Permitted Development for Extensions: Limits and Conditions

Summary

Permitted Development Rights (PDR) are the most-used route to extending a UK home without planning permission, but they are also the most misunderstood. Customers (and some tradespeople) assume "permitted development means no permission needed" — true in some cases, but with detailed limits that, if exceeded by even a few centimetres, kill the PDR and trigger a full planning application.

The 2015 Order (with subsequent amendments) sets out the classes of work that are permitted as of right. Class A covers householder extensions — by far the most common application. The rules cover projection, height, eaves, footprint coverage, material match, side window obscuring, and the absolute exclusions (listed buildings, conservation areas, Article 4 directions, designated areas, new dwellings).

This article focuses on England — Scotland, Wales, and Northern Ireland each have their own GPDO equivalents with different limits. Tradespeople working across borders MUST check the local rules; the English limits do not apply, and a Welsh customer told "this is permitted" by a tradesperson quoting English limits has no recourse if the local planning authority enforces.

The cost angle: the Lawful Development Certificate (LDC) is not free (£135 in England as of 2025), but it provides legal certainty that the work is permitted. For any extension at the edge of PDR limits — and for any future sale — the LDC is worth getting before starting work.

Key Facts

• Primary legislation (England) — Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2 Part 1 (most recent amendment: 2024 Permitted Development Amendment Order)
• Wales — Town and Country Planning (General Permitted Development) Order 1995 (as amended for Wales)
• Scotland — Town and Country Planning (General Permitted Development) (Scotland) Order 1992 (as amended)
• Northern Ireland — Planning (General Permitted Development) Order (Northern Ireland) 2015
• Class A (England) — Single Storey Rear Extension — Up to 4m projection for detached / 3m for semi/terrace; up to 8m / 6m under Prior Approval (Larger Home Extension scheme)
• Class A max ridge height — 4m above original ground level
• Class A eaves height — Within 2m of boundary: max 3m eaves
• Materials rule — Must be similar in appearance to the existing dwelling
• 50% rule (Class A) — Total ground covered by extensions (existing + proposed) must not exceed 50% of the curtilage (excluding the original house)
• Side extension limits — Half-width of original house; single-storey only; eaves max 3m
• Two-storey extension — Class A; max 3m projection; not within 7m of rear boundary; pitched roof required
• Listed buildings — PDR usually withdrawn; full planning + listed building consent required
• Conservation areas — Side extensions and cladding alterations need planning; rear extensions still possible under PDR
• Article 4 directions — Local authority withdrawal of specific PDRs; check with LPA before assuming PDR applies
• Prior Approval (Larger Home Extension) — Notification + 42-day consultation period; neighbours may object; LPA decides on impact
• Lawful Development Certificate (LDC) — Optional formal confirmation that work is permitted; £135 fee in England (2025); recommended for any work at the edge of limits and for resale evidence
• Original dwelling — Means the dwelling as it existed on 1 July 1948 or as originally built if later; previous extensions count against the 50% rule

Quick Reference Table

Detailed Guidance

The Rules in Practice — Single-Storey Rear Extension

The most common PDR job. For a typical 1930s semi:

• Maximum projection: 3m beyond original rear wall (6m under Prior Approval Larger Home Extension)
• Maximum height: 4m above original ground level (the ground level immediately adjacent to where the extension will sit)
• Eaves height: 3m maximum if any part of the extension is within 2m of the boundary (typical for rear extensions on narrow plots)
• 50% rule: All extensions and outbuildings combined must not cover more than 50% of the original curtilage (i.e. land around the house excluding the house footprint)
• Materials: Brick, render, tile etc. must be similar to the existing — exact match not required but "obviously different" (e.g. weatherboarding on a brick house, or a flat parapet roof on a pitched-roof house) may fall outside PDR

Prior Approval — Larger Home Extension Scheme

Where a single-storey rear extension exceeds the standard 3/4m limit but stays within 6/8m, Prior Approval is required:

1. Apply to LPA with plans showing the proposal
2. LPA notifies neighbours; 21-day objection period
3. LPA assesses impact (loss of light, overlooking, character) on objections only
4. Decision within 42 days; silent = deemed approved

This is faster and cheaper than full planning, but the LPA can refuse if objections are valid. Typical refusal rates are 5–15% depending on the area.

Two-Storey Rear Extension

Class A limits:

• 3m maximum projection from rear wall (no Prior Approval larger version)
• Not within 7m of any boundary opposite the rear wall (i.e. the back-fence boundary)
• Pitched roof required (flat roof typically needs planning)
• Eaves height matching existing; ridge height not above existing ridge

Two-storey extensions trigger more frequent planning refusals than single-storey; if the design pushes any limit (eaves, materials, roofscape) get pre-application advice from the LPA before committing.

Side Extensions

Side extension PDR is restrictive:

• Single-storey only
• Maximum half the width of the original house
• Eaves height max 3m
• NOT permitted in a designated area (conservation area, AONB, etc.)
• Materials must match existing

Many "obvious" side extensions exceed these limits and need full planning. Don't assume because a neighbour built one, yours will be PDR.

Class B — Loft Conversions

A separate PDR class covering loft alterations (dormers, hip-to-gable, rear roof extensions). The key limit is volume:

• 40m³ for terraced houses
• 50m³ for semi-detached and detached
• Volume measured externally (any roof extension, mansard, dormer counts)
• Front-facing dormers/extensions visible from a public highway always need full planning
• Materials must match existing

Class E — Outbuildings

Garden rooms, garages, garden offices etc.:

• Single-storey only
• Maximum eaves 2.5m if within 2m of boundary; otherwise 3m
• Maximum ridge 4m (dual-pitch roof) or 3m (any other roof)
• Total ground coverage of all outbuildings + extensions must not exceed 50% of the curtilage
• Cannot be used as a separate dwelling (no kitchen + bathroom + sleeping arrangement intended as primary residence)

Listed Buildings and Conservation Areas

Listed buildings: All PDR is withdrawn. Any work — even routine repointing, replacing windows, removing an internal partition — may require Listed Building Consent. Get pre-application advice from the LPA's conservation officer before starting.

