Attenuation tank installer in Manchester

An attenuation tank installer for Manchester sites

Most new building in Manchester goes onto land that has been built on before: former mills and yards in Ancoats and Collyhurst, infill plots in Salford and Trafford, surface car parks turned into apartment blocks. Planning conditions on those sites nearly always cap how fast surface water can leave, and an attenuation tank under the car park or courtyard is how the drainage design meets that cap.

We're the installer. Your drainage engineer works out the tank size and the outflow limit, your groundworker digs and forms the hole, and we build the tank inside it: fleece, membrane, crates, connections and testing. We don't dig and we don't redesign the scheme. One named team takes responsibility for the part that has to hold water for decades.

Why Manchester tanks have to hold their volume

Greater Manchester drains to the Irwell, the Mersey and the Medlock, and much of the older city still runs on combined sewers. Discharge rates agreed at planning are often low as a result, and the tank behind them has to deliver the volume on the drawing. A tank that leaks loses storage. A tank that lets groundwater in is already part-full when the storm arrives.

The rules behind it are national: the Flood and Water Management Act 2010, the NPPF and Approved Document H, with the 2025 national SuDS standards now setting out how storage and flow control should work on major schemes. Your engineer designs to those. Our job is to make sure what gets buried matches what was approved.

How we build an attenuation tank on a city plot

On tight city-centre plots the tank usually goes in between other trades, and the excavation can't stay open for long. We plan crate deliveries and welding so the tank is closed and ready for backfill as soon as it can be.

• We check the formation your groundworker has dug before we start: level, clean and blinded where the ground needs it.
• 300gsm protective fleece goes down first, then an impermeable membrane cut to the tank's shape.
• Every seam is heat-welded with calibrated equipment. We never tape a joint.
• Crates go in layer by layer, 95–97% void, until the block matches the drawing's storage volume and load rating.
• Inlets, outlets and the flow control are sealed through the wrap.
• We weld a test piece, log the result, and only then hand the tank back for backfill.

Supply and install, or install only

Crates, fleece and membrane can all come from us, matched to the drainage design, or we'll fit a system you've already bought. We fit whichever crate the engineer has specified; the loading class, depth of cover and volume matter more than the brand. If anything about supplied materials affects the weld count or the warranty, we tell you before we start.

At handover you get the weld test record, a set of as-built details and the QA sign-off paperwork: what building control, an adopting water company and a warranty provider will ask to see.