Permitted development house extension showing timber framed rear extension and concrete beams

When extending your home its often assumed that you will need planning consent. However, not all development requires planning permission. In some instances, extensions are allowed under national permitted development rights.

This article discusses the benefits of designing a house extension that complies with permitted development (PD) legislation, as an alternative to seeking planning consent.

Rather than relying on the local authority to grant planning permission to extend your home, you may, in fact, be entitled to extend without planning approval at all.


Architecture for London has completed a number of permitted development house extensions in London. View Architecture for London’s portfolio of recent work, or contact us on 020 3637 4236 to discuss your project.

Building an extension without planning consent

If your extension falls within the national permitted development rights, then you can theoretically carry out the building works immediately, without planning consent.

The PD rules must be interpreted correctly and accurately to ensure that the building works comply. In the event of an extension not complying with the guidance then a local authority could issue an enforcement notice for demolition.

It is therefore best to confirm that the proposed works are permitted development prior to building. This can be done by applying for a ‘lawful development certificate’ (LDC).

Permitted development house extension

A house extension in Dartmouth Park finished in brick, concrete and timber.

Lawful development certificates

It is not compulsory to apply for and obtain a lawful development certificate to undertake permitted development works. An LDC simply gives certainty that the works you are undertaking do not need planning consent.

An LDC is also likely to be required by a future purchaser to confirm a house extension is lawful before any sale can complete.

The process of obtaining a LDC is similar to making a planning application. You make an application via the Planning Portal online, and then the local authority will process the application. Like planning applications for residential dwellings the local authority have 8 weeks to determine the application.

Why not just apply for planning?

The timeframes, application forms, and drawings required for LDC applications are similar to planning applications. The process is distinctly different however.

The main difference is the local authority will assess the application against permitted development rights, rather than planning policies; and whilst PD rights are often similar to local planning policy they are different and separate.


This is important as planning policies are often subjective, with qualitative requirements often being sought (e.g. “harmonious”, “in-keeping”, “not-detrimental”). In contrast, permitted development rights are typically quantifiable with clear and descriptive requirements set out (e.g. sizes, heights and volumes are clearly defined). Consequently permitted development is much less open to interpretation.

As planning policy is often more restrictive than permitted development rights, it is sometimes possible to carry out development that would otherwise be restricted by local planning policy.


The local authority may not wish for you to extend the back on your house, or build a roof extension to the size you want, yet you may be entitled to do so under permitted development rights. This may be possible if you meet all of the applicable criteria required under the relevant legislation.

Is permitted development faster?

As there is less subjectivity involved in assessing the submitted documents for permitted development, there is less risk involved in starting the next stage of work (technical design). Conversely, in the case of a full planning application it would be advisable to await for a decision before commencing the next project stage. This means that taking the PD route can help to reduce your programme, to get your build on site earlier.

Permitted development drawings loft calculation

There is less subjectivity in a PD application, and if the volumes can be proven, the works should be permitted. The volume calculations can become complex. This is illustrated in the above diagram for a rear outrigger, mansard loft conversion in Lambeth, south London. The total volume here was designed to be 39.93 cubic metres, to comply with the requirement for max. 40 cubic metres that may be added to an attached house under permitted development.

Permitted development rights

Permitted development rights derive from a general planning permission granted by parliament. The principal order that gives this right is The Town and Country Planning (General Permitted Development) (England) Order 2015.

The order outlines works that you can do without requiring planning permission. Schedule 2 of the order outlines Permitted Development Rights under 19 parts. Works to residential dwellings are mainly covered within Part 1 “Development within the curtilage of a dwellinghouse”, and Part 2 “Minor operations”.

Each part lists specific types of work under different classes, each of which then have a number of restrictions and conditions that must be met. The more substantial permitted development rights for residential extensions are contained within Part 1, Classes A to E as follows:

Part 1, Classes A to E

  • Class A – enlargement, improvement or other alteration of a dwellinghouse

Class A outlines the permitted development rights for rear extensions, side extensions and side infills, as well as general alterations such as adding new windows and doors.

Typically rear extensions are single storey and up to 3-4m in depth. But in certain situations it may be possible to extend up to 8m without planning permission. Two storey extensions are also covered, but these must be a minimum of 2m away from the boundary.

  • Class B & Class C – additions and alterations to the roof of a dwellinghouse

These classes provide the permitted development rights for roof extensions, re-roofing and adding rooflights.

Generally roof extensions must be to the rear and less than 40 cubic metres in size (i.e. additional external volume) for a mid terrace, or end of terrace property. This allowance increases to 50 cubic metres where detached or semi-detached.

  • Class D – porches

Small front extensions of up to 3 square metres are often permitted development when placed directly outside an external door.

  • Class E – buildings etc incidental to the enjoyment of a dwelling house

This class provides permitted development rights for outbuildings such as swimming pools. The main requirements are that the building must be detached, less than 50% of the garden, and not forward of the front of the house. There are different height restrictions depending on the proximity to the boundary.

Restrictions of permitted development

The above summarises some of the work that may be possible under permitted development rights, however there are a great number of restrictions and conditions under each class that must be followed.

