Rear Extension Planning in London: 3m Limit, 6m Consultation
Most single-storey rear extensions fall under Class A permitted development, and larger ones can go through the neighbour consultation scheme. Standard limits are 3 m for most houses and 4 m for detached ones, with larger allowances of 6 m and 8 m subject to consultation. Two-storey, listed, conservation area and Article 4 cases usually need full planning permission. Building Regulations are always a separate requirement.
TL;DR:
Measure from the original rear wall, not a previous extension; existing additions count toward the allowance, and structural parts count while guttering does not.
Most houses have a 3 metre limit and detached homes 4 metres; neighbour consultation can raise those caps to 6 and 8 metres, respectively.
The local planning authority has 42 days to decide larger extension notices and assesses objections only for effects on light, privacy, and overbearing impact.
Extensions with two floors, listed homes, conservation area restrictions, and withdrawn rights may require full planning permission; Building Regulations approval remains separate.
Table of Contents
Permitted development rules for single-storey rear extensions
Larger single-storey extensions: how the neighbour consultation works
Choosing between prior approval, planning permission and a lawful development certificate
Building Regulations and other consents to check alongside planning
Your checklist and timeline: drawings, measurements and fees
Our perspective on planning and delivery in West and Central London
Permitted development rules for single-storey rear extensions
Class A permitted development covers enlargements of a dwelling house, and rear extensions sit squarely within it. Under paragraph A.1(f), a single-storey extension can go beyond the rear wall by no more than 4 metres on a detached house or 3 metres on any other house, with a total height of no more than 4 metres. Paragraph A.1(g) allows larger single-storey extensions, up to 8 metres for detached houses and 6 metres for others, but these are subject to the neighbour consultation scheme covered in the next section.
Measurement is where many homeowners trip up. You measure from the base of the original rear wall to the outer edge of the extension. The original means the house as it was originally built, not the house you bought. Guttering and barge boards are not counted, but everything structural is. In practice, a bay window or conservatory added by a previous owner may already have used up part of your allowance. We often start a site survey by finding the true original wall line, because a few hundred millimetres can change which route you need.
Cumulative enlargement is the second trap. Existing extensions count towards your total under paragraph (ja), so an existing rear addition leaves less room for a new one. For worked examples, our guide on permitted development extension limits walks through several layouts, and our broader overview of permitted development rules in the UK covers the other classes.
The limits only help if the continuing conditions are also met:
Materials must be of a similar appearance to the existing house.
The extension must not sit forward of a wall that fronts a highway.
The extension must not cover more than half the curtilage, counting all other buildings.
Eaves near a boundary must comply with the applicable height restrictions.
Side extensions are subject to restrictions on their height and width.
Rights do not apply on article 2(3) land (conservation areas and similar designated land) in the same way, and a property can have its rights removed altogether.
Larger single-storey extensions: how the neighbour consultation works
The neighbour consultation scheme is a form of prior approval for larger single-storey rear extensions. GOV.UK explains that you notify the local planning authority (LPA), which then consults your adjoining neighbours. If a neighbour objects, the LPA assesses the effect on their amenity and decides whether the work can go ahead. It applies when your extension projects beyond the standard 3 m or 4 m limit, up to the 6 m or 8 m maximum.
The sequence works like this:
You submit your notification through the Planning Portal, with a written description, the projection, the height and a site plan.
The LPA writes to the adjoining owners and occupiers, inviting them to comment.
If no neighbour objects, the development is permitted once the LPA confirms prior approval is not needed, and you can proceed.
If a neighbour objects, the LPA assesses the impact on amenity: loss of light, overbearing effect and privacy.
The LPA has 42 days from receipt to notify you of its decision. If it says nothing within that time, work can proceed.
The assessment is narrow. The LPA is looking at neighbour amenity, not whether it likes the design. That makes the scheme more predictable than a full application, but a reasoned objection from a next-door owner with a window facing your boundary can still lead to refusal.
A practical point we raise with clients: speak to your neighbours before the notice lands. A conversation, a sketch and an honest explanation of the projection and height usually do more than any drawing. Neighbours who feel informed tend not to object, and a clean consultation is the fastest route to a green light.
When you need a full householder planning application
Some projects never qualify for permitted development, and it pays to spot them early. You may need a householder planning application for a rear extension that does not qualify for permitted development.
The property is a listed building.
The house sits in a conservation area and the proposal exceeds what that designation allows.
An Article 4 direction removes your permitted development rights.
A planning condition on the original permission removed those rights.
Your works, added to earlier extensions, exceed the Class A limits.
An Article 4 direction is a tool a council uses to withdraw specific permitted development rights in a defined area, usually to protect local character. In plain terms, work that would normally be allowed automatically needs a formal application instead. GOV.UK notes that rights can also be removed by planning conditions or because of listed status, so always check the position for your specific address with the LPA before you commission drawings.
Across West and Central London, conservation areas are common, and many streets in Kensington, Chelsea, Notting Hill and Chiswick carry extra controls. A full application also lets the council weigh the design, scale and local character, which gives you the chance to make a positive case for the scheme on its merits. Proposals are judged on their impact on neighbours’ outlook and the street scene, so early design work matters.
