Planning a home extension is one of the most rewarding investments you can make in a UK property — but the planning rules around what you can build without permission are widely misunderstood. Get it wrong and you face enforcement action, a requirement to demolish, and serious complications when you come to sell. Get it right and you can add 10–15% to the value of a typical semi-detached home without a single planning application.
This guide sets out the current rules for England under the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO), updated to reflect current thresholds — so you can make the right call before investing a penny.
Permitted Development: What It Means
Permitted development (PD) is planning permission granted by Parliament rather than by your local council. If your proposed extension falls within the PD rules (Class A for dwellinghouses), you do not need to submit a Householder Application. The council has no general discretion to refuse it — though they can check compliance.
PD rights apply to houses only. Flats, maisonettes, and converted properties do not have PD rights under Class A. Listed buildings require listed building consent for any extension. Conservation areas impose additional restrictions. For a complete picture of all PD classes — including Class B loft conversions, Class E outbuildings, and commercial-to-residential changes of use — see the complete guide to permitted development rights in the UK.
Single-Storey Rear Extension: PD Limits
Under Class A, a single-storey rear extension is permitted development if:
- It does not extend beyond the rear wall of the original dwelling by more than 3 metres (attached house) or 4 metres (detached house)
- Maximum height: 4 metres
- The roof pitch matches the main house where the eaves height exceeds 3 metres
- It does not exceed half the width of the original house if it extends beyond the side elevation
The Prior Approval / Neighbour Consultation Scheme (introduced 2013, made permanent 2019) allows larger single-storey rear extensions under Class A:
- Up to 6 metres beyond the rear wall (attached) or 8 metres (detached)
- Subject to: Prior Approval application to the council, 42-day neighbour consultation, and the council's assessment being limited to the impact on adjoining owners' amenity only (not general planning merits)
If no objections are received or the council raises no issues within 42 days, the extension can proceed. If objections are received, the council may refuse — but only on amenity grounds.
Two-Storey Rear Extension: PD Limits
A two-storey rear extension is PD if:
- It does not extend beyond the rear wall of the original dwelling by more than 3 metres
- The extension is no closer than 7 metres to the rear boundary
- The 45-degree rule (cone of vision from the nearest opposite window) is respected — though this is a design guide rather than a statutory PD condition
Two-storey rear extensions do not benefit from the extended limits under the neighbour consultation scheme — the 3m limit is absolute for two-storey.
Side Extension: PD Limits
A single-storey side extension is PD if:
- Its width is no more than half the width of the original house
- Its height does not exceed 4 metres
- It is set back from the principal (front) elevation
No two-storey side extensions are permitted development — these always require a Householder Application.
Class A Conditions: What All Extensions Must Meet
Regardless of size, all Class A extensions must comply with the following conditions:
| Condition | Detail |
|---|---|
| No more than 50% of curtilage covered | Original curtilage only; all additions cumulative |
| Materials match original house | Reasonably similar in appearance |
| No balconies or raised platforms | Including Juliet balconies with external access |
| No verandas | Unless within an existing structure |
| Does not extend forward of the principal elevation | No front extensions as PD |
| Height ≤ 4m (single-storey) | Or ridge of main roof if lower |
The 50% curtilage rule is cumulative — it includes all outbuildings, garages, and previous extensions, not just the new extension. Many properties with an existing garage and conservatory are already close to or over the limit. If you are also considering a garden room or outbuilding alongside the extension, the Class E permitted development guide for outbuildings and garden rooms explains how both footprints count toward the same 50% limit.
What Triggers Full Planning Permission
You must submit a full Householder Application if:
- The extension exceeds the PD size limits
- The property is in an Article 4 Direction area that removes PD rights
- The property is a listed building (requires listed building consent regardless)
- The property is a flat or maisonette (no Class A PD rights)
- The property is in a designated area (conservation area, AONB, National Park) and the extension is on a side or rear wall not visible from the road — check local authority guidance
- The extension includes a balcony or raised platform
In conservation areas, Class A still permits rear extensions but side extensions are removed from PD rights.
