Building Regulations and Planning Permissions

Will I need Planning Permission? A guide to Permitted Developments

Knowing whether planning permission is required is a key element in the early stages of planning a home renovation project. Whether you are planning to add a conservatory, orangery, garden room or glass box extension, there are a number of factors that determine whether planning permission is required before any building work commences.

Permitted development rights

Most homes will have Permitted Development Rights (PDR), which allow the homeowner to extend a terraced, semi-detached or detached property without needing to seek additional planning permission, as long as the dimensions of the extension fall within specific parameters.

Although most properties will have PDR, some circumstances may have resulted in its removal for specific houses, so it is worth confirming the home’s status before commencing any works. Homeowners can check the PDR status on their home by contacting their local planning authority.

In order to qualify as a permitted development, a home renovation project must adhere to all relevant criteria, with specific parameters depending on the type of extension chosen. It is worth noting that the following planning advice is applicable only to houses and does not include flats, maisonettes, converted houses, commercial buildings or other structures.

Cambridge Road Sliding glass doors

Criteria for a permitted development: rear extensions

One of the most common ways to extend a home, the criteria for building a rear extension without requiring additional planning permission is relatively straightforward. Restrictions on height and maximum floorspace apply to both single and double storey extensions and can be summarised under the following points:

  • The maximum footprint of the extension or garden room must be less than half of the land around the house as it stood when it was first built, or in 1948, whichever is the earliest date. This means that if a previous owner has already built an extension, you can only extend out further if this still falls within the permitted 50% floorspace of the original building.
  • The extension cannot be higher than the highest part of the existing roof, nor can the eaves of the extended section be higher than the existing eaves.
  • Extensions higher than 1 storey must not extend more than 3m beyond the original rear wall of the property, or be within 7m of the rear boundary line.
  • If the extension comes within 2m of the opposite rear property boundary, the height at the eaves cannot exceed 3m.
  • The extended roof pitch must match that of the existing roof as closely as possible.
  • Upper floor windows on the side elevation of the extension must be obscured glazed and non-opening.

Side extensions

  • Single storey side extensions cannot extend beyond the original rear wall by more than 4m for detached houses, and 3m for terraced and semi-detached homes.
  • The extension must not be wider than half the width of the original house.
  • Side extensions must adhere to a maximum height of 4m, or 3m if within 2m of a property boundary.
  • You cannot build on more than 50% of your private garden space. It is important to factor in any existing sheds or outbuildings when calculating the available space that the side extension can occupy.
  • All side extensions higher than one storey will require planning permission by default.

Mondrian steel glazed extension

Loft conversions and rooflights

Converting a disused loft space is a great way to add extra living space without the need to extend the home. Oftentimes this involves adding rooflights to create a light filled room. The good news is that this kind of development doesn’t carry any planning permission implications, as long as the rooflights are a reasonable size and can be supported by the original roof structure.

Additional requirements to be aware of include:

  • Windows are not permitted in any wall or roof slope that makes up part of the side elevation of the property.
  • For loft or roof extensions, the build cannot add more than 40 cubic metres of space to a terraced house or 50 cubic metres to a detached or semi-detached house.
  • Windows must be non-opening. For a PDR compliant glazing solution, venting and sliding rooflights such as the MARS or ARES are permitted.
  • The roof pitch of the main part of the loft extension must be the same as the roof pitch of the existing house.

loft conversion with rooflights

Garden Rooms & Outbuildings

Outbuildings, including garden rooms, garages and enclosed swimming pools, are usually permitted depending on size, location and intended purpose – i.e. as long as you are not creating self-contained accommodation, which carries a permission application process. In order to meet the criteria, the build must follow a few additional guidelines:

  • Garden rooms must not be built on land forward of the front-facing elevation of the main property.
  • The building must have a maximum eaves height of 2.5m and an overall height of 4m. If located within 2.5m of another outbuilding, or within 2m of the main dwelling, the maximum height lowers to 2.5m.
  • No more than half of the private garden space surrounding the original house must be covered by outbuildings.
  • Buildings to the side of a property will automatically require planning permission.

minimal windows glass garden room

Other extension types

Wraparound extensions

When planning a wraparound extension project that combines a side and rear extension, the permitted development restrictions are evaluated individually. This means it is unlikely that the extension will fall under PDR guidelines and will likely require planning permission.


Basement renovations are usually permitted if the work is converting an existing cellar or basement, as long as it is not going to be used for self-contained accommodation and doesn’t alter the exterior appearance of the building.

Replacement glazing

For simple renovations that just involve replacing existing windows and doors, planning permission is rarely required.

double height glass infill extension

Green Belt homes - Article 2(3) Designated Land

Planning regulations are much tighter for areas under the Designated Land classification. This includes areas of outstanding natural beauty, conservation areas, National Parks and World Heritage Sites.

In these areas, rear extensions with more than one storey will automatically require planning permission, while all side extensions, regardless of height, will require planning permission by default. Any outbuildings such as garden rooms will also require permission.

Some homes within these areas will still follow the usual Permitted Development Rights, so it is worth checking this before applying for permission. Owners of homes in these areas shouldn’t be put off from considering an extension, however, as even projects that do require planning permission will usually be approved without any complications, as long as the house hasn’t already been overextended.

Stone haven minimal sliding glass doors

Getting advice on your project

If planning permission is needed, it is useful to get pre-application advice from your local authority to highlight any potential issues with your application.  The Royal Town Planning Institute recommends discussing any plans with neighbours and to check the previous planning applications made on the property, as this could give you some useful insight into what may be rejected and the reasons why.

Elements of frameless glass and frameless assemblies are usually favoured due to the transparent nature of glass, as there is minimal overshadowing to neighbouring properties and using glass as a building material maintains the original design of the building.

Any project designed by an architect will have a much greater chance of gaining planning permission, if it is needed, while also carrying the advantage of having access to expert advice as to what designs would be more sympathetic to the surrounding buildings.

Get in touch with us today for expert advice on your renovation project.