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Building Regulations for Outbuildings Over 30m²: A 2026 Guide

Bhavesh Ramburn

The 15m² Building Regulations exemption

Most detached outbuildings (garden rooms, sheds, summerhouses, home offices, and similar) under 15 square metres floor area are exempt from the Building Regulations under Schedule 2 of the Building Regulations 2010 (SI 2010/2214). The exemption applies provided:

  • The outbuilding is single-storey (not two-storey).
  • The outbuilding is detached from any other building, or separated by a fire-resisting wall.
  • The floor area does not exceed 15m².
  • The outbuilding is not used for sleeping accommodation.
  • The outbuilding does not contain any fixed combustion appliance (e.g. a log burner or gas heater) other than a normal domestic cooker or boiler in a kitchen.

A 30m² outbuilding, by contrast, does exceed the Schedule 2 exemption and requires a full Building Regulations application. The same is true for any outbuilding over 15m², any outbuilding with sleeping accommodation, and any outbuilding with a fixed combustion appliance.

The primary statute is the Building Act 1984. The technical standards are set out in the Approved Documents published by the Department for Levelling Up, Housing and Communities.

For the broader context on the Building Regulations regime, see our Building Regulations UK guide and our Building Control in the UK guide.

What Building Regulations Parts apply to a 30m² outbuilding?

A 30m² outbuilding requires a Building Regulations application that addresses the following Parts of the Building Regulations 2010:

  • Part A — Structure. The foundations must be adequate for the ground conditions. Most 30m² outbuildings use strip foundations of at least 450mm depth, with concrete of the appropriate mix. The walls must be of a construction appropriate for the load.
  • Part B — Fire safety. A 30m² outbuilding within 1 metre of the house, or within 1 metre of a boundary, must have fire-resisting walls to prevent fire spread. The exact requirement depends on the distance from the boundary and the size of the outbuilding.
  • Part C — Site preparation and resistance to contaminants and moisture. The floor and walls must be protected against ground moisture, with appropriate DPC and DPM.
  • Part F — Ventilation. The outbuilding must provide adequate background ventilation (typically trickle vents) to prevent condensation.
  • Part K — Protection from falling, impact and collision. Any glazing in the outbuilding must be safety glass in critical locations (low-level panels, doors, bathing areas).
  • Part L — Conservation of fuel and power. A 30m² outbuilding that is heated must meet the current U-value targets in Part L. The walls, floor, and roof must be insulated to current standards. If the outbuilding is unheated (e.g. a store), Part L does not apply.
  • Part N — Glazing safety. Glazing in doors and low-level panels must be safety glass.
  • Part P — Electrical safety. Any electrical work carried out as part of the outbuilding (e.g. a new lighting circuit or power sockets) must comply with Part P and be carried out by a Competent Person or notified to the local authority.

For a 30m² outbuilding with no fixed heating and no electrical work, the most commonly relevant Parts are A, B (if near a boundary), C, K, and N.

Planning permission for a 30m² outbuilding

A 30m² outbuilding triggers both Building Regulations and planning permission considerations. The two regimes are separate and both may apply.

Under the Town and Country Planning (General Permitted Development) (England) Order 2015 (the GPDO), an outbuilding is Permitted Development within the curtilage of a house if it meets a number of conditions, including:

  • The outbuilding is not in front of the principal elevation of the house.
  • The outbuilding, together with any other outbuildings, does not cover more than 50% of the curtilage of the original house.
  • The outbuilding is no higher than 2.5 metres if it is within 2 metres of a boundary, or 4 metres overall (with a dual-pitch roof) or 3 metres overall (with any other roof) anywhere in the curtilage.

A 30m² outbuilding is unlikely to exceed the 50% curtilage test on most properties, but it should be checked. The 4m height limit and the 2m-from-boundary 2.5m height limit also need to be observed for Permitted Development.

Where the outbuilding does not meet the Permitted Development conditions (e.g. on a property in a Conservation Area, in the grounds of a listed building, or where the LPA has removed PD rights via an Article 4 Direction), a full planning application is required.

For a worked example of an LPA-specific planning process, see our Bradford planning portal guide or our Allerdale planning guide (which covers the post-2023 Cumbria reorganisation).

How to apply for Building Regulations approval for a 30m² outbuilding

The application process for a 30m² outbuilding is the same as for any other Building Regulations project. The two routes are:

  1. Full Plans application. Submit detailed drawings and specifications to the Building Control body before work starts. The drawings are checked against the Building Regulations and either approved or returned with comments.
  2. Building Notice. A shorter, simpler route for smaller works. You give the Building Control body at least 48 hours’ notice of work starting.

For a 30m² outbuilding, the Full Plans application is the safer option because it gives certainty on the design before construction begins. The Building Notice route is technically available but is not recommended for projects of this size.

The application fee varies by local authority but is typically £300–£600 for a 30m² outbuilding. The fee covers the plans check and the site inspections at key stages (excavation of foundations, oversite, completion).

For the broader application process, see our Building Control Application guide and our Building Notice guide.

Using a Competent Person Scheme

Some trade associations operate Competent Person Schemes that cover outbuildings and similar structures. The relevant schemes are typically:

  • Structural — the foundation and structural frame work is generally not covered by a Competent Person Scheme and requires a full Building Control application.
  • Electrical — NICEIC, NAPIT, or ELECSA can self-certify Part P electrical work.
  • Plumbing and drainage — WaterSafe can self-certify water supply and drainage work.

If the outbuilding includes electrical or plumbing work, the relevant Competent Person Scheme member can self-certify that work and the homeowner is spared a separate application for that aspect. The structural and fire-safety aspects of the outbuilding still require a full Building Regulations application to the local authority.

The Completion Certificate for a 30m² outbuilding

On satisfactory completion of the work, the Building Control body issues a Completion Certificate. For a 30m² outbuilding, this is the same document as for any other building work and is equally important when the property is sold.

The buyer’s solicitor will ask for the Completion Certificate as part of the standard conveyancing process. Without it, the buyer’s solicitor may:

  • Insist on a discounted purchase price to cover the cost of retrospective certification (a regularisation application, typically 150% of the standard fee).
  • Insist on the outbuilding being inspected before exchange of contracts.
  • Apply for indemnity insurance as a cheaper alternative.

For more on the Completion Certificate, see our Building Regulations Compliance Certificate guide.

Next steps and resources

Editorial note. This article is for guidance only and does not constitute regulated advice. The Building Regulations requirements for a 30m² outbuilding depend on the specific design, location, and intended use. For project-specific questions, consult a Building Control inspector or a chartered surveyor registered with RICS.