Construction Drainage

Surface water drainage carries rainwater from roofs and hardstanding to a soakaway or main drain. We install the runs, gullies and connections to the design. Building control and water company consent may apply where we connect to the public system.

Attenuation crates store surface water and release it slowly to reduce peak flow to the drain or watercourse. They are often specified on new developments. We install attenuation systems to design with the correct storage volume and flow control.

Foul drainage carries wastewater to the main sewer or treatment system. We install foul runs and connections to the design. Connection to the public sewer usually needs water company approval and building control compliance.

New housing developments need a drainage strategy: surface water (soakaways, attenuation or main drain) and foul (connection to sewer). Planning and adoption requirements drive the design. We deliver the groundworks and drainage to the approved design.

Drainage trenches are excavated to the depth and fall specified in the design. We excavate trenches for surface water and foul runs, leave them ready for laying or lay the pipes ourselves, then backfill and reinstate.

A percolation test measures how quickly water drains into the ground. It is used to size soakaways. We do not usually carry out the test; we use the result to install the soakaway to the design. Your drainage engineer or ground investigation contractor can arrange the test.

Connecting to the public sewer usually requires approval from the water company. We deliver the groundworks and drainage up to the connection point; the water company may make the final connection or we do it under their approval. We work to the agreed design.

French drains (trenches filled with gravel and sometimes a pipe) intercept and disperse groundwater or surface water. We install French drains and land drainage to design to keep the site or building dry.

Drainage sometimes runs under a building. Build-over consent and structural support may be required. We work with the structural and drainage design to excavate, support or divert as specified so the build can proceed safely.

Rainwater harvesting collects surface water for reuse. The drainage design may include a tank, filter and connection to the building. We install the tank and associated drainage to design so the system can be connected by the M&E contractor.

Adoption means the water company takes ownership of the drainage after construction. S104 (sewer) and S38 (highway) agreements set the standard and process. We build to the adoption design and provide the documentation the water company requires.

Manholes and inspection chambers allow access for maintenance and rodding. We construct chambers to the design — brick, concrete or pre-cast — and connect the runs at the correct levels. Building control and adoption specify the type and size.

Drainage is tested (e.g. air test or water test) to prove it is watertight and has the correct fall. We carry out or coordinate testing after installation and before backfill or covering. We provide the results for building control or adoption.

Temporary drainage diverts surface water and keeps excavations dry during the build. We install temporary runs, sumps and pumps as part of enabling works. We maintain them until permanent drainage is in place or the site is handed over.

In the UK, surface water and foul drainage are usually separate. Surface water goes to soakaway, watercourse or surface water sewer; foul goes to the foul sewer. We install separate runs and connections to the design.

Deep or unstable drainage trenches may need support (timber, trench boxes or sheet pile). We excavate and support to the design so the drainage can be laid safely. We remove support and backfill in the agreed sequence.

Soakaways need to be accessible for inspection and maintenance. The design may include an inspection chamber or removable lid. We install soakaways to design with the specified access so they can be maintained.

Drainage design must coordinate with foundations, services and structure. We work with your drainage engineer and structural engineer so runs and connections are in the right place and the build sequence works. We do not design drainage; we deliver to the coordinated design.

Sustainable drainage (SuDS) aims to manage surface water close to where it falls. Soakaways, attenuation, permeable surfaces and swales are common. We install SuDS components to the design so the scheme meets planning and adoption requirements.

As-built records show where drainage was built and at what levels. They are needed for building control, adoption and future maintenance. We provide as-built for the drainage we install — drawings and levels.