Permitted Development Rights for Extensions: What You Can Build Without Planning Permission

Quick Answer: Under Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended), a single-storey rear extension can be built without planning permission if it extends no more than 4m from the rear wall of a detached house (3m for semi-detached and terraced), is no higher than 4m, and is no wider than the original house. Larger extensions (up to 8m for detached, 6m for other) are possible under the Prior Approval Neighbour Consultation Scheme. Article 4 Directions and Conservation Areas may restrict these rights.

Summary

Permitted development (PD) rights allow certain types of construction work without needing full planning permission. They are granted by Parliament through a statutory instrument — the General Permitted Development Order (GPDO) — rather than by the local planning authority. Understanding PD rights is essential for builders, extension contractors, and any tradesperson involved in residential extensions.

The rules appear simple but are filled with conditions and exceptions. Whether a proposed extension falls within PD depends on the specific measurements, the property type, the location, the cumulative build-up since 1948, and whether the council has removed PD rights via an Article 4 Direction. Getting it wrong means an enforcement notice, potential demolition requirement, and a client who holds the contractor responsible.

This article focuses on the most commonly relevant PD classes for residential extensions in England. Scotland, Wales, and Northern Ireland have separate legislation with different limits.

Key Facts

Quick Reference Table — Class A: Single-Storey Rear Extension Limits (England)

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Property Type Standard PD (no prior approval) Prior Approval Route Height Limit Width Limit
Detached house 4m from original rear wall Up to 8m Max 4m at eaves No wider than original house
Semi-detached or terraced 3m from original rear wall Up to 6m Max 4m at eaves No wider than original house
All — — Max 4m ridge height Roof pitch of extension need not match house

Additional Class A conditions:

Detailed Guidance

How Class A Measurements Work

4m/3m measurement — taken from the rear wall of the original house (not including any previous extension). If the house already had a 2m extension added in the 1990s, the 4m allowance still runs from the original rear wall — so only 2m of new extension is possible before exceeding the PD limit.

Maximum height — 4m at the highest point; for a pitched roof extension, the ridge. For a flat roof extension, the parapet height (flat roof height limited to 3m where within 2m of a boundary).

Width — the extension must not be wider than the width of the original house. A side return infill extension is a common grey area; if the side return is being filled in and the result is wider than the original house, it may not be PD.

Eaves height at boundary — if any part of the extension is within 2m of the site boundary, the maximum eaves height is 3m. 'Eaves' means the point where the roof meets the external wall — not the ridge.

The Neighbour Consultation Scheme (Prior Approval)

For single-storey rear extensions up to 8m (detached) or 6m (other), a Prior Approval application can be made to the council. This is a lighter-touch process than full planning permission:

  1. Submit the application — form and site plan to the local planning authority
  2. Neighbour consultation period — 21 days; the council notifies adjacent neighbours; any objections are considered
  3. LPA determination — if objections raise genuine impact concerns (loss of light to neighbours, overlooking), the LPA can refuse Prior Approval; if no significant impact, Prior Approval is granted
  4. Work proceeds — must start within 3 years of Prior Approval

Key difference from PD: a neighbour cannot prevent a standard PD extension but CAN influence a Prior Approval determination if they raise material impact concerns.

Class E: Outbuildings and Garages

Outbuildings within the curtilage (a summer house, garage, home office, or garden room) are permitted development under Class E subject to:

Home offices in outbuildings are a growing sector. If the outbuilding is used only as incidental residential use (office, gym, hobby room), no change of use planning permission is needed. If it will be used for commercial purposes (business premises), planning permission for change of use is required.

Class B: Roof Additions (Dormers)

Under Class B, a dormer can be added to a roof slope not facing a public road, subject to:

Conservation areas — Class B is restricted in Conservation Areas; dormer windows on the principal elevation side are not permitted development and require full planning permission.

How to Confirm PD Status

Do not rely solely on a general guide to confirm PD. For every specific project:

  1. Check the planning record — search the local authority planning portal for the property address; check for any previous applications, conditions, or Article 4 Directions
  2. Check for Article 4 Directions — the council's PD restrictions map shows Article 4 areas; the planning department helpline can confirm
  3. Check Conservation Area designation — council interactive maps
  4. Get a lawful development certificate (LDC) — a formal application to the council for confirmation that the proposed works are PD; not mandatory but provides legal certainty and is worth approximately £206 in fees (England); strongly recommended before a project starts on site

Lawful Development Certificates

A lawful development certificate (LDC) is the mechanism to formally confirm that works are permitted development or that an existing use is lawful. For extensions:

Frequently Asked Questions

Do I need Building Regulations approval even if I don't need planning permission?

Yes — these are separate systems. Planning permission (or PD) relates to land use and impact on neighbours. Building Regulations relate to the structural integrity, fire safety, energy efficiency, and habitability of the building. Any extension, regardless of planning status, requires Building Regulations approval unless it is a very minor exempt structure (a small porch, for example, under Exempt Classes in Schedule 2 of the Building Regulations).

The council says my extension requires planning permission but I thought it was permitted development?

Article 4 Directions, planning conditions on the original house (sometimes imposed when the property was first built or when a previous extension was approved), or a specific local development plan policy can all restrict PD rights that would otherwise apply nationally. The council's decision is binding; you need to apply for full planning permission or redesign to comply with whatever restriction applies.

Can I convert a PD outbuilding into a habitable annexe?

PD rights for outbuildings (Class E) cover incidental residential use. Converting an outbuilding into a self-contained living unit (annexe) represents a material change of use and requires planning permission. Many councils are also restrictive about annexes as they can become independent dwellings; check the local authority's supplementary planning documents on annexes before advising the client.

Regulations & Standards