Garden rooms and outbuildings in Merton depend on the house. Typical homes here: Victorian terraces in Colliers Wood, South Wimbledon, Mitcham and around Haydons Road; Edwardian houses in Wimbledon Park, Raynes Park and West Wimbledon. Designations to check first: Conservation areas; Article 4 directions; River Wandle flood zones. Applications are decided by London Borough of Merton and the Merton Local Plan.
The permitted development rules for garden rooms and outbuildings
An outbuilding is permitted development on a house if it is single storey, no higher than 2.5 m where it comes within 2 m of a boundary, otherwise no higher than 4 m with a dual-pitched roof or 3 m with any other roof, sits behind the front wall of the house, covers together with other outbuildings no more than half the land around the original house, and is used for purposes incidental to the house rather than as a bedroom or self-contained flat.
Anything used for sleeping or as a separate dwelling needs planning permission regardless of size. Flats have no permitted development rights for outbuildings, and listed buildings need listed building consent.
What changes in Merton
In a conservation area an outbuilding is still permitted development behind the house, but not to the side of it, and the same height limits apply.
The local constraints that most often decide the route in Merton are listed below, taken from our Merton area page. Each one is a reason to confirm the address on Merton's constraints map before relying on permitted development.
- Conservation areas. Merton has numerous conservation areas, concentrated in Wimbledon Village, Wimbledon Park, Merton Park, Mitcham Cricket Green and along the Wandle. Source
- Article 4 directions. Several Merton conservation areas, including Merton Park and parts of Wimbledon, are understood to carry Article 4 directions removing permitted development for front alterations, windows and boundary treatments.
- River Wandle flood zones. The Wandle runs through Mitcham, Colliers Wood, Merton Abbey and Wandsworth-bound Earlsfield. Source
- Metropolitan Open Land and Green Belt. Wimbledon Common, Wimbledon Park, Mitcham Common, Morden Hall Park and Cannizaro Park are Metropolitan Open Land, and the borough's south-western edge includes Green Belt.
- Listed buildings and Wimbledon Village character. Wimbledon Village, Merton Park and Mitcham Cricket Green contain many listed buildings and locally listed houses.
What Merton planning officers look for
Merton's officers follow the London-wide conventions for householder extensions, and refusals most often cite excessive depth beyond neighbouring precedent, breach of the 45-degree rule or bulky roof extensions. Pre-application advice is available for a fee.
Fees and timelines
Merton decides a householder application or a Lawful Development Certificate within 8 weeks of validation. The council fee is £528 for a householder application and £264 for a Lawful Development Certificate (England, from 1 April 2025; verify before applying).
Our own fee is fixed once quoted. The quote tool gives an indicative figure in minutes and a written quote follows within 24 hours.
Primary sources
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2: the permitted development limits quoted above.
- Planning Portal: do you need permission: the national guidance and the application service every council accepts.
- London Borough of Merton: planning: the council's own constraints map, validation checklist and pre-application service.
