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House extension design and planning guidance for London homes

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Permitted Development Rights for House Extensions

Some house extensions can be built without a full planning application. However, permitted development rights are subject to strict limits and conditions, and they do not apply equally to every property.

Not every house extension requires a full planning application.

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Some projects can be built under permitted development rights, provided that the proposal remains within the relevant limits and conditions.

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Permitted development can be a useful route for homeowners planning a rear extension, side extension or other improvement to a house.

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However, the rules are not always straightforward.

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The correct answer will depend on the original property, the location of the extension, its height and depth, the relationship with the boundaries and any restrictions affecting the home.

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It is important to check the position properly before building work begins.

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What Is Permitted Development?

 

Permitted development rights allow certain types of building work to proceed without submitting a standard planning application.

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The principle is simple: smaller or more limited home improvements should not always need the same formal planning process as a larger or more sensitive development.

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However, permitted development does not mean that anything is allowed.

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The work must remain within the relevant rules.

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If the proposal falls outside those limits, a planning application will normally be required.

Does Permitted Development Apply to Every Property?

 

No.

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Householder permitted development rights generally apply to houses.

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They do not normally apply in the same way to:

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  • Flats

  • Maisonettes

  • Apartments

  • Some converted properties

  • Some homes created through a previous change of use

  • Listed buildings

  • Properties affected by planning conditions

  • Homes where permitted development rights have been removed

  • Properties affected by an Article 4 direction

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A ground-floor flat may have a private garden and appear suitable for an extension, but a planning application will usually still be required.

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Similarly, a modern house on a newer development may be subject to a planning condition that restricts or removes some permitted development rights.

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The planning history should be checked before relying on the permitted-development route.

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What Is the Original House?

 

Many permitted-development limits are measured from the original house.

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This generally means the house as it was first built or, for an older property, as it stood on 1 July 1948.

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This matters because extensions added by previous owners may already have used part of the permitted-development allowance.

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For example, a home may have an existing rear addition or side extension that was built many years ago.

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Even if you did not build it, the previous extension may affect what can now be added without a planning application.

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The relevant starting point is not necessarily the property as it looks today.

General Rules for House Extensions

 

A proposed extension must satisfy several general requirements before it can qualify as permitted development.

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As a broad guide:

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  • The extension must not be built forward of the principal elevation of the house

  • The extension must not be higher than the highest part of the existing roof

  • The eaves must not be higher than the existing eaves

  • Where the extension is within two metres of a boundary, its eaves height must not exceed three metres

  • The external materials should normally be similar in appearance to the existing house

  • The extension must not include a veranda, balcony or raised platform

  • The total area covered by extensions and other buildings must remain within the permitted limit

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The detailed position should be checked against the specific proposal.

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The 50% Rule

 

Extensions and other buildings should not cover more than half of the land around the original house.

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This calculation can include:

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  • Existing extensions

  • New extensions

  • Detached garages

  • Sheds

  • Outbuildings

  • Other structures within the curtilage

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The area occupied by the original house is not included in the calculation.

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This rule is particularly relevant where a property already has several additions or a relatively small garden.

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A homeowner may have enough physical space to build an extension but still fall outside the permitted-development limits.

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Single-Storey Rear Extensions

 

Single-storey rear extensions are among the most common projects built under permitted development rights.

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Under the standard limits, a single-storey rear extension must not normally project beyond the rear wall of the original house by more than:

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  • Four metres for a detached house

  • Three metres for any other house

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The extension must not exceed four metres in overall height.

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Additional restrictions may apply where the site is within designated land, such as a conservation area.

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A modest rear extension may therefore be possible without a full planning application, provided that all the relevant conditions are met.

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Larger Single-Storey Rear Extensions

 

Some larger rear extensions may still be possible under permitted development rights using the prior-approval process.

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This route can apply where the proposed single-storey rear extension projects beyond the original rear wall by:

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  • More than four metres and up to eight metres for a detached house

  • More than three metres and up to six metres for any other house

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This is sometimes referred to as the larger-home-extension scheme or neighbour-consultation scheme.

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It is not an automatic permission.

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An application must be submitted to the local planning authority before work begins.

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The council will notify the adjoining neighbours.

