Complete Guide to House Extension Planning Permission in 2026: Everything You Need to Know

Last updated: July 2026 · Verified against current government planning rules and North London council records.

Do you need planning permission for a house extension?

Quick answer: Often not. Most single storey rear extensions in England are permitted development, so no planning application is needed if you stay within the limits — 3m deep on a terraced or semi-detached house, 4m on a detached one, or up to 6m/8m with prior approval. Where you do need permission, the householder application fee is £548 (from 1 April 2026) and the statutory decision period is eight weeks from validation.

This guide covers both routes as they stand in July 2026: the permitted development rules that let you build without an application, and the full planning process — fees, timelines and council specifics for Barnet, Enfield, Haringey and the Hertfordshire border — when you need one. Every figure below is checked against the Planning Portal's current fee schedule and government planning statistics, because the fees changed again this April and plenty of older guides are now wrong.

Which extensions need planning permission? The decision table

Extension type	Planning permission needed?	Notes
Single storey rear, up to 3m (terrace/semi) or 4m (detached)	No — permitted development	Max height 4m; eaves max 3m within 2m of a boundary
Single storey rear, up to 6m (terrace/semi) or 8m (detached)	No, but prior approval required	£249 neighbour consultation via the larger home extension scheme
Double storey rear, up to 3m deep	No — permitted development	Only if it stays at least 7m from the boundary opposite the rear wall
Single storey side extension	No — permitted development	Max half the width of the original house, max 4m high
Two storey side extension	Yes	Falls outside permitted development
Wraparound (side + rear combined)	Yes, usually	The combined footprint typically fails the PD tests
Anything forward of the front elevation	Yes	Front extensions and porches over PD limits always need an application
Flat or maisonette	Yes — always	Householder PD rights apply to houses only
Conservation area or Article 4 street	Often yes	Side extensions and the 6m/8m scheme are removed on designated land
Listed building	Yes, plus listed building consent	Two separate consents needed

The last three rows catch North London homeowners out most often. Many streets across Barnet, Enfield and Haringey sit inside conservation areas or carry Article 4 directions that strip away specific permitted development rights, so an extension that needs no application one road over can require a full application on yours. Lofts and outbuildings follow their own rulebooks — see our guides on loft conversion planning permission and garden room planning permission.

Understanding House Extension Planning Permission in 2026

The planning system balances the needs of individual homeowners with broader community interests. Planning authorities consider impact on neighbouring properties, conservation of the local environment, and compliance with the local development plan. Each local authority has its own planning policies and priorities — Barnet, Enfield and Haringey each publish their own — which is why local knowledge matters when navigating these requirements. Understanding whether your project needs permission is essential because approval forms the legal foundation for the entire build. Extend without permission when you needed it and you face enforcement action, difficulty selling the property, and the cost of correcting or removing unauthorised work.

What are the permitted development limits for a single storey extension?

Permitted development is a standing national permission granted by the General Permitted Development Order. For a single storey rear extension it applies when all of the following hold: the extension projects no more than 3m beyond the original rear wall (4m on a detached house), the overall height stays within 4m, the eaves stay within 3m where the extension comes within 2m of a boundary, materials are of similar appearance to the existing house, and extensions plus outbuildings cover no more than half the land around the original house. "Original" means the house as first built or as it stood on 1 July 1948 — previous extensions eat into your allowance even if a former owner built them.

What are the rules for a double storey extension?

Two storey rear extensions can still be permitted development, but the rules tighten considerably. The extension must project no more than 3m beyond the original rear wall, must sit at least 7m from the boundary opposite that rear wall, and its roof pitch must match the existing house as far as practicable. Upper-floor side-facing windows must be obscure-glazed and non-opening below 1.7m. On designated land — conservation areas among it — rear extensions of more than one storey lose permitted development rights entirely. Most double storey extensions on North London's tighter plots fail the 7m boundary test, which is why the majority go through a full application. If you build up to or astride a shared wall, the Party Wall Act applies separately — our party wall agreement guide covers notices, surveyors and costs.

