Planning Permission for Extensions: What Falls Under Permitted Development and What Doesn't

Quick Answer: Most single-storey rear extensions to terraced and semi-detached houses up to 6m, and detached up to 8m, are Permitted Development under Class A of the GPDO 2015 (as amended), provided height, materials and boundary distance limits are met. Extensions on flats, over original house height, beyond 50% of original curtilage, in Conservation Areas, or to Listed Buildings always need full planning. Always apply for a Lawful Development Certificate (£103) on PD work — without it, future buyers face mortgage and conveyancing delays.

Summary

The Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO 2015) is the legislation that determines whether a domestic extension needs full planning permission or can proceed under Permitted Development (PD). Get it wrong and the consequences are severe: enforcement notice within 4 years (or potentially 10 years for non-Conservation Area work), forced demolition, and criminal liability for non-compliance with an enforcement notice. Get it right and the project saves 8–12 weeks of planning timeline and £206 in application fees.

This guide covers the four PD classes most relevant to UK house extensions (Class A rear/side extensions, Class B roof extensions, Class C roof alterations, Class E garden buildings), the conditions and limits that apply to each, and the categories of property where PD is restricted or removed entirely. It includes the Larger Home Extension prior approval process (the "neighbour consultation scheme") and the always-needed Lawful Development Certificate route that documents PD compliance.

The most common — and most dangerous — error: a builder advising "this is permitted development, no planning needed" without checking the Article 2(3) status of the property (Conservation Areas, AONB, World Heritage Sites have restricted PD), without checking Article 4 directions (locally removed PD), without checking the property's planning history (PD already used up by previous owners), or without producing a Lawful Development Certificate. PD is a statutory entitlement only if all conditions are met — failing any one condition means the work needs full planning permission, retrospectively if necessary.

Key Facts

Quick Reference Table — Class A Extension Limits

Need to quote compliant work? squote includes relevant regulations in your quotes.

Try squote free →
Property Type Single-Storey Rear Two-Storey Rear Side Extension
Detached 4m default / 8m with prior approval 3m half-width, 4m max height
Semi-detached 3m default / 6m with prior approval 3m half-width, 4m max height
Terraced (mid) 3m default / 6m with prior approval 3m half-width, 4m max height
Terraced (end) as semi-detached 3m as detached
Flat (any) NOT PD — full planning required NOT PD NOT PD
Maisonette NOT PD NOT PD NOT PD

Detailed Guidance

Single-storey rear extensions (Class A)

The headline figures most builders quote — 6m for semi/terrace, 8m for detached — are the Larger Home Extension limits, which require prior approval (a "neighbour consultation scheme") not full planning. Under the standard PD without prior approval, the limits are 3m and 4m respectively.

Conditions for any Class A single-storey rear extension:

The "rear wall of the original house" rule is the trap that catches builders working on properties with previous extensions. If the house already has a 3m extension, a "new" 3m extension does not become a 6m extension — the new extension must be measured from the original 1948 rear wall, and 3m + 3m = 6m, which exceeds the standard 3m PD limit.

Larger Home Extension prior approval

For single-storey rear extensions over 3m (semi/terrace) or 4m (detached) and up to 6m or 8m respectively:

  1. Submit a prior approval application to the local planning authority (LPA) before starting work
  2. The LPA notifies adjacent neighbours, who have 21 days to object
  3. If no objections: prior approval is granted (or deemed granted after 42 days)
  4. If objections: the LPA decides on impact to neighbouring amenity (typically light, privacy, outlook)
  5. Decision within 42 days; if no decision, deemed granted
  6. Application fee: £120 (England 2026)

This is faster than full planning but slower than zero-process PD — typically 6–8 weeks total. It still produces a planning record that conveyancing solicitors check.

Two-storey rear extensions (Class A)

Two-storey extensions under PD are tightly constrained:

Most two-storey rear extensions exceed at least one limit — in particular the 7m boundary distance rules out almost all terraced and tightly-spaced semi-detached properties. Full planning is the norm.

Side extensions (Class A)

Single-storey side extensions only — two-storey side extensions are NOT permitted development.

Conditions:

A side return extension to a terraced house typically meets all conditions. A wraparound (rear + side) extension is more complex — both must comply with their respective Class A conditions, and the combined footprint must respect the 50% curtilage limit.

Roof extensions and dormers (Class B)

Dormers and roof additions:

Loft conversions with rear dormers usually qualify. Front-facing dormers do not (visible from highway). See the loft dormer design and PD compliance for detailed routing.

