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Garden rooms in Dorset

Updated 22 October 2026

A shepherd's hut among trees

The short answer: much of Dorset is protected. The Dorset National Landscape covers about 42% of the county1, and Cranborne Chase adds more in the north2. On that land you can't build to the side of the house, and buildings more than 20m from the house are limited to 10m² in total. Near the heaths, a garden room used as a separate home is especially unlikely to be allowed.

Planning permission in Dorset

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.3 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.4 Our planning permission guide explains every rule.

Protected land in Dorset

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.5 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.3

Dorset Council says the conservation of natural beauty is given "great weight" in planning decisions in the National Landscapes2, so if your room does need permission, design and materials matter.

Article 4 directions

Dorset Council lists 57 Article 4 directions, including ones for Dorchester, Swanage and Wareham conservation areas.8 The Dorchester one, for example, covers only boundary walls, gates and fences. Check the one for your area before you order.

The Dorset heathlands rule

This one is specific to Dorset. Within 400m of protected heathland, no new home is allowed on the same site, and an annexe is only acceptable if it stays part of the main house.9 Between 400m and 5km, new homes must avoid adding pressure on the heaths.10 An ordinary garden office or gym isn't a new home, but a garden room someone will live in could fall foul of this, so ask the council first.

Which council to ask

Since April 2019 Dorset has had two councils: Dorset Council, and Bournemouth, Christchurch and Poole (BCP) Council.11

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.12 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 Dorset

Installed garden rooms typically cost £1,200 to £2,500 per m² across the UK13, so a 4m x 3m room usually costs £14,400 to £30,000 before extras. One quote site puts a mid-range 12m² garden office in the South West at about £18,000 fully installed.14 Average home prices in August 2026 were £328,589 in the Dorset Council area and £310,176 in BCP.15

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Questions people ask

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

Often not, but much of Dorset is a National Landscape, where you can't build to the side of the house and buildings more than 20m from the house are limited to 10m² in total. Check your postcode with our free planning report.

What is the Dorset heathlands rule?

Within 400m of protected heathland, no new home is allowed on the same site, and an annexe must stay part of the main house. It matters most if someone will live in the garden room.

Which council do I apply to in Dorset?

Dorset Council, or BCP Council if you live in Bournemouth, Christchurch or Poole.

Related guides

A small dark timber building beside a lawn and blue hydrangeasOther areasRules and costs in other parts of the UK. A small modern garden room with glass doors at the end of a fenced gardenFree planning reportCheck protected land at your postcode. A white timber garden building with French doors and a red roofGarden room costsReal prices by size, with a calculator.

Sources

  1. Dorset National Landscape, Management plan 2026-31, chapter 2.
  2. Dorset Council, Areas of Outstanding Natural Beauty.
  3. Planning Portal (England), Outbuildings: mini guide. Permitted development limits for outbuildings.
  4. Ministry of Housing, Communities and Local Government, Permitted development rights for householders: technical guidance.
  5. Planning Portal, Outbuildings. Designated land rules for outbuildings.
  6. UK National Commission for UNESCO, Dorset and East Devon Coast (the Jurassic Coast).
  7. BCP Council, Conservation areas.
  8. Dorset Council, Article 4 directions.
  9. Dorset Council and BCP Council, Dorset Heathlands Planning Framework 2020-2025.
  10. Dorset Council, Dorset Heathlands Planning Framework.
  11. Public Sector Executive, New unitary authorities formally take over from Dorset's nine councils, April 2019.
  12. Planning Portal (England), Outbuildings: building regulations. When building regulations normally apply to outbuildings.
  13. MyBuilder, Garden room cost price guide, updated 21 October 2026. UK price ranges for garden rooms, foundations, electrics, plumbing and fees.
  14. Less, Garden room cost, updated April 2026. A commercial quote site; its method isn't published, so treat regional figures as indicative.
  15. HM Land Registry, UK House Price Index England: August 2026, provisional figures published 21 October 2026.