Is the larger home extension scheme still running in 2026?

Yes — permanently. The neighbour consultation scheme that allows 6m rear extensions on terraced and semi-detached houses (8m on detached) was made a permanent part of permitted development in May 2019 and remains in force in 2026. It is not a planning application: you submit a prior approval application (£249), the council notifies adjoining neighbours who have 21 days to object, and the council must determine the application within 42 days. If neighbours object, the council assesses only the impact on their amenity — not the design. If the council fails to notify you of a decision within 42 days, approval is deemed granted. The scheme does not apply on Article 2(3) designated land, including conservation areas. For the complete rulebook, see our permitted development rules 2026 guide.

How much does planning permission cost for an extension?

Planning fees in England rose 3.8% on 1 April 2026 under the annual CPI indexation introduced alongside the December 2023 fee reforms. The Planning Portal's April 2026 fee schedule lists the current figures:

Application type	Fee (England, from 1 April 2026)
Householder application (extension or alteration to a single house)	£548
Prior approval — larger home extension (6m/8m scheme)	£249
Prior approval — additional storeys	£249
Lawful Development Certificate — proposed works	£274
Lawful Development Certificate — existing works	£548
Removal or variation of a condition (householder)	£89
Non-material amendment (householder)	£46
Planning Portal service charge (fees over £100)	£91 inc VAT (£75.83 + VAT)

The service charge is added when you submit and pay through the Planning Portal; some councils still accept direct submissions, which avoids it. The application fee is only the start, of course. Professional design-and-planning fees typically run 8-15% of construction cost: a typical 25 square metre extension built at North London rates of £2,800-£4,200 per square metre (roughly £70,000-£105,000 — guide figures, not quotes) might carry design and planning fees of £5,600-£10,500, covering design development, the planning application, building regulations drawings and project management. Industry guides commonly estimate that well-designed extensions recover 70-90% of their cost in added property value — exact figures vary by street and specification, but the principle holds: cutting corners at design stage is a false economy. We keep a fee-by-fee breakdown, updated every April, on our extension planning fees page, and honest build-cost ranges on our North London extension cost guide.

Should I get a Lawful Development Certificate?

If your extension qualifies as permitted development, you are not required to apply for anything — but a Lawful Development Certificate (LDC) for proposed works, at £274 (half the householder fee), is money well spent. The council confirms in writing that your scheme does not need planning permission, and that certificate becomes priceless when you sell: solicitors and surveyors routinely ask for proof that extension works were lawful, and a missing certificate can stall a sale for weeks. An LDC also shuts down any later dispute with a neighbour who claims the build needed permission. Councils determine LDC applications within the same eight-week statutory period. If you have already built without paperwork, an LDC for existing works costs £548 and regularises the position — provided the work genuinely complied with the rules at the time.

Does permitted development mean I can skip building regulations?

No. Planning permission and building regulations are entirely separate approvals. Permitted development answers "am I allowed to build this?"; building regulations answer "is it structurally safe, fire-safe and properly insulated?". Every extension needs building regulations approval regardless of its planning status, covering foundations, structure, thermal performance, drainage and electrics. Building control fees for a typical extension run to several hundred pounds through your council or a registered building control approver (the private route that replaced approved inspectors in 2024), and the 2026 energy efficiency standards are noticeably stricter than a decade ago — your drawings must show compliance before work starts.

How long does planning permission take in 2026?

The statutory determination period for a householder application is eight weeks from validation. MHCLG's planning statistics for the year to March 2026 show councils decided 93% of householder applications within eight weeks or the agreed time — but note the second half of that sentence. Extension-of-time agreements are routine in London, so a realistic door-to-door expectation is 8-13 weeks. The first stage is validation, where the council checks your application is complete: councils aim for around five working days, though busy London boroughs can take longer, and an incomplete application goes to the back of the queue. Professional preparation that validates first time is the single cheapest way to save weeks.

