Planning · Updated April 2026

Do I Need Planning Permission for an Extension in 2026?

The short answer: most UK home extensions don't need planning permission in 2026. Around 75–80% fall under Permitted Development rights, meaning your build only needs Building Regulations sign-off. This guide walks through the full 2026 PD rules for rear, side, double-storey and wraparound extensions, the exceptions that trip homeowners up, and the exact process for confirming your project is PD-compliant before you spend a penny.

2026 Permitted Development rules All extension types covered Real UK process
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By the BestBuilders Editorial Team
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Quick Answer

Do I need planning permission for my extension?

Probably not. Most UK extensions fall under Permitted Development — no planning application required. Key 2026 PD rules:

  • Rear extension (single-storey): up to 6m deep on a semi/terrace, 8m deep on a detached (Larger Home Extension route). Max height 4m.
  • Double-storey rear: up to 3m deep, must be 7m+ from rear boundary, eaves ≤ existing house.
  • Side extension: max width 50% of the original house width. Single-storey only under PD.
  • Wraparound: usually needs full planning — combines side + rear past PD limits.
  • Materials must be similar to the existing house.
  • Can't exceed 50% of garden area.

Exceptions where PD doesn't apply: listed buildings, conservation areas with Article 4 Directions, AONBs, National Parks, and flats/maisonettes. In those cases, you always need planning permission.

Expert Note

The PD-volumes rule that trips up most extension planners

Permitted Development rights for extensions look simple on paper but contain a compounding rule that catches homeowners out consistently: prior extensions on the property count against your current PD allowance, even if you didn't build them. If the house had a previous owner extend 20 years ago under Permitted Development, that original extension's volume is deducted from your remaining PD allowance today.

The 50% rule makes this more restrictive than most homeowners realise. Under Article 1(5) of the GPDO, the total area of all extensions to the house (combined, not just yours) cannot exceed 50% of the curtilage of the house as it stood on 1 July 1948 (or when it was first built, if later). "Curtilage" means the area of the plot excluding the original footprint of the house itself. On a 200m² plot with a 75m² original house, the curtilage is 125m² — and the combined extension area can't exceed 62.5m². If previous owners added a 35m² conservatory and a 15m² porch, you have only 12.5m² of PD extension volume remaining. Go beyond that, and you need full planning regardless of how small your new extension is.

Before commissioning an architect, do two free checks: (1) pull up every planning application on your property through your local council's planning portal search (takes 10 minutes, free); (2) overlay the original house footprint with any outbuildings, porches, conservatories and extensions visible today using the OS Maps historical-layer tool (free on the gov.uk site). Add up all existing additional volumes, subtract from the 50% curtilage allowance, and you have your remaining PD headroom. If you're over, apply for a Certificate of Lawful Development (£129) before designing — it's the cheapest way to avoid an expensive design being refused at the submission stage.

Written by the BestBuilders Editorial Team. Based on platform quote data, industry research and primary UK source material. Reviewed 20 April 2026. Questions: info@bestbuilders.co.uk.

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Permitted Development Rules

2026 Extension PD Rules by Type

The Town and Country Planning (General Permitted Development) Order sets the rules. Here's the 2026 summary for each extension type:

Type Max Depth Max Height Notes
Single-storey rear (terrace / semi) 3m (standard) / 6m (Larger Home) 4m Larger route needs Neighbour Consultation Scheme approval
Single-storey rear (detached) 4m (standard) / 8m (Larger Home) 4m Larger route needs Neighbour Consultation Scheme approval
Double-storey rear 3m Must match existing eaves height Must be 7m+ from rear boundary; no balcony/terrace
Side extension (single-storey) No specific depth limit 4m, eaves 3m if within 2m of boundary Width ≤ 50% of original house width
Side extension (two-storey) N/A N/A NOT permitted under PD — always needs planning
Wraparound N/A N/A Almost always needs planning (combines side+rear past PD limits)
Flat roof over 3m depth As per type 3m to eaves, 4m to roof Rooflights adding ≤15cm above the roof plane only

The 50% rule: across all extensions combined, you cannot build on more than 50% of the land surrounding the original house (as it stood on 1 July 1948, or when first built if later). Previous extensions count toward this limit even if not done by you.

