Stormwater Attenuation Tank Calculator

First-pass estimate of attenuation storage volume and StormGrid module count for a lined geocellular tank. Indicative only – final sizing needs a hydraulic calculation, greenfield runoff rate and climate-change allowance to CIRIA C753.

Impermeable area drained (m²) roof / car park / yard runoff area

Design storm depth (mm) 1-in-30 to 1-in-100yr event; UK typical ~40-60 mm

Climate-change allowance uplift on rainfall intensity per Environment Agency guidance

StormGrid module height storage per module: H400 190 L, H500 237.5 L

Attenuation storage

30 m³

StormGrid modules127

Tank footprint @ 1 m deep32 m²

Get an engineer-reviewed layout and FOB quote

Method: storage = area x storm depth/1000 x climate factor. Modules = storage / module storage volume. This ignores the permitted discharge offset, which reduces required storage – a full hydraulic model to CIRIA C753 will refine it. Load class and cover depth are designed separately.