Garden rooms and outbuildings in St Albans depend on the house. Typical homes here: Georgian and Victorian townhouses and cottages in the St Albans city centre conservation area, including Fishpool Street, Holywell Hill and St Michael's; Edwardian and inter-war semi-detached houses and terraces in Fleetville, Bernards Heath and Marshalswick. Designations to check first: St Albans Conservation Area; Metropolitan Green Belt; Harpenden conservation areas. Applications are decided by St Albans City and District Council and the St Albans District Local Plan Review 1994 (saved policies) and emerging St Albans Local Plan 2041.
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 St Albans
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 St Albans are listed below, taken from our St Albans area page. Each one is a reason to confirm the address on St Albans' constraints map before relying on permitted development.
- St Albans Conservation Area. The St Albans Conservation Area is one of the largest in the country, covering the city centre, St Michael's, Fishpool Street, Holywell Hill and the streets around the Cathedral, with a high concentration of listed buildings. Source
- Metropolitan Green Belt. Most of the district outside the built-up areas of St Albans, Harpenden and the villages is Metropolitan Green Belt. Source
- Harpenden conservation areas. Harpenden has several conservation areas covering the town centre, the common and surrounding residential streets, and the district also has designated areas in Redbourn, Wheathampstead and other villages. Source
- River Ver and River Colne flood risk. Land alongside the River Ver through the city, Verulamium Park, Park Street and Redbourn, and the River Colne around London Colney, sits in Flood Zones 2 and 3. Source
- Listed buildings. The city centre, St Michael's, Fishpool Street and the village cores of Redbourn and Wheathampstead contain a very high number of listed buildings. Source
What St Albans planning officers look for
In the conservation areas they expect traditional materials, subordinate dormers on rear slopes only and no loss of historic fabric. In the Green Belt they check the size of the extension against the original house and resist large outbuildings. Common refusal reasons are full-width box dormers, side extensions that create a terracing effect and disproportionate Green Belt extensions. 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.
Fees and timelines
St Albans 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.
- St Albans City and District Council: planning: the council's own constraints map, validation checklist and pre-application service.
