Sustainable Drainage

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It has been estimated by DEFRA that significantly less than 1% of public sewers are being renovated or replaced each year. If that rate of replacement is continued, it will take approximately 800 years before a new pipeline laid today can be expected to be replaced. No product carries a certificate to say that it will last 800 years. Most will claim a Design Life of between 50 and 125 years. This does not mean that a pipe product will cease to work efficiently at the end of this time because its service life may be very different.

Design life is usually the period over which an asset’s depreciation is calculated. Design life should not be confused with service life, which is the length of time a component can be expected to perform before its performance falls below the original design requirements without requiring renovation or replacement. A major advantage of precast concrete drainage systems is that they have a proven long service life, typically in excess of 120 years. This 120 year “reference service life” is a requirement for infrastructure design and asset management assessment standards such as PAS 2080 Carbon Management in Infrastructure and Series 1700 of the Specification for Highway Works in England (NG 1704).

In the UK some soils are more aggressive to pipes than others. As a safeguard precast concrete is manufactured using Design Chemical Class 4 concrete to achieve a working life of 100 years in soils with an Aggressive Chemical Environment for Concrete class AC-4, without the need for additional protective measures.

However, where a sewer, drain or other component within the system is liable to carry: a rising main discharge; septic sewage; untreated or corrosive trade effluents; and in situations without adequate ventilation, then additional protective measures should be considered to achieve a design life of, say, 120 years.

BPDA has an extensive library of useful information and guidance publications for designers, installers and asset owners. They are available to download free of charge from the BPDA’s website. The site also holds a comprehensive and searchable FAQ section and an online enquiry facility; go to

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