Further restrictions also exist in certain areas and for certain buildings. This includes designated areas, listed buildings, and properties or areas where permitted development rights have been withdrawn. 

Similarly if any legal restrictions exist that may be associated with the land, these too will need to be adhered to. An appropriate legal professional will be able to provide further advice on this if necessary.

Non residential dwellings

Permitted development rights that apply to many common projects for houses do not apply to flats, maisonettes or other buildings. Commercial properties do have some PD rights but they are different to those granted to residential dwellings.

lawful development certificate house extension

A house extension in Dartmouth Park finished in brick, concrete and timber.

Listed buildings

A large number of permitted development rights do not apply to listed buildings.  Alterations to listed buildings or their curtilage usually require planning permission from the local planning authority. Even where permitted development rights do exist it may still be necessary to also seek listed building consent. 

Designated areas

In some areas of the country, known generally as ‘designated areas’ or Article 2(3) land, permitted development rights are also restricted. These include:

  • conservation areas
  • National Parks
  • Areas of Outstanding Natural Beauty
  • the Norfolk or Suffolk Broads
  • World Heritage Sites

If you live in one of these areas you will need to apply for planning permission for certain types of work that may be permitted development elsewhere.

Permitted development rights withdrawn

Some sites also have permitted development rights specifically removed. The local planning authority does this by issuing an ‘Article 4’ direction. This will mean that you have to submit a planning application for work that normally would be permitted development.

Article 4 directions are generally made when the character of an important area would be threatened. They are most common in conservation areas. You can check with the local planning authority to see if your property is affected.


Houses that have been created using permitted development rights (by changing the use from shops, financial and professional services premises or agricultural buildings) cannot use householder permitted development rights. Again, planning permission is usually required.

Even when some parts of a proposed house extension are not deemed permitted development, it may only be necessary to seek planning consent for these parts of the work, and still utilise permitted development rights for the rest of the work proposed.

Permitted development loft conversion

A modern loft conversion with ensuite bathroom in Islington, north London.

How big can I build an extension without planning permission?

The most common extension projects are single storey rear extension and roof extensions. Generally single storey rear extension up to 3m in depth, and roof extensions up to 40 cubic metres don’t require planning.

For a typical terrace house in London which is 5m wide this would be a rear extension of 15sqm which can extend and open up the family living, kitchen and dining spaces and connect these to the garden. A full width dormer roof extension should also be possible, which is often big enough to create a master bedroom in the roof space with en-suite and dressing area.

In theory, larger rear extensions of 6m and 8m are possible (attached and detached properties respectively). As of May 2019, this potential allowance for larger extensions has now been made permanent.


In order to build these larger extensions under permitted development the local authority must be notified. They will then consult the adjoining neighbours to advise them of your planned development.

If neighbours raise any objections then the local authority has the power to prevent your larger extension. This will be due to the impact on the amenity of neighbouring properties.

The reality of building a 6m deep rear extension to a terraced property in London is therefore slim. It would be rare to find a neighbour that did not object to this development. Perhaps the more isolated properties in London would have more chance of success with this approach.

As every site is different and there are a great number of complex and detailed class conditions and other restrictions it is impossible to outline every case.

Seek advice from an architect

Before undertaking work it is important to seek professional advice from an architect to check the work you wish to carry out is permitted development. It is advisable to obtain confirmation from the local authority that the works are deemed permitted development.

Even when a planning or PD application is not needed, any other consents required under other regimes will still be required. For example listed building consent, building regulations, and works to protected trees. These too will often require professional advice before undertaking the work. In Camden, we achieved planning consent for a large rear extension to a detached Victorian house. 

Drawbacks of permitted development

Usually there will be some restrictions on the proposed external materials under permitted development. Materials are typically required to be ‘similar’ to those used in the existing house, although the term ‘similar’ can be interpreted creatively by an experienced architect.

One potential issue often overlooked is that a lawful development certificate only confirms that the work would be deemed lawful if it were complete on the day of the certificate, unlike planning consent which gives you 3 years to commence the work.

Therefore if an LDC is received and then the PD rules are changed in a way that result in the works no longer being deemed to be PD, if the works haven’t been completed then technically they are not lawful. It is perhaps unlikely that the planning authority would enforce if the works were already started and they were completed in a reasonable time.

To view Architecture for London’s residential projects, including those completed under permitted development, please visit Architecture for London’s portfolio.

Permitted development FAQ

What size extension can you build under permitted development?

Typically single storey rear extensions can be up to 3-4m in depth. But in certain situations it may be possible to extend up to 8m without planning permission. Two storey extensions are also allowed, but these must be a minimum of 2m away from the boundary.

What is a certificate of lawfulness?

A certificate of lawfulness (or lawful development certificate) is similar to a planning approval. It is issued by the local authority to certify that a proposed extension complies with permitted development rules.

Can I build an extension without planning consent?

Permitted development rights normally exist for freehold houses, these allow some types of extensions without planning consent. However, permitted development rights are often removed for listed buildings and those in designated areas like National Parks.