House Extensions in North London: Planning Permission and Legal Requirements Explained

North London mixes Victorian terraces, converted flats, conservation areas and properties that have already been extended by a previous owner. That mix is exactly why the national rules rarely settle a question on their own. What follows is the framework, taken from the Planning Portal, GOV.UK, HSE and Citizens Advice, with the local checks flagged where they matter.

Two warnings before the detail. First, this is general planning information for England, not legal advice, and additional local rules may affect what permissions you need. Second, if you do not get a permission or approval you need, Citizens Advice notes you might be fined, prosecuted, or made to put things right or undo the work — and you might have problems when you sell.

Does permitted development apply to your property at all?

Permitted development rights are a general planning permission granted by Government rather than by your council. They let you extend a house without applying for planning permission, provided specific limits and conditions are met. But they do not apply to every home.

The Planning Portal is specific that the householder rules apply to houses only, and not to:

• flats and maisonettes;
• converted houses, or houses created through permitted development rights for changes of use, or under the ‘New Dwellinghouses’ rights in Part 20;
• other buildings.

They also do not apply where a planning condition, an Article 4 direction or another restriction limits or removes them. Houses and flats created through permitted development usually cannot then use householder permitted development for an extension, so planning permission is normally required.

One more definition decides most arguments: the rules are measured from the original house. That means the house as it was first built, or as it stood on 1 July 1948 if it was built before that date. You may not have extended it, but a previous owner may have done, and the rules apply to the total enlargement.

What permitted development allows for a rear extension

For single-storey rear extensions, the limit is measured beyond the rear wall of the original house: no more than four metres for a detached house, or three metres for any other house. A single-storey rear extension cannot exceed four metres in height.

Those figures only hold if the conditions that apply to all extensions are met as well:

• only half the area of land around the original house can be covered by extensions or other buildings;
• an extension cannot be higher than the highest part of the existing roof, or higher at the eaves than the existing eaves;
• where the extension comes within two metres of the boundary, the eaves height cannot exceed three metres;
• it cannot be built forward of the principal elevation or, where it fronts a highway, the side elevation;
• it cannot include verandas, balconies or raised platforms, a microwave antenna, a chimney, flue or soil and vent pipe, or any alteration to the roof of the existing house;
• materials used in exterior work must be of a similar appearance to those on the existing house;
• on Article 2(3) designated land the work cannot include cladding of the exterior.

Miss one of those and the project is no longer permitted development, whatever the depth figure says.

The larger single-storey extension route: prior approval

There is a separate, larger allowance. Where the property is not on Article 2(3) designated land or a Site of Special Scientific Interest, and subject to prior approval, the limit for single-storey rear extensions rises to eight metres for a detached house or six metres for any other house.

Prior approval is not the same as permitted development happening automatically, and it is not a full planning application either. It requires the local planning authority to be informed of the proposed work through a prior approval application so it can consider the proposal and its likely impacts. If a builder or designer quotes you the larger figures, ask whether they have allowed for that application and its timetable.

Side extensions and extensions of more than one storey

A side extension that would go beyond the side elevation of the original house cannot exceed four metres in height, can only be a single storey, and can only be up to half the width of the original house. On Article 2(3) designated land, all side extensions require householder planning permission.

For extensions of more than one storey, the rules tighten again. They must not extend beyond the rear wall of the original house by more than three metres, and must not be within seven metres of any boundary opposite the rear wall. The roof pitch must match the existing house as far as practicable, including where an upper storey is built on an existing extension. Any upper-floor window in a side elevation must be obscure-glazed and non-opening, unless the openable part is more than 1.7 metres above the floor.

All side extensions of more than one storey require householder planning permission. On Article 2(3) designated land, so do all rear extensions of more than one storey.

When you need householder planning permission

If you want to exceed the permitted development limits and conditions, it is likely that an application for householder planning permission will be required. Citizens Advice adds that you usually need planning permission for a major change to an existing building, such as adding an extension, and that you might also need it for smaller changes if you live in an area with extra planning restrictions.

You will usually pay a fee when you submit an application.

Lawful development certificates: proving you did not need permission

A lawful development certificate is not compulsory. It is the document you use when you want certainty that a proposal does not require planning permission, or that an existing use is lawful for planning purposes.

You apply to your local council and pay a fee. The application must provide sufficient information for the council to decide it, or it may be refused. The Planning Portal notes that the issues involved are often complex, and that you might benefit from professional advice; your local authority’s planning officers can also tell you what information is needed.

If your application is partly or wholly refused, is granted differently from what you asked for, or is not determined within the time limit of eight weeks, you can appeal to the Planning Inspectorate.

For a house you may want to sell later, a certificate is often worth the fee. It is much easier to produce than to reconstruct an argument about permitted development years afterwards.

Conservation areas, designated land and Article 4 directions

Article 2(3) designated land means land within a conservation area, an area of outstanding natural beauty, an area specified by the Secretary of State for the enhancement and protection of the natural beauty and amenity of the countryside, the Broads, a National Park, or a World Heritage Site. Several North London neighbourhoods fall into the first of those.

Separately, a local planning authority can issue an Article 4 direction removing some or all permitted development rights — for example within a conservation area, or within the curtilage of a listed building. Where one applies, you have to submit a planning application for work that would normally not need one. Article 4 directions are most common in conservation areas, and you can check with the local planning authority if you are not sure whether your property is affected.

