Planning · Permitted development

Which route does your project need? Permitted development, prior approval, a lawful development certificate or full planning permission, compared for London houses with fees, timings and real projects.

Last updated 12 October 2026 · AURA Architecture & Interiors, RIBA Chartered practice

The figures here are approximate and meant to give you an idea, not a quote. Every house and brief is different, so your costs and programme will depend on your project.

Planning permission vs permitted development: what’s the difference?

Permitted development is a right granted nationally: if your house and project meet fixed limits, you build without applying. Planning permission is a decision your council makes on the merits of a specific design. Between them sit two halfway routes: prior approval for a larger rear extension, and a lawful development certificate that confirms a scheme is PD.

Fees are proposed to change on 8 December 2026 (householder £575, prior approval £310), subject to Parliament. A listed building also needs listed building consent.

The rules for houses sit in the General Permitted Development Order 2015, Schedule 2, Part 1. Each kind of work has its own class:

• Class A: extensions to the house (rear, side, and more than one storey)
• Class B: roof additions, such as a rear dormer or hip-to-gable
• Class C: other roof alterations, such as rooflights
• Class D: porches
• Class E: outbuildings, garden rooms and decking
• Class F: hard surfaces, such as a front driveway

Every limit is measured from the “original” house. That means the house as it stood on 1 July 1948, or as it was first built if it’s newer. Extensions added by earlier owners count against your allowance, which matters on Victorian and Edwardian houses that already have a kitchen extension.

The tests are different in kind. A planning application is judged on design, neighbours and local policy. PD is judged only on whether the scheme fits the written limits, so a design a council wouldn’t love can still be lawful, and a modest design that misses one limit by 10cm isn’t.

Which route for which project on a London terrace?

On a London terrace, most single-storey rear extensions, rear dormers within 40m³, rooflights and garden rooms can be permitted development. Wraparounds, two-storey rear extensions, front dormers and anything in a conservation area usually need planning. The table gives the official limit for each common project and what usually tips it into an application.

A few traps catch London houses more than any others.

A side infill is judged twice. It counts as a side extension (single storey, half the house’s width) and as a rear extension (3m, or 6m with prior approval, from the original rear wall). We compare the two layouts in our guide to choosing between a side return and a wraparound.

Lofts are counted, not judged. The 40m³ on a terrace includes any earlier roof addition, so a previous small dormer reduces what’s left. An end-of-terrace house counts as a terrace house, and a semi gets 50m³. No dormer or roof extension can go on a front roof slope that faces the road.

The mansard question. The rules never mention mansards. A full mansard usually raises the party wall line and changes both slopes, and anything that extends a front slope facing the road or rises above the existing ridge isn’t PD. In practice, almost every London mansard goes through planning.

Front means front. Extensions can’t go beyond the principal elevation, or beyond a side wall that faces a road. On a corner house, that rules out a lot of the side.

How long does permitted development take?

Pure permitted development has no application, so there’s no council wait: you can start once the design, building regulations and party wall notices are ready. A larger rear extension needs prior approval, decided within 42 days. An optional lawful development certificate has an 8-week statutory period. A householder planning application has an 8-week target.

The design stage on our project pages runs approx. 4 to 5 months and covers design, the planning route and technical drawings. It depends on your project.

The council clock is rarely the longest part. Party wall notices for work to a shared wall need at least 2 months before the start date, and a neighbour has 14 days to reply. If you serve them while the design is being finished, they run alongside everything else.

The 42 days for prior approval counts from the day the council receives your information. The 8 weeks for a certificate and for a householder application both start the day after the application is received. Councils can agree a longer period with you in writing, and in April to June 2026, 92% of householder applications in England were decided within 8 weeks or the agreed time.

You’ll sometimes see 13 weeks quoted. That’s the period for major development, such as larger housing schemes. It doesn’t apply to an extension or loft on your house. If you’re going through a full application, our guide on how long planning permission takes covers each stage in detail.

How does prior approval for a larger home extension work?

Prior approval lets a house outside a conservation area build a single-storey rear extension up to 6m deep (8m if detached) without full planning permission. The council notifies adjoining neighbours, who get at least 21 days to comment, then decides within 42 days. The fee is £249, proposed to rise to £310 from 8 December 2026, subject to Parliament.

The route has been permanent since May 2019. The extension must still meet every other Class A limit: single storey, max 4m high, eaves no higher than the existing eaves, and within the 50% coverage rule.

What the council can judge. If no neighbour objects, the council doesn’t need to assess the effect on neighbours. If one does, it judges the impact on the amenity of all adjoining premises, not only the neighbour who wrote in. Design merit and local policy aren’t part of the test.

