Basement Planning Application in Kensington and Chelsea: What Goes In at Submission, and the Refusal for a Missing CTMP

A basement planning application in Kensington and Chelsea needs more than drawings and a design statement. The Royal Borough's Local Plan 2024 asks for a site-specific flood risk assessment for every basement in any flood zone, a sustainable drainage (SuDS) statement and a pumped device against sewer flooding. It also asks for the construction documents: a draft Construction Traffic Management Plan (CTMP), a construction method statement, and a noise, dust and vibration report.

In July 2026 the council's Planning Applications Committee refused a mews house with a new basement in Chelsea, against the officers' recommendation, and the first reason was the missing draft CTMP. This guide sets out what RBKC expects at submission, from its policy, its decisions and Air & Flood Consultants (AFC) jobs in the borough.

Fee proposals: send the address and drawings through the enquiry form before you submit. See also AFC's basement impact assessment and London flood risk assessment services.

The RBKC policies that apply to a basement

Basements are assessed against Policy CD11 of the Kensington and Chelsea Local Plan 2024 (adopted July 2024) and the council's Basements SPD (April 2016). CD11 replaced Policy CL7 of the 2019 plan, and older decisions still use the CL7 numbering.

CD11 opens "The Council will require all basement development to:" and sets fourteen criteria, A to N. A, B and J limit the size (see the FAQ below). These decide what goes in the application:

• I: "include a sustainable drainage system (SuDS), to be retained thereafter";

• K: "ensure that traffic and construction activity do not cause unacceptable harm to pedestrian, cycle, vehicular and road safety";

• L: "ensure that construction impacts such as noise, vibration and dust are kept to acceptable levels for the duration of the works";

• M: "be designed to safeguard the structural stability of the existing building, nearby buildings and other infrastructure";

• N: "be protected from sewer flooding through the installation of a suitable pumped device".

Four other Local Plan policies sit beside CD11:

• GB11 Flood Risk: site-specific FRAs are required for development in Flood Zones 2 and 3, sites over one hectare, and "All basement development".

• GB12 Sustainable Drainage: "Development must contribute towards a reduction in the rate and volume of surface water run-off into the combined sewer network". It also asks for "green/blue roofs on all flat roofs including extensions".

• GB6 Air Quality: a dust risk assessment for dusty works such as basement excavation.

• GB18 Contaminated Land: "A preliminary risk assessment of contaminated land is required at the planning application stage" for basements and other sensitive smaller schemes.

What to submit with a basement planning application in Kensington and Chelsea

Figure 1 sets out the package, one document per row, with the policy that asks for it.

Figure 1. What RBKC needs with a basement application, by document and policy.

On drainage, the council's SuDS guidance page (last updated 21 September 2026) asks householder schemes, basements included, for a Drainage Statement:

• plans of the existing and proposed impermeable areas, and of each SuDS element;

• the drainage hierarchy followed, and the maintenance and who does it;

• how the scheme meets each of the National SuDS Standards.

A scheme with one or more new dwellings needs a full Drainage Strategy instead. London Plan Policy SI 13 sets the drainage hierarchy for London (London Plan chapter 9). AFC's SuDS strategy service covers both.

The flood risk assessment must deal with groundwater and sewer flooding as well as surface water. On an AFC job in Chelsea, the council's 2022 Strategic Flood Risk Assessment (SFRA) mapping showed groundwater rising to within 0.025 m of the surface in a 1% annual probability event, and the risk was rated high. AFC's groundwater flood risk assessment covers that part, and a construction dust risk assessment covers GB6.

The refusal: a mews basement without a draft CTMP

The application was for a replacement two-storey house with a basement storey on a small mews plot in the Chelsea Conservation Area. The site is in Flood Zone 1 and the Sloane Square Critical Drainage Area. It went in during March 2026 with an FRA and SuDS strategy, a construction method statement with a borehole investigation, and a noise, dust and vibration report. It had no draft CTMP.

The officer report of 9 July 2026 found the flood and drainage work acceptable. On the CTMP, paragraph 6.30 reads: "A draft Construction Traffic Management Plan (CTMP) has not been submitted with the application, in direct conflict with Policy CD11. However, a condition would suffice in this particular case, as recommended by the Council's Highways Officer." Officers recommended approval with a pre-commencement CTMP condition.

Figure 2. The application from submission to refusal, from the council's published reports.

The 17 objections, several about construction disruption and site access, sent the application to committee. The committee is not bound by the officers' recommendation, and on 21 July 2026 it refused permission. The first reason on the decision notice of 24 July 2026 reads:

"The applicant has failed to demonstrate, through the submission of a draft Construction Traffic Management Plan (CTMP), that the proposed development would not result in unacceptable impacts on pedestrian, cycle and vehicular safety, or cause unreasonable inconvenience to the day-to-day activities of those living, working and visiting the surrounding area. In the absence of this information, the proposal has failed to demonstrate compliance with Policy CD11 of the Kensington and Chelsea Local Plan and the adopted Basement SPD."

The second reason was design and the Chelsea Conservation Area, so the CTMP was not the only reason. It was the one a missing document created, on a scheme officers had found acceptable on every technical point.

The same committee granted other applications that evening with a CTMP condition, so a condition is possible, but not guaranteed. The decision notice also records that pre-application advice was given and "not adhered to".

Illustrative AI image; not a real site or an AFC project.

A draft CTMP answers the points in the council's standard condition: vehicle routes and numbers, site access, the call-up procedure, parking suspensions, the work programme, pedestrian protection, and a plan of any hoarding on the highway.

Critical Drainage Areas: SuDS on a fully built plot

Most basement plots in Chelsea and Kensington are small, fully hard-surfaced, and inside a Critical Drainage Area. GB12 still requires a reduction in runoff to the combined sewer. What RBKC accepts depends on the plot.

