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Garden room or extension: which is right for you?

Both add space to your home, but in very different ways. Here's how they compare on cost, rules, disruption and everyday use.

Updated 22 October 2026

A glazed room with a timber deck and wicker chairs beside a house

The short answer: a garden room is usually cheaper per square metre, much quicker to build and far less disruptive. An extension adds space to the house itself, connects directly to your living areas and almost always needs building regulations approval. Choose a garden room for a separate space to work, train or get away; choose an extension if you need a bigger kitchen or living area.

Side by side

	Garden room	Single-storey extension
Typical cost per m²	£1,200 to £2,500 installed¹	£1,800 to £3,000²
Planning permission	Usually not needed within outbuilding limits³	Rear extensions up to 3m (attached house) or 4m (detached) are usually permitted development; deeper ones need prior approval or permission⁴
Building regulations	Often exempt under 15m², or under 30m² and 1m from the boundary⁵	Almost always needed
Disruption	Built in the garden; the house carries on as normal	The house becomes a building site for a while
Connection to the house	Separate, which is the point for many people	Part of the house

A small modern garden room with glass doors at the end of a fenced garden — A garden room sits apart from the house, so work and home stay separate.

When a garden room is the better choice

You want a separate space to work, create or train, with a door to close at the end of the day.
You want to avoid planning applications, long builds and living with builders in the house.
You have a garden with room to spare, and good access for materials.

When an extension makes more sense

You need more kitchen, dining or living space inside the house.
The extra room needs to connect to the rest of the home, for example for an older relative or young children.
Your garden is small, and you'd rather give up some garden for more house.

A table set for dining beside tall glazed doors onto a garden — An extension with tall glazed doors makes the garden part of the room.

The extension rules in brief

In England, a single-storey rear extension of up to 3m on an attached house, or 4m on a detached house, is usually permitted development. Under a prior notification scheme, you can go up to 6m or 8m respectively: you tell the council, neighbours have 21 days to comment, and the council has 42 days to decide.⁴ Conservation areas and other protected land have tighter rules, so check with your council.

What about a conservatory or orangery?

A conservatory sits between the two: attached to the house but lighter and cheaper than a full extension. The trade-off is comfort, as glass roofs make conservatories hot in summer and cold in winter unless they're well specified. A garden room with good insulation is usually more comfortable all year.

Questions people ask

Is a garden room cheaper than an extension?

Usually, yes. Installed garden rooms typically cost £1,200 to £2,500 per m², against £1,800 to £3,000 per m² for a single-storey extension.¹²

Does an extension need building regulations approval?

Almost always. Garden rooms are often exempt if they're small enough and don't have sleeping accommodation.⁵

Related guides

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

Garden room costsPrices by size, with a calculator.

A garden path leading to a small building at the bottom of the garden

Planning permissionThe outbuilding rules.

A pale green garden building with a chair and a cat on the lawn

Is a garden room worth it?What owners wish they'd known.

Sources

MyBuilder, Garden room cost price guide, updated 21 October 2026. UK price ranges for garden rooms, foundations, electrics, plumbing and fees.
Federation of Master Builders, Single storey extension costs: a practical guide for homeowners, March 2026.
Planning Portal (England), Outbuildings: mini guide. Permitted development limits for outbuildings.
Preston City Council, Permitted development: house extensions. Summarises the national rear extension limits and the prior notification scheme.
Planning Portal (England), Outbuildings: building regulations. When building regulations normally apply to outbuildings.