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If concerns are raised, the council will consider whether the proposal would have an unacceptable effect on neighbouring amenity.

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The prior-approval route only applies in specific circumstances.

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It should not be confused with a normal householder planning application.

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Side Extensions

 

A side extension may qualify as permitted development in some circumstances.

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Where the extension projects beyond a side elevation of the original house, it must normally:

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  • Be single storey

  • Be no more than four metres high

  • Be no wider than half the width of the original house

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Side extensions on designated land will normally require a planning application.

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This includes conservation areas and certain other protected locations.

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A double-storey side extension will also require a planning application.

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Side-Return Extensions

 

A side-return extension uses the narrow area alongside the rear addition of a traditional terraced or semi-detached house.

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These projects are common in Victorian and Edwardian homes.

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Whether a side-return extension qualifies as permitted development depends on the shape of the original house and the precise footprint of the proposed addition.

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The position can become more complicated where the proposal extends beyond both a rear wall and a side wall of the original house.

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The total depth, width and relationship with the original house must be assessed carefully.

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A side-return extension should not be assumed to qualify automatically.

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Wraparound Extensions

 

A wraparound extension combines a rear extension with a side-return extension.

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It can create a large kitchen, dining and family space, but it often falls outside the permitted-development limits.

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This is because the proposal may extend beyond both the rear and side elevations of the original house and exceed the relevant width or depth restrictions.

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In many cases, a wraparound extension will require a householder planning application.

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This does not mean that it is unacceptable.

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It simply means that the council will need to assess the design through the formal planning process.

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Double-Storey Rear Extensions

 

Some double-storey rear extensions may qualify as permitted development, subject to strict limits and conditions.

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As a broad guide:

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  • The extension must not project more than three metres beyond the rear wall of the original house

  • It must not be within seven metres of the rear boundary

  • The roof pitch should match the existing house as far as practicable

  • Upper-floor side windows must normally be obscure-glazed and restricted from opening below the relevant height

  • The proposal must comply with the wider permitted-development rules

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Double-storey rear extensions on designated land will normally require planning permission.

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All double-storey side extensions require a planning application.

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Because upper-floor extensions can affect neighbouring properties more significantly, it is sensible to take advice before relying on permitted development rights.

What Is Designated Land?


Some permitted-development rights are more restricted on designated land.
 

This can include:
 

  • Conservation areas

  • National Parks

  • Areas of Outstanding Natural Beauty

  • The Broads

  • World Heritage Sites

  • Certain other protected areas
     

For most London and Home Counties homeowners, the most common issue is a conservation area.
 

An extension may still be possible, but the permitted-development route can be narrower.
 

For example, side extensions on designated land normally require a planning application.
 

The local planning context should be checked before the design is finalised.

 

What Is an Article 4 Direction?


An Article 4 direction is a local restriction that removes some or all permitted development rights within a defined area.
 

These directions are often used where the council wants greater control over alterations that could affect the character of a neighbourhood.
 

An Article 4 direction may apply to:
 

  • External alterations

  • Windows and doors

  • Roof changes

  • Front elevations

  • Cladding

  • Extensions

  • Other property improvements
     

The precise restrictions vary.
 

A home may therefore be located in an area where a project that would normally be permitted requires a planning application.

 

Can Permitted Development Rights Be Removed from an Individual House?


Yes.
 

Permitted development rights may be restricted by a condition attached to an earlier planning permission.
 

This is particularly common on some modern housing developments, where the council may want to retain control over later extensions or alterations.
 

The restriction may also result from the planning history of the property.
 

Before relying on permitted development rights, it is sensible to check:
 

  • The council’s planning records

  • Previous planning permissions

  • Any planning conditions

  • Whether an Article 4 direction applies

  • Whether the property is listed

  • Whether the property is in a conservation area

     

Does Permitted Development Apply to Listed Buildings?


Listed buildings require particular care.
 

The normal permitted-development position may be restricted, and listed-building consent may be required for work that affects the character or special interest of the property.
 

This can apply to internal as well as external alterations.
 

An extension to a listed building should be approached as a specialist design and heritage project.
 

Do not rely on general permitted-development rules without obtaining appropriate advice.

 

Do I Need to Tell the Council?


For some smaller projects, there may be no requirement to make a standard planning application.
 