When it can say no. The council can refuse if the scheme breaks a limit, or if you haven’t given enough information to show it complies. A refusal can be appealed like any planning refusal. Clear drawings with every dimension measured from the original rear wall save a lot of back and forth.

The 42-day rule and its catch. You can’t start until you have a written decision or 42 days have passed with no reply. Silence only helps a scheme that genuinely fits the limits. If it breaks one (too wide, too high, too much of the garden covered), it was never PD, and day 42 doesn’t change that. Keep dated proof of when the council received your submission.

Build what you described. The extension must be built as approved, or as described in your submission if the council didn’t reply. Changing the depth or roof on site takes you outside the route.

Prior approval isn’t available on what the rules call “Article 2(3) land”: conservation areas, National Parks, Areas of Outstanding Natural Beauty, the Broads and World Heritage Sites. There, the standard 3m (4m detached) is the PD limit, and anything deeper needs planning permission.

Should you get a lawful development certificate?

We’d recommend a lawful development certificate whenever a PD scheme sits close to a limit, the house has earlier extensions, or you expect to sell or remortgage. It costs £274 for proposed works, with an 8-week statutory period. For clear-cut work well inside the limits, such as rooflights or a small garden room, we’d usually skip it.

A certificate for proposed works (a section 192 certificate) answers one legal question: would this be lawful? The council doesn’t weigh design or local policy, and the law doesn’t require it to consult neighbours. Once it’s issued, the work is presumed lawful unless something relevant changes before you build. If the council misses the 8 weeks, you can appeal, as the Planning Portal’s certificate guidance explains.

When we’d recommend one:

• A side infill near the half-width line. A few centimetres decide it, and the original house’s width is taken at its widest point.
• A loft close to 40m³ (or 50m³). Volume calculations on old roofs with earlier additions are easy to get slightly wrong.
• Earlier extensions on the house. Whether the kitchen extension is “original” changes your allowance, and a certificate settles it.
• A sale or remortgage within a few years. A certificate is a single council document that answers the question.
• A worried neighbour or lender. It moves the conversation from opinion to a council decision.

When we’d usually skip it: rooflights within 150mm of the slope, a garden room clearly under 2.5m high near the boundary, or a 3m rear extension on a house with no earlier additions. The limits leave no real doubt, so the fee and 8 weeks buy little.

There’s a second type. A section 191 certificate confirms that something already built is lawful. It costs the full £548 fee, so it’s cheaper to ask the question before you build.

Conservation areas, Article 4 directions and flats: when permitted development doesn’t apply

Householder permitted development is reduced in conservation areas, can be removed street by street by Article 4 directions, and doesn’t apply to flats or maisonettes. Lambeth’s conservation areas alone cover about 30% of the borough, so check your address before you design anything. The council’s map and your house’s planning history give the answer.

What a conservation area removes. On Article 2(3) land, which includes every conservation area:

• all side extensions need planning permission
• any rear extension of more than one storey needs planning permission
• cladding in stone, artificial stone, pebbledash, render, timber, plastic or tiles isn’t PD
• roof extensions under Class B (dormers, hip-to-gable) aren’t PD
• the 6m and 8m prior approval route isn’t available
• outbuildings between the side wall and the boundary aren’t PD
• solar panels can’t go on a wall facing the road

A single-storey rear extension of 3m (4m detached) and rooflights can still be PD, unless an Article 4 direction says otherwise.

Article 4 directions. A council can remove specific PD rights for specific places. Where a direction applies, you apply for planning permission before doing the works it covers. Some cover a whole conservation area, others only part of it or only certain works, such as windows, doors, front boundaries or roofs.

Wandsworth’s conservation areas FAQ lists its directions, and notes that some cover only part of an area or only certain works.

Planning conditions. Rights can also be removed by a condition on an earlier permission for your house. You’ll only find it in the planning history.

Flats and maisonettes. Householder PD applies to houses only. A flat or maisonette, purpose-built or converted, has no PD for extensions or lofts, so every extension needs planning permission. It’s a full planning application rather than a householder one; the Planning Portal’s fee calculator gives the fee.

How to check your address. Look your house up on the council’s conservation area map, then its Article 4 list, then the planning history for your address. In Lambeth, the planning database search has a “constraints” tab that shows it in one place. A listed building also needs listed building consent, whatever the project.

If you need planning permission: what to expect

A householder application costs £548, has an 8-week target, and is usually granted: 91% were in England between April and June 2026. The council publicises it and neighbours can comment. Once approved, you have 3 years to start work. In return, planning can approve things PD never allows, such as a wraparound or a two-storey rear extension.