When PD Doesn't Apply

6 Situations Where You Always Need Full Planning

1

Listed buildings

Any external work to a Grade I, II* or II listed building requires Listed Building Consent — full stop. You also need planning permission for the extension itself. Fines up to £20,000 or prosecution for unconsented work.

2

Conservation areas (Article 4)

Many conservation areas have Article 4 Directions that remove PD rights. Your council's website lists these. Always check before assuming PD applies.

3

Flats & maisonettes

PD rights under Class A only apply to dwellinghouses — not flats or maisonettes. Any extension, balcony or roof-level change needs full planning regardless of size.

4

AONBs, National Parks & Broads

In these "designated areas," PD volumes are more restrictive and side extensions are excluded entirely. Always verify with the local planning authority before assuming PD.

5

Wraparound extensions

Combining a rear and side extension into a single L-shape almost always exceeds PD limits and needs full planning. A common homeowner mistake is to treat each half as a separate PD extension.

6

Front or facing-highway extensions

Any extension on the principal elevation (usually the front), or any side elevation that fronts a highway, is excluded from PD. Porches have their own separate PD rules with tight limits.

The Process

4 Steps to Confirm PD Before Spending on Your Extension

  1. Check property status online. Enter your postcode on the MAGIC map (defra.gov.uk) and your council's Planning Portal. Flags for: listed building status, conservation area, Article 4 Direction, AONB, SSSI, Green Belt. 10 minutes of free research saves £1,000s.
  2. Check any prior extensions at the property. Previous owners' extensions count toward your PD allowance. Your council's planning records (free online) list every approved extension. Add up the volumes — if you're already near the 50% curtilage rule, full planning may be needed.
  3. Apply for a Lawful Development Certificate (LDC). Optional, but highly recommended. £129 fee, 6–8 week decision. The LDC is a legally binding council statement that your extension is PD-compliant. Your buyer's solicitor will thank you at resale — without one, buyers often demand 2–5% off for the planning risk.
  4. Apply under the Neighbour Consultation Scheme (if Larger Home route). For 6m (semi/terrace) or 8m (detached) rear extensions, you need to notify your neighbours via your council. They have 21 days to object; if there's no objection, approval is typically granted. £204 application fee, 6 week process.
~78%
Of UK extensions fall under PD
£129
Lawful Development Certificate fee
8 wks
Typical full planning decision time
83%
Of UK extension applications approved
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FAQs

Extension Planning Permission Questions (UK 2026)

