A drainage strategy report costs from £570 at Fixed Fee Plans. It sets out where the foul and surface water from your new homes will go, how much there will be, and how the scheme follows the London Plan's drainage hierarchy, in the form your council asks for. It is a desk report; if the site needs an engineered design, such as a sized soakaway or an attenuation tank, we say so and that is quoted separately.
It is the new-home version of drainage. For an extension, the shorter SuDS statement usually does the job.
When does a council ask for a drainage strategy?
For new homes, more and more often. Merton asks for one with all new dwellings and major developments, in every flood zone, under Policy F15.8 of its 2024 Local Plan. Other councils ask for it with majors or in flood zones only. We read your council's plan and list for your scheme before quoting, and if it is not required we tell you.
What is the London Plan drainage hierarchy?
Six ways to deal with rainwater, in order of preference, from Policy SI 13 of the London Plan: use it as a resource, such as rainwater harvesting; let it soak into the ground close to where it falls; hold it in green features such as green roofs and rain gardens; discharge it to a watercourse; then a surface water sewer; and only last a combined sewer. The plan also asks schemes to aim for greenfield run-off rates.
The strategy works down that list for your site and records why each option is used or ruled out. In much of inner London the answer stops at attenuation and a controlled discharge, and saying so plainly is part of the job.
What do London councils add?
Their own numbers. Southwark asks for a 40% allowance for climate change in the design calculations, and a SuDS proforma on major schemes. Kensington and Chelsea asks development to reduce the rate and volume of run-off into the combined sewer. Waltham Forest, where greenfield rates cannot be reached, secures a payment in lieu. The strategy uses your council's figures, not a national default.
What happens after the strategy?
It goes with your application, and the council may attach a drainage condition that needs details later; our discharge of conditions service handles that. If the site is in a flood zone, the flood risk assessment and, for new homes, the sequential test usually go in alongside it. Our fee is from £570 for a desk strategy for a small scheme; a larger site is quoted in writing.
Frequently asked questions
What is the difference between a drainage strategy and a SuDS statement?
A drainage strategy covers foul and surface water for new homes. A SuDS statement is the shorter document for an extension or a single home, focused on rainwater from the new roof and paving.
Does a drainage strategy include soakaway design?
No. It says whether infiltration is likely to work and where. Sizing a soakaway needs ground testing and an engineer's design, which is quoted separately.
Will Thames Water need to approve the connection?
A new connection to the public sewer needs an application to the sewerage undertaker. The strategy notes where one is needed.
