Soil pipes running through a home take the waste from appliances and direct it towards the sewer system. When waste water flows inside a soil pipe, as when a WC is flushed, negative pressure builds up inside the pipe causing a siphoning effect. Water always flows form an area of high pressure to an area of low pressure. The force of the water being exerted from a pipe is proportionate to the height of water pushing down. When a siphon is introduced, there is nowhere for air to get into the siphon as it’s full of water and a vacuum is created inside the pipe due to the difference in pressure between the internal and external environment. If this pressure is left unchecked, water would be siphoned out of the traps in the bath or sink which would allow drain odours to enter the bathroom or kitchen. What we see in the picture is the traditional way of preventing this from happening, which is to have a vent pipe connected to the drain that is open to the atmosphere. As the siphoning pressure builds up inside the soil pipe, air is drawn in through the open vent pipe to balance the negative pressure.
Approved document H – Drainage and waste disposal requires that the foot of the discharge sack should have as large a radius as possible. Ventilating pipes should be finished at least 900mm above any opening within 3m and should be finished with a wire cage or perforated cover.
Part M of the building regulations concerns access to and use of buildings. It requires that access is designed in a way that enables all people to use a building and its facilities. The door thresholds should be a maximum of 15mm to meet part M requirements. Continue reading Why is a level balcony threshold dangerous?→
Foul waste water is water that comes from sanitary conveniences like toilets and wash hand basins. Suitable drainage must be supplied to remove foul water from a building using the following methods;
Through an existing public sewer
Through a private sewer that then connects to a public sewer
Into a septic tank or water treatment system
Into a cesspool
Public sewer systems are the main preferred method of drainage. You have to make sure that any risks of blockage is kept to a minimum, foul air doesn’t emanate the system, the system is ventilated, blockages can be accessed and cleared. As long as the design of the system, holding capacity and pipework diameter is sufficient then issues are limited. At any point where foulwater is discharged into the system a water seal trap should be included to prevent foul air escaping. Under conditions of use, the trap should retain a minimum of 25mm of water.
Connecting drains to a sewer system
Foul drainage should be connected to a public foul or combined sewer wherever this is practicable.
For small developments connection should be made to a public sewer where this is within 30m provided that the developer has right to construct drainage on private land.
Where levels do not permit drainage by gravity a pumping installation should be provided.
For larger developments it may be economic to connect to a public sewer even where the sewer is some distance away.
It is important the drains and sewers are not damaged during any construction works.
The sewerage undertaker is responsible for maintaining a set of records detailing the location of sewers and drainage under section 199 of the Water Industry Act 1991.
Where settlement damage may occur, 100mm of flexible filling should be used to surround pipework.
If a drain or sewer is found to be less than 2m in depth, it is advised that the foundation is extended to allow the drain or sewer to pass through.
Where a drain or sewer is greater than 2m in depth any foundation work above it should be formed as a lintel that spans over the drainage pipework with a minimum of 1.5metres span either side for pipework.
Plans for a £4.2bn “super sewer” under London have been given the go ahead by the government, it has started in 2016 to 2023. The city’s current Victorian drainage system cannot cope. It will run from Acton to Abbey Mills in East London and has a capacity of 1.25million cubic metres. Thames Water are adding £80 a year to customer bills because of it. Current systems overflow on a weekly basis, flushing 39 million tonnes of raw sewage straight into the Thames each year. During the 19th Century, the river Thames was an open sewer, which contributed towards the cholera epidemic. Joseph Bazalgette was the chief civil engineer who was responsible for carrying the development and construction of London’s modern sewage system.
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