Usually no. Single-storey rear extensions up to 6m deep on a semi/terrace or 8m deep on a detached fall under Permitted Development (Larger Home Extension route), needing only a neighbour consultation not full planning. Double-storey rear extensions up to 3m deep are also PD, provided they're at least 7m from the rear boundary. You'll always need planning if your property is listed, in a conservation area with Article 4, or if prior extensions have already used up the PD allowance.
On a detached house under the Larger Home Extension PD route: an 8m deep × full-width rear extension, up to 4m high. That's typically 25–40m² of floor area without needing planning. On a semi or terrace: 6m deep × full-width. Combined with a side return (single-storey only, ≤50% house width), you can often create 40–60m² of new space entirely under PD, as long as you stay below 50% of total curtilage coverage.
For a single-storey side extension of less than half the original house's width, usually no — it falls under PD. For a two-storey side extension, yes — always. Two-storey side extensions are explicitly excluded from PD rights. Side extensions on corner plots or that face a highway also typically need planning because they're on an "elevation facing a highway."
A Lawful Development Certificate (LDC) is a formal council confirmation that your extension is Permitted Development and doesn't need planning. You don't legally need one to proceed — but it's strongly recommended. At £129 with a 6–8 week turnaround, it's cheap insurance: it protects against future enforcement action and prevents buyers (or their solicitors) from challenging the extension at resale. An LDC also makes conveyancing substantially smoother at sale time.
If planning was required but not obtained, the council can serve an Enforcement Notice requiring demolition or modification of the extension. You can apply for retrospective planning permission, but it's risky — refusal rates are higher and you've already spent the money. After 4 years the council loses the right to enforce on unauthorised building work (10 years for listed buildings), but during that window you cannot sell the property cleanly. For listed buildings, unauthorised works are a criminal offence with fines up to £20,000.
A full householder planning application takes 8 weeks from validation in most UK councils — though some are running at 12 weeks in 2026 due to backlogs. Straightforward applications in suburban areas are usually approved (~83% national approval rate). Applications in conservation areas, on listed buildings, or opposed by neighbours can take 12–16 weeks and may go to committee. A Neighbour Consultation Scheme application (for PD Larger Home Extensions) takes 6 weeks.
If retrospective planning is refused, the council can issue an Enforcement Notice requiring you to demolish or modify the unauthorised work within a specified timescale (typically 3–12 months). You have the right to appeal to the Planning Inspectorate within 28 days of the notice — appeals are decided in your favour about 30% of the time nationally. If the appeal fails and you don't comply with the notice, the council can prosecute (fines up to £20,000 at magistrates' court, unlimited at Crown Court) and can ultimately enter the property to complete the demolition at your cost. After 4 years of continuous breach without enforcement action, most operational development becomes immune — but the 4-year clock doesn't start while the council is actively investigating.
Neighbour objection alone cannot block a Permitted Development extension — PD rights bypass the consultation process entirely (except for the Larger Home Extension scheme, where the Neighbour Consultation process does give neighbours formal objection rights). For full planning applications, neighbour objections must be based on material planning considerations: loss of light, privacy, visual impact, parking, highway safety. Objections based on property value, personal disputes or construction-period disruption are not valid planning considerations and should be disregarded by the case officer. However, strong objections on material grounds can trigger a planning committee hearing rather than officer delegation, which significantly increases refusal risk. Pre-application consultation with neighbours before formal submission usually de-escalates objections and is worth the 2–3 weeks it adds.
Three years from the date of the decision notice, as standard. You must commence development within this period — "commence" usually meaning a material start on site (dug foundations, demolition of existing structures). After commencement, there's no legal deadline to complete. If you don't commence within 3 years, the permission lapses and you'd need to re-apply — with no guarantee of the same decision, especially if local policy has changed. Some permissions grant a longer or shorter validity (1–5 years) where the council specifies — always read the decision notice and diary the commencement deadline. A simple "break ground" operation (even just digging a foundation trench) is usually sufficient to establish commencement and permanently secure the permission.
Yes, but the rules are tight. Two-storey rear extensions are allowed under PD only if: they project no more than 3m from the original rear wall; are no higher than the existing roof; sit at least 7m from any rear boundary; use matching external materials; don't include side-facing upper-floor windows (unless obscure-glazed and non-opening below 1.7m); and the house is not a flat, maisonette or in a designated area. Most two-storey extensions exceed one of these limits and need full planning permission.
Single-storey rear extensions under PD in 2026 can project up to: 4m from the original rear wall on detached houses, or 3m on semis and terraces. Under the extended "Larger Home Extension" PD rules, detached homes can go up to 8m and semis/terraces up to 6m — but this requires the 21-day neighbour consultation scheme via Prior Approval. Maximum eaves height is 3m; ridge height cannot exceed the existing house. The rules apply to the original house as built in 1948 (or when first constructed, if later).
Side extensions under PD must be: single-storey only; no more than 4m in height; no wider than half the width of the original house; use matching external materials; and sit within the side walls of the original property. Two-storey side extensions are specifically excluded from PD and always need planning permission. Houses on designated land (conservation areas, National Parks, AONBs, the Broads, World Heritage sites) cannot use side-extension PD rights at all.
The Prior Approval (Larger Home Extension) process takes 42 days in total: a 21-day neighbour notification period followed by up to 21 days for the council to determine whether Prior Approval is needed. If no neighbours object and the scheme meets the rules, you can start work after day 21. If an objection is raised, the council must formally assess impact on neighbours — adding another 3 weeks. Council application fees are £120–£260. Budget 8–10 weeks from submission to confirmed start on site to be safe.
Sources & Further Reading

Our sources for this guide

Every figure in this guide is cross-referenced against primary UK sources. We cite the specific documents and data providers we used so you can verify and dig deeper.

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This guide was researched, written and fact-checked by the BestBuilders Editorial Team. Every figure is cross-referenced against primary UK sources (gov.uk, Ofgem, RICS BCIS, FMB, MCS), verified quote data from vetted contractors on our platform, and independent industry reports. Guides are reviewed at least quarterly to reflect current market conditions and regulations.

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UK-based · Reviewed 20 April 2026
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