Permitted development for house extensions

When extending your home, it is often assumed that you will need planning consent; however, in some instances, house 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.

Architecture for London is an RIBA Chartered Practice with several permitted development house extensions in London. View our portfolio of recent work, or contact us on 020 3637 4236 to discuss your project.

Building a house extension without planning consent

Rather than relying on the local authority to grant planning permission to extend your home, you may be entitled to extend without planning approval at all. 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 before building. This can be done by applying for a ‘lawful development certificate’ (LDC).

De Beauvoir extension by Architecture for London

Permitted development: 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 an 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 has 8 weeks to determine the application.

Why not just apply for planning for house extensions?

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 that 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.

Queen’s Park House by Architecture for London

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.

Contact us now on 020 3637 4236 for a free 30-minute telephone consultation to discuss your project.

The local authority may not wish for you to extend the back of 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 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.

Loft conversion PD volume calculation by Architecture for London

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 has several 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. This class 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 roof lights.

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

Class E

Buildings and structures 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.

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

Permitted development for house extensions: restrictions

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.

Dartmouth Park extension: dining room detail

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
• 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.

Dartmouth Park extension: detail of garden doors and barbecue

How big can I build my house extension under permitted development?

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

For a typical terrace house in London that is 5m wide, this would be a rear extension of 15 sqm, 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 an 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.

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 who did not object to this development. Perhaps the more isolated properties in London would have a better 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 that 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 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. 

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

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.

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

Permitted development FAQ