Permitted Development Rights Explained: What You Can Build Without Planning Permission
Author: David Campbell BA BArch MA PgDIP RIBA
Estimated reading time: 4 minutes
Ask most homeowners what permitted development means and they will say "you don't need planning permission." That is only half true, and the half they leave out is where projects go wrong.
What "permitted development" actually is
Permitted development rights are granted directly by national legislation, the Town and Country Planning (General Permitted Development) (England) Order 2015, rather than by a decision an officer makes on your specific proposal [1]. If a proposal fits entirely within a class, it can proceed without a planning application. If it exceeds any single limit, even by a small margin, the entire proposal falls outside permitted development and needs full planning permission instead, there is no partial credit. A rear extension that is 4.1 metres deep instead of 4 metres is not "almost compliant", it is a proposal requiring planning permission, full stop.
Class A: the single-storey rear extension, and its limits
Class A covers the enlargement of a house. Development is not permitted if the extension would cover more than 50% of the curtilage, exceed the height of the existing roof, or extend beyond a wall fronting a highway [1]. The standard limit for a single-storey rear extension is 4 metres for a detached house or 3 metres for any other house, up to 4 metres high. A "larger home extension" route allows this to increase to 8 metres detached / 6 metres otherwise, provided the house isn't on Article 2(3) land (broadly conservation areas and similarly designated sites) and a prior approval process is followed: adjoining owners get 21 days to object, and a single objection triggers the council's judgement on amenity before the 42-day clock resolves in your favour [1]. Two-storey rear extensions are limited to 3 metres and can't come within 7 metres of the opposite boundary; side extensions can't exceed half the original house's width.
Class B: loft conversions, and where they cannot happen at all
Roof enlargements can't add more than 40 cubic metres (terrace) or 50 cubic metres (any other house) to the roof space, counting everything added since 1948, and can't exceed the existing roof height or extend beyond the roof slope on a highway-facing elevation [2]. Critically, Class B does not apply at all on Article 2(3) land, which is why most loft conversions in London conservation areas need full planning regardless of how modest they are, a point covered in more detail in our guide to extending in a conservation area.
Why permitted development is often the wrong tool, even when available
The conditions that make Class A and B fast also make them design-limiting: matching materials, aligned roof pitches, obscure-glazing rules dictating window position rather than how a room wants to be lit. A full application costs more but buys design freedom permitted development structurally cannot offer. Deciding which route actually serves the brief, not just which route avoids an application, is design judgement.
One right, different weight by typology
Outbuildings rely on a separate class with its own limits; hospitality and commercial change of use relies on an entirely different part of the Order (Part 3), a large enough subject that we cover the current commercial-to-residential right, Class MA, separately.
The Certificate of Lawful Development: proving it, not assuming it
A Lawful Development Certificate, applied for under the Town and Country Planning Act 1990, formally establishes that a development is lawful without planning permission, producing a document a solicitor or lender can rely on. We recommend one on any scheme of real value, because an incorrect self-assessment discovered at the point of sale is far costlier than certifying properly at the outset.
Where permitted development rights disappear
Conservation area status removes Class B entirely and tightens Class A. An Article 4 Direction can go further, street by street. "My neighbour built this without permission" is not evidence you can too.
Design response: using the rules as a discipline, not a shortcut
The practices that get the most from permitted development treat the fixed envelope as a genuine design constraint, not an excuse to skip design thinking. Whether a project should use permitted development, the larger extension route, or full planning is itself a decision made at Stage 0, before any drawings are produced.
Considering an extension, loft conversion, or outbuilding and unsure which route applies? Contact Vision + Design for a clear assessment of what your permitted development rights actually allow, and whether they're the right tool for your project.
→ Email us at info@visionanddesign.co.uk
→ Or call us on 07931910243
1. Legislation.gov.uk, "The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1 — Class A" — legislation.gov.uk
2. Legislation.gov.uk, "...Class B — Additions etc to the roof of a dwellinghouse" — legislation.gov.uk