long lasting solution to these problems.

What are waste pipes?

Waste pipes transport used water from household fittings and appliances for example the bath and shower, washing machine, dishwasher and sinks. The water is taken by the waste pipe from your home into the connection with the sewer. Waste pipes only carry used water, not soiled water, so they do not need to be vented in the same way as soil pipes. Waste pipes range from 32mm to 50mm diameter and can be made from uPVC. Push fit and solvent-weld options are available. Push-fit waste pipes with their ring seal joints can be installed easily making them popular with those carrying out DIY.


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