On the refused mews plot, the applicant's engineer showed that the 1 in 100-year plus 40% climate change event needed only about 3 m³ of storage. Throttling the discharge to cut the rate by 50% would have needed an orifice about 16 mm across, which would block with leaves and grit. No flow control was proposed. Infiltration was ruled out on impermeable made ground with buildings within 5 m, and green roofs, water butts and permeable paving were each discounted for stated reasons. Rain planters at the front of the house were proposed instead.

The officer accepted it (paragraph 6.33): the rain planters "would provide a proportionate reduction in surface water runoff rates commensurate with the scale of the development", secured by a condition to implement and maintain them.

On larger or fully rebuilt plots, RBKC has used a stricter pre-commencement condition. AFC prepared the FRA and SuDS strategies to discharge it for two adjoining terraced houses in Chelsea, also in the Sloane Square Critical Drainage Area. Each scheme rebuilds the house with a basement under the whole footprint. The 2024 permission asked for an analysis "to achieve a reduction of 50% of existing rates including climate change in the calculations and factoring in all flows into the sewer system including groundwater or other flows", and added "(More sustainable green SuDS should be favoured over attenuation tanks)".

Figure 3. AFC's runoff results for one of the two Chelsea houses.

Each plot is about 50 m² and 100% impermeable, on London Clay, so infiltration was ruled out. AFC's strategy used a 25 m² sedum roof and a 280 l water butt feeding the basement WC, discharging through the existing sewer connection. Peak runoff fell by 50% to 70% at every return period (Figure 3).

Illustrative AI image; not a real site or an AFC project.

On the second house, the council's flooding officer raised no objection to a five-page architect's note at application stage, and the detail went into that pre-commencement condition. The work still has to be done before the basement is dug.

Sewer flooding and the pumped device

CD11(N) and GB11 require a basement connected to the sewer to be protected "through the installation of a suitable pumped device". A sump drawn on the basement plan does not settle it.

On the refused mews scheme, the basement plans already showed a sump pump, and the officer report recorded criteria I and N as met. The addendum report put to the committee on 20 July 2026 still added condition 13: "Prior to the first occupation or use of the basement level hereby approved, the basement shall be fitted with a positively pumped device designed to remove sewer floodwater from the building, which shall be maintained and remain functional at all times thereafter." Both Chelsea permissions on AFC's job carried a pumped device condition too.

Figure 4. How a positively pumped device protects a basement from sewer surcharge (illustrative, not to scale).

The FRA should show the device, the non-return valve, and where the pumped water discharges, and the drainage drawings should match it. AFC's Chelsea reports took 94 sewer flooding incidents in the SW3 postcode area since 2000 from the council's SFRA, and rated sewer flood risk medium.

After permission: the conditions to discharge

A basement permission in RBKC arrives with pre-commencement conditions. On the refused mews scheme, officers recommended conditions for:

• the CTMP;

• a chartered civil or structural engineer for the works;

• the council's Code of Construction Practice checklist and Site Construction Management Plan;

• contamination, in four phased conditions;

• the SuDS.

Check the permission's time limit: one of the two Chelsea permissions reached AFC about 10 weeks before it lapsed, and RBKC normally takes up to 8 weeks to decide a discharge. AFC's guide to discharging a surface water drainage condition sets out the process, and the NPPF 2026 basement article the national policy.

Checklist before you submit

• FRA covering every source, with the pumped device and non-return valve.

• Drainage Statement or Strategy showing a runoff reduction.

• Draft CTMP.

• Construction method statement by a chartered engineer, with borehole results.

• Noise, dust and vibration report and dust risk assessment.

• Contamination preliminary risk assessment.

• Plans showing the CD11 size limits, and any changes pre-application advice asked for.

For a basement elsewhere in London, AFC's basement impact assessment case study in Brent shows a different council's requirements.

Do I need a flood risk assessment for a basement in Kensington and Chelsea if I'm in Flood Zone 1?

Yes. Policy GB11 requires a site-specific FRA for "All basement development", whatever the flood zone, covering groundwater and sewer flooding too. See AFC's London flood risk assessment page.

What is a Construction Traffic Management Plan and do I need one with my basement application?

A CTMP sets out how construction vehicles reach and serve the site: routes, access, vehicle numbers, parking suspensions and pedestrian protection. Submit a draft with any basement application in RBKC.

Can a basement application be refused for a missing document?

Yes. RBKC's committee refused a Chelsea basement in 2026 because no draft CTMP was submitted, although officers would have secured one by condition.

What is a positively pumped device and why does RBKC require it?

A sump and pump that lifts basement drainage to ground level and discharges it above the sewer's surcharge level, with a non-return valve. Policy CD11(N) requires one, and RBKC conditions it to be fitted before the basement is first used and kept working.

How big can my basement be in Kensington and Chelsea?

Policy CD11 limits a basement to one storey (exceptions on large sites) and to no more than 50% of each garden or open part of the site, with the rest in one area. Any part under a garden needs at least one metre of soil above it.

What SuDS does RBKC accept on a small site with no garden?

Green or blue roofs, rainwater reuse and planters. On a fully built mews plot, officers accepted front rain planters with no flow control, as the orifice needed would have been about 16 mm.

How long does RBKC take to discharge basement conditions?

Normally up to 8 weeks per discharge application. Check the permission's expiry date before you start, as the pre-commencement conditions must be discharged before work begins.

Enquiries

Air & Flood Consultants prepares flood risk assessments, SuDS strategies and dust risk assessments for basements across London. Send us your drawings before you submit and we will tell you which RBKC documents you need, through the enquiry form.