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Benefits of precast drainage

Precast SuDS offer a wide range of advantages that alternative engineered/ proprietary SuDS may not be able to accommodate. The following 15 reasons were mainly prepared with underground attenuation tanks in mind. They address a wide range of functionality, sustainability, resilience and site constraint aspects:


What makes precast SuDS different is that it has a proven track record of durability and long service life. Underground precast tanks are designed with a >100 years intended working life in mind (120 years in the case of highway structures). Unlike other alternatives, there is wide range of specifications and national standards which accept such long service life for concrete structures. Such proven track record cannot be found in many other lightweight alternatives.

Whole life cost (Totex)

On a whole life cost basis, precast SuDS are always cheaper as they live longer and get stronger over time and their serviceability is not limited by the amount of silt that may accumulate inside them as the units are 100% accessible. Looking at the cost over the lifetime of a development (100 years), precast SuDS and attenuation tanks will always cost less.

Structural integrity

Precast SuDS are designed to proven standards (BS 9295 and Eurocodes) and would account for a wide range of loads and forces, including lateral loads and braking/acceleration forces. Concrete gets stronger over time and its compressive strength or stiffness should not deteriorate and collapse.

Shallower cover depths

Different precast attenuation tank solutions can be installed with a very low cover depth even with traffic at ground level. There is no need for deep covers to help the units resist floatation.

Smaller land footprint

Precast attenuation tanks and other SuDS solutions take very little site footprint, compared to other alternatives, as the units can be installed deeper, and at shallower depths.

Accessibility for maintenance

Precast SuDS and attenuation tanks are usually 100% accessible for cleaning and maintenance. This is also one of the reasons why any ‘design life’ specified for the units is more achievable, compared to other alternatives, as its serviceability and function is not limited by silt accumulating in inaccessible parts of an attenuation tank.

Resistance to water jetting and cleaning

Precast SuDS can be easily cleaned with high-pressure water jetting using pressures reaching 4,000 psi, which is within the limits usually recommended by some contractors to remove FOG, fatbergs and other elements (3,000 – 4,000 psi).

Resistance to fire

Precast attenuation tanks are resistant to extreme heat and fires. In cases of open car parks’ fire, which are common in warm dry weather, the risk of collapse due to extreme heat, or fire spreading to the underground tank through fuel from burning cars’ tanks, is minimal as concrete does not burn.

Resistance to rodent attack

Precast attenuation tanks have solid reinforced concrete walls which resist any rodent attacks. The likelihood of damage due rodent attack, tree roots, or any other reason is low.

Can work with different ground conditions

Precast attenuation tanks and SuDS solutions can be installed in different grounds (including clay grounds) and would not be affected by fluctuations in the water table as the units do not float.

Can be installed between existing structures

It is structurally safe to install a precast attenuation tank right next to buildings, roads and other structures. Precast SuDS have been installed in the most challenging locations in the past without any concerns over integrity.

Resistance to weather conditions during installation

Precast attenuation tanks and SuDS can be installed under different weather conditions (e.g. rain, sunshine, etc). Unlike lightweight attenuation systems, the probability of floatation due to rainwater in the trench, or damage due to exposure to direct sunlight or heat, is nil.

Can be installed using existing machinery on site (excavators)

A precast attenuation tank made of concrete pipes is likely to be installed using the excavators available on site. There is no need for any special lifting machinery in such case. The installation process can be completed in a significantly short time if a pipe lifter is used.

Carbon footprint

Despite being significantly heavier in terms of mass, a precast attenuation tank, manufactured using DC4 concrete, is likely to have a significantly lower carbon footprint compared to an equivalent system made of HDPE pipes. More information on this can be found here.

Inert, with no concern over legacy additives

Precast SuDS are inert and would not pose a concern in terms of leaching harmful chemicals and substances of very high concern (SVHC). This is important to highlight as currently not all products' standards seem to include clear restrictions on materials with legacy additives with SVHC content (such as recycled uPVC). Recycled uPVC could have phased-out lead and cadmium stabiliser content which is no longer allowed in virgin uPVC products. With precast SuDS, developers are assured that such concern would not exist.

Resists lateral loads

Designed to resist lateral loads. A fire engine or HGV can brake multiple times over concrete tanks and SuDS components, years after installation, without concerns over collapse.