Prior Approval vs Householder Application: Comparison Table
| Factor | Prior Approval (Neighbour Consultation) | Householder Application (Full Planning) |
|---|---|---|
| Fee | £206 | £258 |
| Timescale | 42 days (6–8 weeks) | 8–13 weeks |
| Grounds for refusal | Amenity/privacy impact on adjoining owners only | Any material planning consideration |
| Neighbour objections | Relevant to amenity assessment only | Considered in full |
| Publicity requirement | Limited | Full (site notice, neighbour letters) |
| Right of appeal | Yes (written representations) | Yes (written reps / hearing / inquiry) |
| Applicable extensions | Single-storey rear only, within size limits | Any extension not covered by PD |
Lawful Development Certificate: The £103 Insurance Policy
A Lawful Development Certificate (LDC) from the council confirms that your completed or proposed development is lawful. It costs £103 for a proposed development in England (same fee as for PD outbuildings).
An LDC is not mandatory — but it is strongly recommended if:
- You want certainty for mortgage lenders or future buyers
- The PD compliance is genuinely borderline
- You are in an area with complex PD history
Solicitors and mortgage lenders frequently require an LDC for extensions completed under PD, particularly in resale transactions. A £103 certificate is far cheaper than a dispute at sale. For the full step-by-step application process — including CLEUD vs CLOPUD, the evidence table, common refusal reasons, and why indemnity insurance is not a substitute — see our guide to how to apply for a Lawful Development Certificate in the UK.
Decision Flowchart (Text Form)
Is the property a house (not a flat, maisonette, or listed building)? → No: You need full planning permission or listed building consent. Stop. → Yes: Continue.
Is the extension at the rear (not side or front)? → Side, single-storey: Check it is ≤ half original house width and ≤ 4m high → PD if yes. → Side, two-storey: Full planning permission required. Stop. → Front: Full planning permission required. Stop. → Rear: Continue.
Is the extension single-storey? → No (two-storey): Is it within 3m of rear wall and 7m from rear boundary? → PD if yes (no Prior Approval available). → Yes (single-storey): Continue.
Is the extension within 3m (attached) / 4m (detached) of the rear wall? → Yes: PD without Prior Approval — check Class A conditions. → No: Is it within 6m (attached) / 8m (detached)? → Yes: Prior Approval (neighbour consultation scheme). → No: Full planning permission required.
Does the property have an Article 4 Direction removing Class A PD rights? → Yes: Full planning permission required regardless of size. → No: PD rights apply (subject to Class A conditions above).
Design Tips to Maximise PD Rights
- Stay within 3m/4m if you can — avoids the Prior Approval process entirely and the risk of an amenity objection.
- Match materials precisely — use the same brick, tile, and render specification as the original house. A council enforcer will measure "reasonably similar" strictly.
- Avoid flat roofs where possible — a pitched or mono-pitch roof keeps you within the 4m height limit and looks better at resale.
- Measure the original house, not the current footprint — PD limits are calculated from the original dwelling as built or as it stood on 1 July 1948, not from any subsequent extensions.
- Document everything — take dated photographs showing the original footprint before work begins.
Build With Confidence
Once your planning position is confirmed — whether under PD, Prior Approval, or a full Householder Application — the next step is appointing a contractor. The guide to finding and vetting a builder in the UK covers FMB and TrustMark accreditation, what a proper written quote must include, deposit norms, and what to do if things go wrong.
Note that planning permission and building regulations are two entirely separate systems. Even extensions that are permitted development still require building regulations approval — covering structural calculations, insulation, drainage, and the completion certificate that solicitors will request when you come to sell. If you are applying for full planning permission on a larger scheme, be aware that the LPA may also seek planning obligations alongside the permission — our guide to Section 106 agreements explains what those obligations typically cover and how they affect buyers on development sites. If you are considering building a completely new dwelling on your land rather than extending an existing one, the planning permission for a new build guide covers the outline vs full PP decision, local plan reading, self-build CIL exemption, and ecological survey requirements. If you are thinking about converting an existing garage rather than building an extension, the same PD vs planning question applies — see our converting a garage UK guide for the specific rules, building regulations Parts, and U-value targets that apply to garage conversions.
Whether you're exploring what's possible under permitted development or navigating a full planning application, a clear plan makes all the difference. Renovate Me gives you a step-by-step renovation roadmap tailored to your property, goals, and budget — so you build the right extension, in the right way, the first time. Start at renovate-me.madethis.app.
For a concise reference guide to all PD limits — rear extensions, two-storey extensions, outbuildings, porches, loft conversions, and garage conversions — see our Permitted Development Rights UK extensions guide.
- Garage Conversion: Permitted Development Rules and Costs UK — the integral vs detached planning distinction, Building Regs requirements, and parking condition implications for garage conversions