Outbuildings and garden buildings (Class E)

Garden offices, sheds, summerhouses:

A garden office for working from home meets these limits. A garden room with sleeping accommodation does not — that becomes a dwellinghouse and triggers full planning. See the garden room PD and Building Regs guide.

Properties where PD is restricted or removed

Designation PD Status
Conservation Area Reduced — Class A side extensions removed; Class B not allowed; cladding restrictions
AONB / National Park Reduced — same as Conservation Area generally
World Heritage Site Reduced — same as Conservation Area
Listed Building (Grade I, II*, II) All work needs Listed Building Consent regardless of PD status
Article 4 Direction area Specified PD rights removed locally
Flats and maisonettes NO PD for extensions — full planning always
Houses in Multiple Occupation (Class C4) Reduced PD
New build with planning condition removing PD Check planning conditions on original consent

Article 4 Directions are increasingly common in urban Conservation Areas, where local authorities use them to control replacement of windows, removal of front gardens for hardstanding, and other minor alterations that have a cumulative impact on streetscape. Always check Article 4 status on the LPA website.

Lawful Development Certificate (LDC) — the documentation route

An LDC application asks the LPA to confirm that proposed work is PD. Two types:

The LDC is not a planning permission — it's a legal certificate that the work is/was PD. Its value:

Best practice: every PD extension gets an LDC. The £103 cost is trivial against the future conveyancing benefit.

Application fees (England 2026)

Application Type Fee
Householder planning (extensions) £258
Larger Home Extension prior approval £120
Lawful Development Certificate (proposed) £103
Lawful Development Certificate (existing) £206
Listed Building Consent £0 (no fee)
Removal/variation of conditions £258
Discharge of conditions £43 per request

Wales and Scotland have different fee scales.

For homeowners — the practical checklist

Before assuming PD covers your extension:

  1. Property type — flat or maisonette? = full planning needed
  2. Designations — Conservation Area? AONB? Listed? = check LPA website
  3. Article 4 — locally-removed PD? = check LPA website
  4. Planning history — previous extensions? Original house was as-built or 1948 boundary?
  5. Rear projection limits — 3m default / 6m with prior approval (semi/terrace), 4m / 8m (detached)
  6. Height limits — 4m max overall, 3m max eaves if within 2m boundary
  7. Materials — must be "similar" to existing
  8. Curtilage — total additions stay below 50% of original
  9. Boundary distance — 2m boundary triggers 3m eaves limit
  10. LDC application — always apply for one even on clear PD work

If steps 1–9 all pass, proceed with confidence and apply for an LDC. If any fail, full planning is the safer route — £258 fee + 8 weeks vs the risk of enforcement and demolition.

Frequently Asked Questions

Do I need planning permission for a single-storey rear extension under 3m?

Generally no, provided all the Class A conditions are met (height, materials, curtilage, designations, etc.). Under 3m doesn't automatically mean no planning needed — it means the rear projection limit is met, but every other Class A condition still applies. Always apply for a Lawful Development Certificate to formalise the position.

Does a conservatory count as an extension for PD purposes?

Yes. Conservatories were once treated separately under earlier Permitted Development law, but since 2008 they're treated as Class A extensions. All the same conditions apply: height, projection, curtilage, materials, designation status. A conservatory exceeding the 3m/4m PD projection limit needs full planning.

Can I build an extension that uses up the last of the 50% curtilage allowance?

Yes — but you cannot then build any further outbuilding, garden room, or extension under PD. The 50% rule is cumulative across all additions and outbuildings. Run a careful curtilage measurement before committing — the 50% calculation excludes the footprint of the original house but includes anything added since.

What happens if a builder builds beyond PD without planning permission?

The local authority can issue an enforcement notice requiring removal or modification. Time limits: 4 years from completion of building work for breaches of planning control (single residential dwelling), or 10 years for change of use breaches. Once enforcement is issued, work must comply within the time specified or it's a criminal offence. Owners can apply for retrospective planning, but if refused, demolition is the remedy. Cost: typically £15,000–£40,000 to demolish a non-compliant rear extension.

Do PD extensions need Building Regulations approval?

Yes, almost always. Permitted Development is about planning permission only. Building Regulations are separate and apply regardless of planning status. An extension over 30m² without Building Regs sign-off is non-compliant and unmortgageable. Submit a Building Notice or full plans application to the LABC alongside (or instead of, since they're independent) the LDC application.

Regulations & Standards