House Extensions in Clapham

Lambeth or Wandsworth? Check your council first

"Clapham" crosses a borough boundary. Most of SW4, including Clapham Old Town, Clapham High Street and the streets east of the Common, is in Lambeth. Much of the area people call Clapham Junction and "Between the Commons" (SW11) is in Wandsworth. The two councils have different design guidance, so the first job on any Clapham extension is confirming which one your house sits in.

Lambeth's Building Alterations and Extensions guidance sits in its Design Guide SPD, adopted in 2023. On side infills it broadly looks for single-storey additions that are subordinate to the house; on heritage assets, infills that are mostly glazed and lightweight and set back from the corner of the back addition; and a modest wall height on the boundary. If you are in Wandsworth, its Housing SPD covers rear and side extensions to terraced houses, including the effect on neighbours' light.

What permitted development allows on a Clapham terrace

Under Class A of the government's householder permitted development guidance, a side extension (which includes building out beside the back addition) must be single storey with a maximum height of 4m, no wider than half the width of the original house, have eaves no higher than 3m within 2m of the boundary, and use materials similar in appearance to the existing house. A pure side return infill that doesn't project beyond the rear wall can therefore often be permitted development.

A single-storey rear extension can go up to 3m on a terraced or semi-detached house, or up to 6m through the prior approval process, where the council notifies neighbours and has 42 days to decide. Prior approval isn't available in a conservation area. A wraparound is treated differently: where an extension fills the area between a side wall and a rear wall, both the rear and side limits apply, so most wraparounds need a householder application. Our guide to 6m rear extensions and prior approval covers the process.

Clapham's conservation areas

In a conservation area, side extensions aren't permitted development at all, and neither are rear extensions of more than one storey or cladding. That affects a lot of Clapham. Lambeth has 62 conservation areas; the main ones in Clapham are Clapham (CA1), covering the Old Town and much of the area around the Common, Rectory Grove (CA2), Clapham Park Road / Northbourne Road (CA17) and Sibella Road (CA58). Clapham Common itself is designated by both Lambeth and Wandsworth, and Wandsworth has Article 4 Directions in some nearby conservation areas, such as Shaftesbury Park off Lavender Hill.

Our Clapham side return planning guide goes through the Lambeth and Wandsworth rules in more detail, including the Party Wall Act notices and drainage questions that come up on almost every side return.

Certificates and application fees

Even when a scheme looks like permitted development, a Lawful Development Certificate gives you proof for a buyer's solicitor later. From April 2026 it costs £274, against £548 for a householder application. In a London Planning Datahub pull we ran on 2 October 2026, Lambeth refused 31 of 198 decided LDC applications, roughly one in six, so the drawings need to be accurate before they go in.

Our Clapham project

The Clapham job we can show you is our Clapham kitchen extension and flat refurbishment: a ground-floor kitchen extension in a two-bedroom flat, with the layout reworked throughout, new bathrooms and landscaping. The owners lived at home while the work went on. Because flats have no householder permitted development rights, an extension to a flat goes through a planning application.

For side returns on houses, the closest comparison is our Earlsfield side-return kitchen extension: a 200 sq ft addition with bi-fold doors and underfloor heating. Our Wandsworth rear kitchen extension added about 350 sq ft, with a large rooflight and structural glazing.