Garden rooms and outbuildings in Brentwood depend on the house. Typical homes here: Inter-war and post-war semi-detached houses in Shenfield, Hutton, Pilgrims Hatch and Brentwood town; Large detached houses on generous plots in Hutton Mount, Shenfield and Warley. Designations to check first: Green Belt; Conservation areas; Thorndon Country Park and ancient woodland. Applications are decided by Brentwood Borough Council and the Brentwood Local Plan 2016–2033.
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 Brentwood
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 Brentwood are listed below, taken from our Brentwood area page. Each one is a reason to confirm the address on Brentwood's constraints map before relying on permitted development.
- Green Belt. Most of the Brentwood district outside the built-up areas of Brentwood, Shenfield, Hutton and Ingatestone is Metropolitan Green Belt, including the villages of Doddinghurst, Kelvedon Hatch, Blackmore and West Horndon. Source
- Conservation areas. Brentwood has conservation areas covering the town centre around the High Street, parts of Shenfield, Ingatestone, Hutton and Warley, and several village centres. Source
- Thorndon Country Park and ancient woodland. Thorndon Country Park south of Brentwood, with Weald Country Park to the west, is protected open space with areas of ancient woodland and nature conservation designations. Source
- River Wid and Ingrebourne flood risk. Land alongside the River Wid around Ingatestone and Mountnessing, and along the upper Ingrebourne and its tributaries towards Warley and Pilgrims Hatch, sits in Flood Zones 2 and 3. Source
- Listed buildings. Brentwood High Street, Ingatestone, Shenfield and the villages contain listed houses, inns and churches, with Ingatestone Hall and the chapel ruins in the town centre among the best known. Source
What Brentwood planning officers look for
Brentwood officers assess householder applications against the Brentwood Local Plan 2016–2033 and national Green Belt policy. In the Green Belt the first question is whether the extension, added to anything built since the house was original, is disproportionate; officers usually measure this by floorspace and volume, and proposals over roughly a third to a half of the original tend to need a strong case. Common refusal reasons are disproportionate Green Belt additions, terracing effects from side extensions, full-width box dormers and front dormers in conservation areas. Outside conservation areas and the Green Belt, hip-to-gable and rear-dormer lofts within 50 m³ on a semi are routinely lawful and we secure a Lawful Development Certificate as proof.
Fees and timelines
Brentwood 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.
- Brentwood Borough Council: planning: the council's own constraints map, validation checklist and pre-application service.