Conservation areas: Some PDR remains (rear extensions can be PDR), but:

• Cladding (rendering, tile hanging, weatherboarding) any face requires planning
• Side extensions are NOT PDR
• Roof alterations are restricted

Always check the conservation area's "appraisal" document, which sets out what the LPA considers important to character.

Article 4 Directions

A LPA can issue an Article 4 direction removing specific PDR in a defined area — typically used in conservation areas, sensitive estates, or where uncontrolled PDR development would harm character. Check with the LPA's online planning service before quoting any PDR work. The direction's effect: work that would otherwise be PDR now needs full planning.

Building Regulations Are Separate

PDR is about planning permission. Building Regulations (Approved Documents A, B, C, etc.) are separate and apply to almost all extensions regardless of PDR status. An extension can be:

• PDR (no planning needed) AND fully compliant with Building Regs (Building Control sign-off needed)
• PDR (no planning needed) AND NOT Building Regs compliant — you'll have problems at sale
• Planning approved AND not Building Regs compliant — same problem
• Full planning needed (over PDR limits) AND Building Regs compliant — both processes needed

Customers often conflate the two. Always explain: "Planning is about whether you can build it; Building Regs is about how you build it. We need both."

The Lawful Development Certificate

The LDC is an optional but recommended route to legal certainty. The LPA reviews your proposal and issues a certificate confirming the work is permitted. Benefits:

• Legal protection: any future challenge fails because the LDC stands
• Resale: buyers' solicitors look for LDCs on extensions; without one, indemnity insurance often required
• Mortgage: some lenders require LDCs on extensions to lend

Cost £135 (England 2025). Process ~8 weeks. Recommended for any extension at the edge of PDR limits or in any area where the LPA's stance is unclear.

Worked Example: 3m × 4m Rear Extension on a Semi-Detached

Scenario: 1950s semi, 100m² original ground floor area. Proposed 3m projection × 4m wide single-storey rear extension. Eaves height 3m, ridge 3.8m. Brick to match existing, slate roof to match existing.

PDR check:

• Projection: 3m ≤ 3m allowed for semi ✓
• Ridge height: 3.8m ≤ 4m ✓
• Eaves: 3m (within 2m of boundary — assume yes) ≤ 3m ✓
• Materials: similar ✓
• 50% rule: existing 100m², proposed extension 12m². Total extension <50% of (curtilage area - house footprint) ✓
• Not in a conservation area, not listed, no Article 4 ✓

Conclusion: PDR applies. Lawful Development Certificate recommended (£135).

If the projection were 3.05m instead of 3m, PDR is lost and full planning is required (£258 fee + 8 weeks + risk of refusal). The 50mm matters.

Frequently Asked Questions

Can I rely on a builder's word that my extension is permitted development?

Get a Lawful Development Certificate from the LPA before starting work. A builder's opinion isn't legal cover — only an LDC is. The £135 fee is a small fraction of the cost of getting the wrong answer.

What if I'm in a conservation area?

Rear extensions are usually still PDR but cladding alterations need planning, side extensions are not PDR, and the LPA may have an Article 4 direction further restricting PDR. Check the LPA's online planning portal and conservation area appraisal before committing to anything.

Does the 50% rule include sheds and garages?

Yes. The 50% rule covers ALL extensions and outbuildings (existing + proposed) against the original curtilage minus the original house footprint. Pre-existing sheds, garages, conservatories all count. Demolishing an old shed before building can free up the percentage allowance.

Can I extend a flat under PDR?

Flats have very limited PDR — most material alterations to flats need planning permission. The Permitted Development Order treats flats differently from houses. Always assume planning permission is needed for flat alterations until you've confirmed otherwise.

What's the difference between Prior Approval and full planning?

Prior Approval: notify + 42-day consultation; LPA assesses specific impacts (typically light, overlooking, character) and approves if no significant harm. Faster, cheaper, narrower review.

Full planning: full application; LPA assesses against the entire local plan, design guidance, neighbour comments. Slower (typically 8 weeks), more expensive, broader review.

Prior Approval is available for specific PDR-extension scenarios (Larger Home, change of use, telecoms etc.); full planning is for everything else not covered by PDR.

Regulations & Standards

• Town and Country Planning (General Permitted Development) (England) Order 2015 — The primary PDR legislation for England; updated periodically

• Town and Country Planning Act 1990 — Foundation planning law

• Town and Country Planning (Listed Buildings and Conservation Areas) Act 1990 — Listed building and conservation area rules

• National Planning Policy Framework (NPPF) — Government planning policy; LPAs apply this in decisions

• Permitted Development Order (Wales) / (Scotland) / (NI) — Separate equivalents for devolved nations

• Planning Practice Guidance — Online government guidance interpreting planning rules

• Planning Portal (England) — Householder permitted development reference; application route

• GPDO 2015 on legislation.gov.uk — Statutory text

• Planning Practice Guidance — Government interpretation

• RIBA Plan of Work — Industry process reference

• building over a sewer build over agreement — Related consent process

• building control — Building Regs sign-off (separate process)

• party wall notices — Party Wall etc. Act process

• building regulations overview — Building Regs overview