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Garden rooms in Hertfordshire

Updated 22 October 2026

A small timber cabin with a pointed roof on a striped lawn

The short answer: most garden rooms in Hertfordshire don't need planning permission under the national rules. The things to check are the Chilterns National Landscape, conservation areas, and a few Article 4 directions, such as in Bishop's Stortford and St Albans.

Planning permission in Hertfordshire

Garden rooms count as outbuildings. Most can be built without planning permission if they sit behind the front of the house, have eaves no higher than 2.5m, and together with other buildings cover no more than half the garden. If any part of the room is within 2m of a boundary, the whole building must be no more than 2.5m tall; otherwise the limit is 4m with a dual-pitched roof, or 3m for any other roof. It must be single storey, with no veranda, balcony or raised platform over 30cm.¹ In the grounds of a listed building, any garden room needs permission, and so does a room used as primary living space, such as a bedroom.² Our planning permission guide explains every rule.

Protected land in Hertfordshire

On designated land, which includes National Landscapes (the new name for Areas of Outstanding Natural Beauty) and conservation areas, you can't build a garden room to the side of the house without permission.³ In a National Landscape, national park or World Heritage Site, buildings more than 20m from the house can also cover no more than 10m² in total.¹

Chilterns National Landscape: 838km² across Bedfordshire, Buckinghamshire, Hertfordshire and Oxfordshire.⁴ Check your postcode if you live in Three Rivers, Dacorum or North Herts.
Conservation areas: East Herts has 42⁵ and St Albans 19.⁶

Article 4 directions

Some Hertfordshire towns have removed permitted development rights in their conservation areas. Bishop's Stortford has an Article 4 direction that means some minor works by householders need planning permission, though works not visible from the street are mostly unaffected.⁵ St Albans has directions covering parts of some conservation areas.⁶ If you're in one of these areas, check with the council before you order.

Green Belt

Green Belt covers most of south Hertfordshire. In 2021 it covered 81.6% of St Albans, 79% of Hertsmere and Welwyn Hatfield, and 75.7% of Three Rivers.⁷

Green Belt doesn't change the permitted development rules for garden rooms. It only matters if your room needs a full planning application, because the council will then judge it against Green Belt policy.

Which council to ask, and the 2028 change

Planning is handled by the 10 district and borough councils. In July 2026 the government announced four new councils from 1 April 2028:⁸

North West Herts: Dacorum, St Albans.
South West Herts: Hertsmere, Three Rivers, Watford.
Central Herts: Stevenage, with most of North Herts and Welwyn Hatfield.
Eastern Herts: Broxbourne, East Herts, and some wards around Royston and Cuffley.

Until then, apply to your current council.

Building regulations

Building regulations don't normally apply to a garden room under 15m² with no sleeping accommodation, or one of 15m² to 30m² with no sleeping accommodation that is at least 1m from every boundary or built mostly of non-combustible materials.⁹ Running a new electrical circuit to it is notifiable work, so use a registered electrician. See our building regulations guide.

What a garden room costs in Hertfordshire

Installed garden rooms typically cost £1,200 to £2,500 per m² across the UK¹⁰, so a 4m x 3m room usually costs £14,400 to £30,000 before extras. One industry guide puts London and the South East 15% to 25% higher¹¹, which is most likely near London. With the average home in St Albans at about £647,000¹², a garden room is a small share of a typical home's value.

Questions people ask

Do I need planning permission for a garden room in Hertfordshire?

Usually not, if it meets the national size and height limits. Check for the Chilterns National Landscape, conservation areas and Article 4 directions, which can tighten the rules.

Does Green Belt stop me building a garden room in Hertfordshire?

No. Green Belt doesn't change the permitted development rules. It only matters if your room needs a full planning application.

Which council do I apply to in Hertfordshire?

Your current district or borough council until the four new councils start in April 2028.

Related guides

A small dark timber building beside a lawn and blue hydrangeas

Other areasRules and costs in other parts of the UK.

A small modern garden room with glass doors at the end of a fenced garden

Free planning reportCheck protected land at your postcode.

A white timber garden building with French doors and a red roof

Garden room costsReal prices by size, with a calculator.

Sources

Planning Portal (England), Outbuildings: mini guide. Permitted development limits for outbuildings.
Ministry of Housing, Communities and Local Government, Permitted development rights for householders: technical guidance.
Planning Portal, Outbuildings. Designated land rules for outbuildings.
Chilterns National Landscape, Our landscape.
East Herts Council, Conservation areas.
St Albans City and District Council, Conservation areas.
CPRE Hertfordshire, Hertfordshire Green Belt statistics by district, November 2021, using government data for March 2021.
East Herts Council, Government announces four unitary authorities for Hertfordshire.
Planning Portal (England), Outbuildings: building regulations. When building regulations normally apply to outbuildings.
MyBuilder, Garden room cost price guide, updated 21 October 2026. UK price ranges for garden rooms, foundations, electrics, plumbing and fees.
BestBuilders, Garden room cost UK, updated 7 September 2026. An industry cost guide, not official data.
Office for National Statistics, Housing prices in St Albans.