However, this does not mean that it is always sensible to proceed without any paperwork.
 

For larger single-storey rear extensions using the prior-approval route, an application to the local authority is required before work begins.
 

For other permitted-development projects, a Lawful Development Certificate is often worth considering.

 

What Is a Lawful Development Certificate?


A Lawful Development Certificate provides formal confirmation from the local planning authority that the proposed work is lawful.
 

It is not the same as planning permission.
 

Instead, the council considers whether the proposal falls within permitted development rights or otherwise does not require planning permission.
 

A Lawful Development Certificate can be useful because it creates a clear planning record.
 

This may help:
 

  • Before construction begins

  • When selling the property

  • When remortgaging

  • When answering questions from solicitors

  • Where neighbours may raise concerns

  • Where the permitted-development rules are not completely straightforward

  • Where a builder wants confirmation before starting work
     

The application will usually need drawings and supporting information explaining why the proposal is lawful.
 

A certificate is not compulsory in every case, but it is frequently a sensible precaution.

 

Is Permitted Development the Same as Planning Permission?


No.
 

Planning permission involves the council assessing whether a proposed development is acceptable.
 

Permitted development rights provide an alternative route for specific types of work that meet defined limits and conditions.
 

A Lawful Development Certificate can confirm that a proposal qualifies under those rules.
 

The distinction is important.
 

A homeowner should not describe a project as “approved” simply because they believe it falls within permitted development rights.
 

The position should be checked and documented properly.

 

Do I Still Need Building Regulations Approval?


Usually, yes.
 

Permitted development relates to the planning position.
 

Building Regulations deal with the technical design and construction of the extension, including:
 

  • Foundations

  • Structural stability

  • Insulation

  • Drainage

  • Ventilation

  • Fire safety

  • Glazing

  • Electrical work

  • Heating

  • Materials and workmanship
     

Most house extensions still require Building Regulations approval even where planning permission is not needed.
 

Depending on the project, you may also need structural calculations, Building Control inspections and a completion certificate.

 

What About the Party Wall Act?


Permitted development does not remove the need to consider Party Wall matters.
 

The Party Wall etc. Act 1996 may still apply where the work includes:
 

  • Excavation close to a neighbouring building

  • New foundations below the level of a neighbour’s foundations

  • Building on or close to a boundary

  • Cutting into a shared wall

  • Inserting steel beams into a party wall

  • Raising or altering a shared wall
     

Planning permission, permitted development, Building Regulations and Party Wall matters are separate issues.
 

Each should be checked independently.

 

What If My Neighbour Objects?


For an extension that falls fully within permitted development rights, a neighbour cannot normally require a standard planning application simply because they dislike the proposal.
 

However, the work must genuinely satisfy the permitted-development rules.
 

For a larger single-storey rear extension using the prior-approval route, adjoining neighbours will be consulted.
 

If concerns are raised, the council will consider the potential effect on neighbouring amenity before deciding whether the extension can proceed.
 

Good communication with neighbours remains worthwhile in either case.

 

What Happens If I Get It Wrong?


Building an extension on the assumption that it is permitted development can create difficulties if the proposal later turns out to require planning permission.
 

This may lead to:
 

  • Planning enforcement issues

  • Delays

  • Retrospective applications

  • Design changes

  • Additional professional fees

  • Problems when selling the property

  • Questions from solicitors or mortgage lenders

  • Disputes with neighbours

  • Alterations to completed building work
     

It is far better to clarify the planning route before construction begins.

 

Check the Position Before You Build


Permitted development rights can provide a useful route for many house extensions.
 

However, the rules are detailed and the position depends on the individual property.
 

A small rear extension may qualify relatively easily.
 

A side-return extension, wraparound extension or project involving an unusual house layout may need more careful review.
 

The aim is not simply to avoid a planning application.
 

The aim is to choose the most appropriate route for the project and create a clear record before building work begins.

 

Find Suitable Extension Professionals


Depending on the project, you may need architectural design support, planning advice, Building Regulations drawings, structural calculations, Building Control input, Party Wall advice and an experienced extension builder.
 

Tell us a little about your home, the extension you are considering and the stage you have reached. We can help connect you with suitable professionals for the next steps.

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