You can extend a house in Wimbledon, but you will need permission for most of it. There are hundreds of listed buildings. Dozens of conservation areas. Clay underneath all of it. Plenty of neighbours manage to build anyway, and every one of them filed the paperwork first.
Historic England lists 268 buildings within the area's boundary box, one at Grade I, 11 at Grade II* and 256 at Grade II. Listing covers the whole building, inside and out, so changing a listed home, including its windows, internal walls or fireplaces, needs listed building consent on top of any planning permission. Most of these are Grade II, the most common grade, and Grade II still means the council looks at the plans for a kitchen with the care other places save for a cathedral.
The box takes in 40 conservation areas, among them Wimbledon North, Wimbledon West, Merton Hall Road and John Innes (Merton Park). Inside one, works that would elsewhere count as permitted development often need a planning application, demolition needs consent, and the council judges new work by whether it preserves the character of the area. John Lambert drafted the Instrument of Government, the written constitution of the Protectorate, in Wimbledon, and the borough has gone on writing rules for its streets ever since.
There are 2 scheduled monuments in the boundary box, the strictest tier of protection, which matters mostly to land right beside one. Caesar's Camp on Wimbledon Common has stood since the Iron Age, and nobody has been allowed to extend that either.
People do build here anyway. Merton received 3,394 planning applications covering the area between March 2024 and June 2026, and 1,255 of them came in the last twelve months. That is a lot of loft conversions, rear extensions and replacement windows going through the system. "Potential to extend, subject to planning" is a common line on sale particulars here, and most of its meaning sits in the brackets.
The ground sets its own conditions. The British Geological Survey rates shrink-swell clay at class 3 across the area, and every postcode reaches that class. Clay soils swell when wet and shrink in dry summers, so an extension here usually needs deeper foundations than on firmer ground, and trees nearby make that worse. A structural engineer should look at the foundation design early, while the drawings can still change without costing much.
Historic England's Heritage at Risk register includes 11 listed buildings in the area. These are buildings in poor condition. Repairs to them may qualify for grant support and will get close scrutiny from the council, which matters a great deal to whoever owns one and hardly at all to the people buying the house next door.
In practice, an ordinary house outside a conservation area may be able to do a modest rear extension or loft conversion under permitted development, while a listed house or one inside any of the 40 conservation areas will usually need full consent for the same work. Check Merton's conservation area maps for the exact house, and ask the council in writing whether permitted development rights still apply to it.
Freedom to alter a home is poor in Wimbledon. You can build, but on the council's terms, with an application, drawings and a wait for the answer.