Kensington and Chelsea SuDS requirements for basements

When RBKC expects a drainage statement, what the drawings must show, and the extra detail needed for basement schemes.

Trails Research·Updated 2026-09-03·10 min read
Council guidance checked 3 September 2026

The short version

RBKC asks for a drainage statement for basements and for small schemes that alter the ground or the way a site drains. That includes ground-floor extensions, outbuildings, hardstanding and some landscaping. A change of use or upper-floor alteration will not normally need the small-scheme statement if there are no relevant external works.

Small-scheme trigger
Basements and ground-level external works
Core evidence
Annotated surfaces and proposed SuDS layout
Basement gardens
At least 1 metre of permeable soil

Use this as a starting point. Check the current validation list and the particular flood and drainage constraints on your site before submitting.

Start by confirming what the council asks for and which flood-risk tests apply to the site. Then use the document list and technical checks to set the scope. Further down, we look at the drainage conditions and refusal reasons found in the borough's decision notices.

When is a drainage strategy or FRA needed?

Project situationWhat to doStatus
Basement developmentProvide a drainage statement and show the proposed SuDS response as part of the basement design. Required
Lower- or ground-floor extension or outbuildingInclude the council’s small-scheme drainage information if the work changes runoff or impermeable area. Required
New hardstanding or consented landscaping worksShow the change in permeable area and how runoff will be managed. Required
Pure change of use, fenestration or upper-level worksThe small-scale drainage statement is normally exempt where there are no relevant external works. Check for this site
Major development or a flood-risk constraintCheck the validation, FRA and London SuDS Proforma requirements separately; the small-scale note is not the full test. Check for this site
Application documents

What to send with the application

Prepare these first

  • A drainage statement covering the points in the RBKC guidance
  • Annotated existing and proposed plans showing permeable and impermeable areas
  • The location, dimensions and connections of the proposed SuDS measures
  • Drainage-hierarchy justification and long-term maintenance arrangements

Add these if relevant

  • Basement details demonstrating the depth and finish of soil above the structure
  • Flood risk assessment and wider drainage calculations where site risk or development scale triggers them
  • Supporting ground or connection evidence where the selected discharge route depends on it

What the drawings and calculations need to show

1

Compare existing and proposed surfaces

Submit annotated plans identifying impermeable and permeable areas before and after development.

2

Draw the proposed SuDS

Show the location and dimensions of each measure and how the drainage network connects.

3

Work through the drainage hierarchy

Manage runoff as close to its source as possible and explain why any higher-priority discharge option is not practicable.

4

Resolve basement and maintenance details

For a basement roof to count as permeable, the council expects at least 1 metre of soil with grass, planting or another permeable finish. State who will inspect and maintain every SuDS feature.

Example scope

Basement beneath part of a rear garden

A domestic basement extends below landscaped garden and changes the way rainfall reaches the ground.

  1. Map the existing and proposed permeable areas rather than describing the garden generically.
  2. Show the basement outline, finished levels, SuDS locations and drainage connections on coordinated plans.
  3. Only count the roof of the basement as permeable where the landscape build-up provides the required soil depth and permeable finish.
  4. Explain exceedance, inspection access and who will maintain the measures after occupation.

This example shows how the submission might be assembled. It is not a drainage design. The final scope depends on the site and the proposal.

Official forms and guidance

These links were checked 3 September 2026. Forms and validation requirements do change, so check the council website again before issuing the application.

What we found in the decision notices
From … planning decision notices from Kensington and Chelsea, refreshed daily

Observed planning-condition data

… of the approvals read carry a drainage or SuDS condition
… of those conditions must be discharged before work starts

What the drainage conditions actually ask for

The theme breakdown appears once enough drainage-conditioned approvals have been read to report it reliably.

Allow for discharge before agreeing a start date

There are not yet enough records to publish a reliable borough figure. Check the exact wording on the permission before agreeing the programme.

  1. Copy the condition into a schedule and list the evidence that answers each clause.
  2. Check that the calculations, drawings, specifications and maintenance plan use the same assumptions and references.
  3. For a pre-commencement condition, secure the written discharge before starting any work covered by the restriction.
  4. Where the condition asks for verification, keep site photographs, installation records and as-built information.

Understand the programme effect of a pre-commencement condition .

Reasons drainage submissions are refused

We have not read enough refusals in Kensington and Chelsea to publish a useful local breakdown. The London-wide analysis is available for wider context.

Projects attracting these conditions

There are not yet enough records to publish a reliable project-type breakdown.

About the data

The observed figures are computed from the planning decision notices from Kensington and Chelsea and are recalculated as we read more. We do not publish a rate when its sample is too small. This is not a complete record of every decision made by the authority, and it cannot tell you whether a document will be accepted for a particular site. Only aggregate figures appear here. See the full methodology or the London-wide picture.

Working in another borough? Compare drainage conditions and refusal patterns across London, then look at the individual schemes and project teams behind the figures.

See how Trails works for consultants →

Frequently asked questions

When does RBKC require a drainage statement?
RBKC’s small-scale guidance covers basements, lower- and ground-floor extensions, outbuildings, landscaping requiring permission and new hardstanding. Pure changes of use without external alterations, fenestration changes and upper-floor or roof extensions are normally exempt from that small-scale requirement.
What must an RBKC drainage statement show?
Provide annotated existing and proposed plans showing impermeable and permeable surfaces, the location and dimensions of each SuDS measure and drainage connections. Explain how the drainage hierarchy was applied and set out the maintenance activities and responsible party.
When can landscaping over an RBKC basement count as permeable?
RBKC says there should be at least 1 metre of soil above the basement for the area to count as permeable, and it must be finished with grass, vegetation or another permeable surface. The drainage design should still address levels, flow paths and long-term maintenance.

About this data

This article reports patterns in UK planning decision notices that Trails reads across London local planning authorities, recomputed daily. Every figure carries its own sample, and the London page shows how much of each borough's decisions we have read.

→ The full London flood & drainage picture→ Methodology and sources

About Trails

Trails reads London planning decision notices every morning and shows flood and drainage consultants which schemes have just picked up a drainage condition, which discharge submissions were refused, and the architect behind each one.

See how Trails works for consultants →