The fee is proposed to rise to £575 on 8 December 2026, subject to Parliament. Smaller works away from the house itself, such as an outbuilding, fence or wall that needs permission, cost £272.

Planning is often the route to more space. A full-width wraparound, a rear extension deeper than 6m, a two-storey rear on a short garden and almost every mansard can only happen this way. The council judges the design against its local policy, so the drawings and the planning case made for them matter.

PD sometimes gives more. Because it’s judged on volume and limits, not design policy, a loft on a semi with a hip-to-gable and full-width rear dormer can be larger under PD than a council’s design guidance might allow through planning. You can also combine routes: a PD loft and a planning-approved extension, for example, as long as each one meets its own rules.

If an application is refused, you can revise and resubmit, or appeal. The decision notice gives the council’s reasons, which is where a revised scheme starts.

Three AURA projects, three routes

The route follows the house and the street. Three of our projects show it: a garden office in Wandsworth built under permitted development, a kitchen extension and dormer loft in Wimbledon approved through planning, and a Putney house in a conservation area where even replacing windows needed consent.

Trinity Road, Wandsworth: a garden office under permitted development

An early-1900s house extended and restored across 8 split levels, with the existing basement extended to form a reception room, wine room, study and courtyard. The permitted development part is the outbuilding, designed as a garden office or yoga studio, with power, internet and lighting. It was built under permitted development, so the garden office didn’t need to go through planning. Design took 5 months and the build 18 months. If you’re thinking about a garden room, our guide to planning for a garden office goes through the outbuilding rules.

Wandsworth

What happens if you build without the right consent?

The council can invite a retrospective planning application or take enforcement action, which can require the work to be changed or removed. For works substantially completed on or after 25 April 2024, it has 10 years to act; for works completed before that date, the earlier 4-year limit still applies. Most problems are avoidable with checks before you build.

A retrospective application. The council can invite one, but approval isn’t automatic. If it’s refused, the council can issue an enforcement notice requiring you to put things back as they were. You get one chance to secure permission after the event, either through that application or through an appeal against the enforcement notice.

Enforcement is discretionary. Councils have discretion over whether to act. Options include an enforcement notice, a stop notice, or a breach of condition notice when an approved scheme wasn’t built as approved.

The time limits. Once the period has passed, the council can no longer enforce. That isn’t the same as permission. To record it formally, you’d apply for a certificate of lawfulness for existing development, at the full £548 fee, with evidence of the completion date.

How to avoid it, calmly:

• Check before you design. Conservation area, Article 4, planning conditions and earlier extensions, all from the council’s website.
• Measure from the original house. The limits run from the house as it stood in 1948 or as first built, so establish what’s original before drawing anything.
• Get a certificate where it’s close. For £274 and 8 weeks, a council decision replaces a judgement call.
• Build what you notified. For prior approval, keep the submission, the receipt date and any decision with the deeds.
• Keep the paperwork together. Certificates, approvals and building control completion certificates are what you’ll show a buyer.

Do you still need building regulations and a party wall agreement under permitted development?

Usually, yes. Permitted development covers planning only. Building regulations are a separate approval and usually apply to an extension or loft; your building control body will confirm. On a terrace or semi, party wall notices apply to work on a shared wall. In Thames Water’s area, building near a public sewer usually needs a build-over agreement.

Building regulations. Planning and building regulations ask different questions: planning is about what you build and where, building regulations about how it’s built (structure, fire, insulation, drainage). The gov.uk building regulations guidance is clear that you might need both. Our guide to what building control involves explains the choice of inspector and the stages.

Party wall notices. The Party Wall Act is separate from planning and building regulations:

• work to a party wall (cutting in steels, raising it for a loft): at least 2 months’ notice
• a new wall on the boundary line: at least 1 month
• excavating within 3m of a neighbour’s building and deeper than its foundations, or within 6m in some deeper cases: at least 1 month

A neighbour has 14 days to reply. If they don’t reply to a party wall or excavation notice, a dispute is treated as having arisen and surveyors are appointed. Surveyors’ fees are approx. £200 per notice and £900 to £2,000+ per award, depending on your project. Our guide to party wall agreements covers the process.

Thames Water build-over. In Thames Water’s area, building within 3m of a public sewer, or within 1m of where a pipe serving only your house crosses the boundary, usually needs a build-over agreement. The 2026 charges run from £130 to £585 depending on the sewer size, with legal costs from £1,000 on the largest, and they’re updated every April. Ask for the sewer map at the start of design, before the extension’s footprint is fixed.

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