Planning stage	Typical duration
Validation by the council	Around 5 working days
Neighbour consultation	21 days
Officer assessment and report	4-6 weeks
Total: submission to decision	8-13 weeks

After validation, the case officer consults internal departments — highways, environmental health, drainage — assesses neighbour representations, and prepares a recommendation. Nearly all householder applications are decided under delegated powers rather than by committee; only contentious cases with multiple objections tend to reach a committee agenda, which adds weeks. Applications involving heritage assets, protected trees or contested design points take longest.

How long do Barnet, Enfield and Haringey take to decide?

All three North London boroughs work to the same statutory eight-week target for householder applications. Enfield states it aims to decide householder and other minor applications within eight weeks of validation. In our experience across the three boroughs, straightforward householder applications on unconstrained streets do land within the statutory window, while conservation area applications, schemes attracting objections, and anything submitted during peak spring season commonly run to 10-13 weeks with an extension of time. All three councils offer paid pre-application advice, which is worth using for anything borderline — an officer's informal steer before submission regularly prevents a refusal after it.

Common planning challenges and how to overcome them

Three issues cause most extension refusals. First, design that fails to respond to local character: planning authorities, particularly in London conservation areas, are increasingly protective, and a scheme that ignores the prevailing rooflines, materials and rhythm of the street invites refusal. Careful analysis of the surrounding area and a design that is sympathetic while still delivering modern space is the answer. Second, harm to neighbour amenity — loss of light, privacy or overbearing visual impact. Designing around sightlines from neighbouring windows and positioning the extension to minimise shadow deals with most objections before they are made; early informal conversations with affected neighbours prevent the rest. Third, heritage constraints: listed buildings and conservation areas demand heritage impact assessment and specialist expertise, and applications that treat this as a box-ticking exercise get refused. In all three cases, pre-application consultation with the planning officer identifies concerns while the design can still change — which is precisely when changes are cheap.

Frequently asked questions

Do you need planning permission for an extension?

Not usually, for a single storey rear extension within permitted development limits — 3m deep on a terraced or semi-detached house, 4m on a detached one, up to 4m high. You need a full application for two storey side extensions, wraparounds, anything forward of the front elevation, all work to flats, and most schemes in conservation areas or on Article 4 streets.

How long does planning permission take?

Eight weeks from validation is the statutory target for householder applications, and government statistics show 93% are decided within eight weeks or an agreed extension. In Barnet, Enfield and Haringey, allow 8-13 weeks door to door, longer in conservation areas or where neighbours object.

What happens if I extend without planning permission?

You risk enforcement action requiring the work to be altered or removed, and serious difficulty selling the property, because planning approval forms the legal foundation of the project. Retrospective applications are possible but not guaranteed, and correcting unauthorised work afterwards costs far more than applying properly first time.

Is pre-application consultation worth doing?

Yes — informal discussions with planning officers before formal submission identify concerns early, allow design changes before you commit, and typically lead to smoother approvals with fewer amendment requests. All three North London boroughs offer a paid pre-application service.

How much do specialists charge for design and planning work?

Fees typically run 8-15% of construction cost. On a typical 25 square metre extension built at around £2,800 per square metre (about £70,000), that means £5,600-£10,500 covering design, planning, building regulations and project management.

What are the most common reasons extensions get refused?

Designs that ignore local character, harm to neighbour amenity (loss of light, privacy or overbearing impact), and unaddressed heritage constraints in conservation areas are the three most frequent causes of refusal.

Not sure which route your extension falls under? The Extension Company — the extensions studio of Pine Grove Design & Build Ltd, with 25+ years building across Barnet, Enfield, Haringey and the Hertfordshire border — checks your address against the latest council records before we design a thing, and every project carries our fixed-price promise so the number we quote is the number you pay. Get a feel for budget in 60 seconds with our extension cost estimator, or book a free site visit on 020 3051 9430.