Listed buildings sit under further consent requirements beyond the scope of this guide. Citizens Advice advises checking with your local council before doing any work on a listed building, and notes you might need listed building consent alongside planning permission or building regulations approval. Trees can be protected too, by a tree preservation order or by conservation area rules, so check before any tree work including pruning.

Building regulations approval is separate from planning

Building regulations approval is different from planning permission, and you might need both. GOV.UK states that plainly, and the Building Regulations 2010 cover the construction and extension of buildings.

Approval comes from a building control body. You can use either your local authority’s building control department or a private registered building control approver. If you use someone registered with a competent person scheme, you do not need to get approval yourself for the work that scheme covers — but building an extension is not covered, so you will still need a building control body. Citizens Advice adds that you will need to apply either for ‘full plans’ approval or by using a ‘building notice’, and that fees are usually payable both on application and on inspection.

The penalties are worth stating. The person doing the work could be prosecuted and fined for not complying with building regulations. The relevant building control body could make you pay to fix faulty work. And without approval you will not have the certificates of compliance you may need when you want to sell your home.

GOV.UK also notes that from 1 October 2026, applications for building control approval and initial notices for certain residential buildings may be subject to a tax called the Building Safety Levy. Whether that applies to a particular project is a question for your building control body; do not assume it does or does not apply to a house extension.

Party walls: telling your neighbours

This is a duty, not a courtesy. GOV.UK states that you must tell your neighbours if you want to carry out any building work near or on your shared property boundary, or party wall, in England and Wales.

A party wall stands on the land of two or more owners and either forms part of a building or does not — a garden wall counts, a wooden fence does not. A wall on one owner’s land that other owners use to separate their buildings is also a party wall. You can also have a party structure, such as a floor separating parts of a building with different owners, which is common in converted flats.

Party wall agreements are different from planning permission and from building regulations approval. Read the GOV.UK party wall guidance early, and if a neighbour does not agree, take advice from a party wall surveyor rather than pressing on. Neighbour response time is outside your builder’s control, which is why it belongs early in the extension timeline rather than the week before work starts.

Leasehold, freehold, covenants and your mortgage

Planning is not the only permission you may need. Citizens Advice advises checking whether your home is freehold or leasehold, and then checking:

• Leasehold: read the lease. You may need permission from the freeholder or the building’s management company before work starts.
• Freehold: your title register or deeds may contain covenants — legal promises not to do something, not to do it without someone else’s permission, or to do something. Your solicitor should have told you about them when you bought. Get legal advice if you are unsure what they mean.
• Mortgage: check your conditions. You might need to tell your lender about work you plan to do.

Permission may also be needed from the original property developer or a management company. None of these are planning matters, and none of them are checked by the council.

Community Infrastructure Levy on larger extensions

The Planning Portal notes that if the work adds over 100 square metres of floor space, it may also be liable for a charge under the Community Infrastructure Levy. That threshold is reachable on a substantial wraparound or double-storey scheme, so confirm the position with your borough before you set a budget.

Who holds the health and safety duties on your project

Under the Construction (Design and Management) Regulations 2015, a domestic client is anyone having construction work carried out on their own home, or a family member’s home, that is not done as part of a business. HSE explains that client duties for domestic clients normally pass to somebody else:

• to the contractor on a single-contractor project, who takes on the client’s legal duties in addition to their own;
• to the principal contractor where there is more than one contractor. If no principal contractor has been appointed, the client duties must be carried out by the contractor in control of the construction work.

If you appoint an architect or other designer on a project involving more than one contractor, you can ask them to manage the project and take on the client duties instead. They then take on the responsibilities of principal designer, and must have a written agreement with you confirming it. Without that written agreement, those client duties pass automatically back to the principal contractor.

Ask, in writing, who holds them on your job. It is a short question with a clear answer, and the answer tells you a lot about how organised the team is.

Choosing a builder who can work with this

No builder can influence a planning decision, and you should be wary of anyone who implies otherwise. What a good builder can do is prepare and coordinate accurate information, sequence the approvals so they do not collide with the build, and tell you plainly what is and is not within their control.

Check them the way Citizens Advice, TrustMark and HSE suggest: contactable references for comparable work, written quotes rather than estimates, proof of the insurance that applies to your project, a written contract with an agreed payment schedule, and a clear answer on the CDM 2015 duties. Our guide to how to choose a house extension builder in London works through each of those in order.

What this means for a North London project

Three practical consequences. First, borough variation is real: the national rules set the framework, but conservation area boundaries, Article 4 directions and local validation requirements are decided locally, so the council is the authority on your address, not a guide like this one. Second, terraces and semi-detached houses hit the three-metre single-storey limit and the party wall duty far sooner than detached properties do, so both belong at the start of the programme. Third, many North London houses have already been extended, and the measurement runs from the original house, so the remaining allowance may be smaller than it looks.

If you are not sure where your property stands, contact your local planning authority before any work begins. They can tell you whether the development may not be permitted and whether you need to apply for permission for all or part of the work. Note that councils may charge a fee for pre-application advice.

How BCS supports the process

We prepare and coordinate the information a planning or permitted-development route needs, and we keep the process moving where it is within our control. Whether a project needs householder planning permission, falls within permitted development, or is worth confirming with a lawful development certificate depends on the property, so we check that position first.

We build to the applicable building regulations and coordinate inspections with building control; the formal inspection and sign-off process remains with the appointed building-control body. We agree a project-specific programme once the scope and site conditions are clear. The planning decision itself belongs to the local planning authority, and we will tell you what we can influence and what we cannot.