Building Regulations for Garden Rooms

What you need to comply with and when approval is required

Building regulations rules can change. Always check with Building Control before you start.

Planning permission vs building regulations

These are two separate things — and you need to think about them independently:

Planning permission

Controls whether you can build at all — size, appearance, location. Most garden rooms are covered by Permitted Development.

Building regulations

Controls how you build — structural safety, fire safety, energy efficiency, electrical safety. Applies regardless of planning permission status.

When do garden rooms need building regulations approval?

Most small garden rooms are exempt from building regulations under the "exempt buildings and work" schedule. Here is the key threshold:

The 30m² rule

A detached outbuilding under 30m² floor area is generally exempt from Building Regulations if:

It contains no sleeping accommodation
It is either: more than 1m from any boundary AND the structure is substantially non-combustible, OR it is more than 1m from any boundary
No hot water storage is provided

Important: Even if the building itself is exempt, specific types of work may still require Building Regulations approval — most notably electrical work and structural work.

Specific areas that may require approval

Electrical installation

Usually required

If you are running a new electrical circuit from your house to the garden room, this is Part P notifiable work and must be either certified by a competent person (registered electrician) or approved by Building Control before and after. You cannot legally just connect it yourself without one of these routes.

Plumbing / hot water

Depends

If you add a sink, toilet, or hot water supply, this may trigger Building Regulations. Cold water supply to a sink in an exempt building is generally fine. Hot water storage or bathroom facilities typically require notification.

✓

Structural work

Usually exempt

For standard DIY garden rooms up to 30m², structural regulations generally don't apply if the building is exempt. If you are building over 30m² or with unusual spans, you may need a structural engineer's sign-off.

✓

Thermal performance / insulation

Usually exempt

For exempt buildings, there are no mandatory U-value requirements. However, if the building is connected to the house's heating system or used as a habitable space regularly, good practice is to build to Part L standards.

Fire safety

Depends

For exempt outbuildings, fire regulations don't formally apply, but you should still install a smoke alarm and ensure exits are adequate. If within 1m of a boundary, combustible cladding materials may be restricted.

How to notify Building Control

If your work requires Building Regulations approval, you have two main options:

Full Plans Application

Submit plans before work begins. Building Control checks them and gives approval. Inspections happen during the build. Best for larger or more complex builds. Fee typically £150–£500.

Building Notice

Notify Building Control that you are starting work. An inspector visits during the build. No plan submission needed upfront. Faster but less certainty. Fee typically £100–£300.

Ready to build your garden room?

Get the complete DIY build pack — full plans, materials list, and step-by-step guides for £49.

Get the Build Pack — £49