Two-storey extensions in Watford depend on the house. Typical homes here: Edwardian and inter-war semi-detached houses and terraces in Callowland, Watford Fields, Holywell and around the town centre; Large inter-war detached houses on the Cassiobury Estate. Designations to check first: Conservation areas; Article 4 direction on HMOs; Cassiobury Park and Whippendell Woods edges. Applications are decided by Watford Borough Council and the Watford Local Plan 2021–2038.
The permitted development rules for two-storey extensions
A two-storey rear extension is permitted development only within tight limits: no more than 3 m deep, at least 7 m from the rear boundary, no higher than the existing house, eaves matching the existing eaves, materials similar in appearance, and any upper-floor side window obscure-glazed and non-opening below 1.7 m.
Most two-storey extensions exceed one of those limits, most often the 7 m rear boundary rule on London plots, so the usual route is a householder planning application. Flats have no permitted development rights.
What changes in Watford
Extensions of more than one storey are not permitted development in a conservation area, so planning permission is always needed there.
The local constraints that most often decide the route in Watford are listed below, taken from our Watford area page. Each one is a reason to confirm the address on Watford's constraints map before relying on permitted development.
- Conservation areas. Watford's conservation areas include Cassiobury, Nascot, Estcourt and Oxhey Village, as well as parts of the town centre and High Street. Source
- Article 4 direction on HMOs. We understand Watford Borough Council has used an Article 4 direction to remove permitted development for converting a house into a small house in multiple occupation (C3 to C4), so HMO conversions normally need planning permission. Source
- Cassiobury Park and Whippendell Woods edges. Houses backing onto Cassiobury Park, the Grand Union Canal corridor and the edge of Whippendell Woods sit against protected open space, often with tree preservation orders and some Green Belt land. Source
- River Colne and Grand Union Canal flood risk. Land alongside the River Colne and the Grand Union Canal on the west and south of the town, including parts of Cassiobury, Holywell and Oxhey, sits in Flood Zones 2 and 3. Source
- Listed buildings. The High Street, St Mary's churchyard, Nascot and the Cassiobury area contain listed houses, almshouses and churches. Source
What Watford planning officers look for
On the Edwardian and inter-war semis that make up much of the town they tend to look for two-storey side extensions set back from the front wall and below the main ridge, with a gap kept to the side boundary so the pair does not read as a terrace; rear extensions that pass the 45-degree test to the neighbour's nearest habitable window; and dormers that are subordinate, set back from the eaves and clad in matching tile. Common refusal reasons are full-width box dormers, side extensions that create a terracing effect and front dormers in conservation areas. Outside conservation areas, 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. Watford offers a paid pre-application service.
Fees and timelines
Watford 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.
- Watford Borough Council: planning: the council's own constraints map, validation checklist and pre-application service.