Choosing between prior approval, planning permission and a lawful development certificate
Each route does a different job, and picking the right one saves time and money.
Prior approval (neighbour consultation): the LPA decides within 42 days, and the outcome confirms you can build under permitted development. It tests neighbour amenity only.
Householder planning application: the LPA assesses the full merits, including design, scale, materials and neighbour impact. Decision times vary, and fees are set nationally, so check the Planning Portal or your council’s fee schedule rather than relying on a rule of thumb.
Lawful development certificate: under sections 191 and 192 of the Town and Country Planning Act 1990, section 192 confirms whether a proposed use or operations would be lawful. It is legal confirmation of lawfulness, distinct from planning permission, and it does not assess planning merits.
Existing extensions: section 191 certificates cover existing use or development, which helps when you sell and a buyer’s solicitor asks for proof that an older extension was lawful.
A lawful development certificate is worth considering even where permitted development clearly applies, because it gives you a document to hand over later. None of these decisions replaces Building Regulations. A planning outcome tells you the building may go ahead; it says nothing about whether it is built safely.
Building Regulations and other consents to check alongside planning
Building Regulations approval is a separate process from planning. As GOV.UK sets out, you must comply with them even when permitted development or planning permission applies. Extensions are checked for structure, fire safety, insulation, ventilation, drainage and more. You choose the type of application, and the most thorough route typically gives a decision within 5 weeks, or 2 months with consent.
Other approvals to check before work starts:
Party wall awards: needed when you build on or near a shared boundary, or excavate close to a neighbour’s foundations.
Drainage and sewer connections: building over or near a public sewer usually needs the water company’s agreement.
Listed building consent: separate from planning permission, and required for any alteration to a listed property.
Community Infrastructure Levy (CIL): potentially payable on larger additions, depending on your council’s charging schedule.
Skipping Building Regulations sign-off tends to surface at the worst moment. A buyer’s solicitor spots the missing completion certificate, and you face retrospective regularisation, which may mean opening up finished work for inspection.
Your checklist and timeline: drawings, measurements and fees
A tidy submission moves faster. Work through these steps in order:
Commission a measured survey that fixes the original rear wall as your baseline.
Prepare the location plan and site plan showing the extension against boundaries.
Draw existing and proposed floor plans and elevations.
Write a clear description of the projection, height and materials.
Bring in a structural engineer where the design opens up the rear wall or needs new foundations.
Submit via the Planning Portal and pay the fee your council lists.
Speak to adjoining neighbours before the notices arrive.
Pro Tip: Photograph the rear of the house from several angles before any work, with a tape measure against the original wall, so the baseline is on record.
Expect prior approval to run to 42 days, with Building Regulations running in parallel. We always point clients to the council’s own fee schedule rather than quoting a figure, because fees change and vary by application type.
Technical documents you will be asked for
Your drawings and reports need to be specific. These are the usual requests:
Site plan: shows the extension’s position relative to boundaries and neighbours.
Floor plans and elevations: existing and proposed, with dimensions.
Sections: show heights, roof pitch and floor levels.
Structural calculations: needed for steel beams (RSJs) and foundation design, prepared by a structural engineer such as the team at Xponexus Engineering, who produce calculations for rear extensions and structural alterations.
Photographic record: the original rear wall before work begins.
Consider a lawful development certificate if you want sale protection later.
How a rear extension affects property value
A well-planned rear extension tends to be one of the more reliable ways to add usable space, particularly in London, where moving costs are high and plots rarely allow much expansion sideways. Buyers respond to a kitchen-diner that opens onto the garden, an extra bedroom or a proper family room, and these are often the rooms that decide a viewing.
The value you gain depends on location, quality and how well the new space connects with the old. A cramped addition that swallows the garden or blocks light into existing rooms can lose much of its appeal. We would also stress paperwork: buyers’ solicitors ask for planning evidence, a Building Regulations completion certificate and, where relevant, a lawful development certificate. Missing documents can delay or complicate a sale.
Rather than chasing a headline percentage, weigh what the space gives you to live with, then treat resale as a welcome extra. A good agent in your postcode can tell you how local buyers value an additional room.
Design considerations: style, materials and integration
Design decisions affect both how the extension looks and how smoothly it passes planning. Permitted development requires materials of a similar appearance to the existing house, so brick that matches the original bond and tone is the safe route. A full planning application gives more freedom, and contemporary glazed or timber-clad additions can work well when they sit confidently alongside a period house.
Think about how the old and new spaces join. Where you remove the rear wall, the structural opening, floor levels and threshold details determine how seamless the transition feels. Matching floor heights avoids awkward steps, and aligning the roofline with existing eaves keeps the proportions calm.
Light is the other big factor. Rooflights, glazed doors and corner windows can transform a deep plan, but they must respect neighbours’ privacy, particularly with side-facing glass near a boundary. Consider orientation too: a south-facing garden suits large glazing, while a north-facing one may call for roof lights to pull daylight into the middle of the plan.
