A recent revision of precast drainage standard, BS 5911, offers more certainty about the intended working life of precast concrete SuDS solution.

BSI has published a revised edition of BS 5911-1, specification standard for unreinforced and reinforced concrete pipes, with a number of amendments which will improve how specifiers understand the durability of precast drainage systems, including precast SuDS components.

Durability is one of the main characteristics considered in the design of stormwater storage and attenuation tanks and other SuDS systems. There is no single agreed service life period for SuDS infrastructure. But SuDS solutions would be expected to perform effectively and with robust structural integrity throughout the life of the housing estate, retail or commercial development it serves. CIRIA’s Benefits of SuDS Tool (BeST) suggests a 100 years’ service life for a SuDS scheme. Many industry specifications, such as highway standards and PAS 2080, target a minimum design life of 120 years for infrastructure assets.

Defra’s SuDS Non-Statutory Technical Standards require SuDS solutions to be structurally robust throughout the design life of the development. For attenuation tanks, structural design requirements, and its associated working life, are specified in a number of ways: For example, Box culverts are designed to Eurocodes (EN 1992) with a clear reference to an intended working life of 100 years. Geocellular tanks are designed to CIRIA’s C737, but its design life advice can be found in testing standards EN 17152-1 or in products’ BBA certificates (usually 50 to 60 years). In the past, concrete pipeline products standards did not make any clear reference to a specific intended working life. The 100 years intended working life for concrete pipes was mainly based on reinforcement cover and exposure class design for 100 years as specified in the concrete specification standards and National Highways specification for concrete infrastructures. However, this has now changed following the update to BS 5911:

The new standard introduces a clearer justification explaining the link between specification of a DC-4 exposure class concrete mix to a 100 years’ Intended Working Life for pipes. As noted above, that link already existed in the past as all precast drainage is already specified to standards such as Special Digest 1 “Concrete in Aggressive Grounds” and BS 8500. But following the latest amendment, there is now a direct reference to a 100+ years in the pipes standard. The direct reference to a 100 years’ working life would not only help with asset management and Whole Life cost planning, but also with Design for Circular Economy, carbon footprinting and long-term performance.

The new BS 5911-1: 2021 can be purchased from the BSI website. For any further information on the new standard please contact email@precastdrainage.co.uk