Common challenges and how to solve them
Most delays trace back to a handful of issues, and each has a practical fix.
Unclear original wall line. Previous extensions can blur the baseline. A measured survey and old plans from the council’s records settle it before you design.
Neighbour objections. Early conversations, clear drawings and a willingness to adjust the height or projection often resolve concerns before they become formal objections.
Restricted rights. Article 4 directions, conservation areas and conditions can catch homeowners out. Check your property’s status with the LPA first.
Structural surprises. Opening up a rear wall can reveal poor foundations or unexpected drainage. A structural engineer’s early input and a survey of drains reduce the risk of costly changes mid-build.
Sequencing consents. Planning, Building Regulations and party wall notices overlap, and missing one can stall the others. A single timeline that tracks each approval keeps the project moving.
Where a scheme is borderline, we usually recommend a lawful development certificate or a householder application over assuming permitted development applies. Certainty costs less than rework.
Environmental and sustainability considerations
A rear extension is a good moment to improve the energy performance of the house, because the new structure must meet current Building Regulations for insulation and ventilation, and the junction with the old building is an opportunity to upgrade it. High-performance insulation, airtight detailing and good glazing keep running costs down.
Choose materials with care. Reclaimed or locally sourced brick, responsibly sourced timber and low-carbon insulation reduce the footprint of the build. Offsite options are worth a look as background too: modular extension systems use insulated panels assembled quickly, though suitability depends on the site and planning route.
Do not overlook water and green space. Permeable paving, a green roof over a flat extension and sensible drainage reduce run-off, and retaining garden planting helps wildlife and keeps the outlook pleasant. Planning officers often respond well to schemes that show thought in these areas, and they can strengthen a householder application where design is being judged.
The role of architects and planning consultants
An architect turns your brief into drawings that work for you, for the council and for the builder. They test layouts, advise on the best route (permitted development, prior approval or full application) and produce the plans the LPA needs. For a listed building or a conservation area, their experience with the local planning authority can be decisive.
A planning consultant steps in where the proposal is contentious: a two-storey extension close to neighbours, a site with a refused history, or an appeal. They frame the case against local policy and manage the dialogue with the planning officer.
Some homeowners go straight to a builder who can also handle drawings and submissions, which works well on straightforward schemes. The key is knowing who is responsible for what. Ask who prepares the measured survey, who submits the application, who liaises with the LPA and who carries responsibility if a decision goes against you. A clear division of tasks avoids gaps.
Choosing a reputable builder for a rear extension in London
Choosing the builder is as important as winning the permission. Start with evidence: completed rear extensions you can see, references you can call and a track record in your part of London, where tight access and terraced plots add complications.
Look for a fixed, itemised quotation after a site survey, not a verbal estimate. Check insurance cover and warranties, ask who will be on site daily and whether the work is done in-house or passed to a chain of subcontractors. Fewer handovers usually means fewer misunderstandings.
Ask how the builder handles Building Regulations inspections, party wall matters and neighbour relations, because these shape the experience as much as the brickwork. A builder who talks confidently about measurement rules, prior approval timelines and structural design is likely to run the build with the same care. Be wary of anyone who dismisses permissions as a formality.
Our perspective on planning and delivery in West and Central London
We have been building and refurbishing homes in London, including in Fulham, Chelsea, Kensington, Chiswick, Hammersmith and Notting Hill. Our director-led oversight means planning questions, drawings and site work are coordinated, which cuts the risk of building something that does not match what was approved. Use the checklist above, and book a site survey with us when you want a clear answer for your property.
— Mateja
Let us take your rear extension from site visit to handover
We handle the whole journey, so you deal with one team from first measurement to final snag. A site visit, measured drawings, your planning or prior approval submission, structural design and the full build with project management all sit under one roof, across West and Central London.
Site visit and measured survey of your original rear wall
Planning or prior approval submission prepared with you
Structural design and in-house build with director oversight
Book a site visit or request a quote through our extension service page, and see our dedicated rear extensions page.
FAQ
Can I build a 3m rear extension without planning permission?
In many cases, yes. Class A permitted development allows a single-storey rear extension of up to 3 metres on most houses, or 4 metres on a detached house, provided the other conditions are met. Check that your property has not lost its rights through an Article 4 direction, listing or a planning condition, and remember that measurement starts from the original rear wall.
How much does it cost to add a rear extension to a house in the UK?
The cost depends on size, structure, finish and location, so there is no single figure that fits every home. London projects tend to cost more because of access and labour. We provide an itemised quotation after a site survey, and price is available on request once we have seen the property.
Do you need planning permission for a back extension?
Not always. Smaller single-storey extensions often fall under permitted development, and larger ones use the neighbour consultation scheme. A two-storey extension, a listed building or a conservation area usually needs full planning permission, and GOV.UK guidance on when permission is required is the place to confirm your position.
What are the rules for building a two-storey rear extension?
A rear extension that does not qualify for the single-storey Class A allowances may need a householder planning application. The council will weigh design, scale and the effect on neighbours’ light and outlook. Building Regulations approval is also required.
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