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What is the difference between a roof window and a dormer window?

A roof window (or skylight) is fitted flush within the slope of a roof, while a dormer projects outward, creating additional headroom and floor space.  

Both can be installed under permitted development but must meet specific size and position limits to qualify.  

Also consider building regulations for a new dormer, find out more on Planning Portal  

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Common Questions

Do I need planning permission to brick up an existing window?

Bricking up or infilling an existing window is classified as permitted development, meaning an application for planning permission is not required to complete the works. You will need to ensure that any materials used are of a similar appearance to the existing exterior of the house.

If you live in a listed building, then you will require planning permission and listed building consent for the change. In this instance it is best practice to talk to your local planning authority first.

What are Approved Documents and where can I find them?

Approved Documents are official guides that explain how to comply with the building regulations. Published by the government, each document provides practical guidance on meeting the requirements of a specific ‘Part’ of the regulations. They cover a wide range of building work, including plumbing, electrical installations, extensions and ventilation.

The latest versions of the Approved Documents, which support the technical ‘Parts’ of the building regulations, along with Regulation 7, are available on Planning Portal.

Browse the Approved Documents.

Do I need planning permission to add a first-floor extension onto an existing ground floor extension?

Adding a storey on top of an extension will always require an application for planning permission.

If you want to add a storey on top of your house under permitted development rights, it must be on the principal part of the house.

If you want to add an additional storey on top of your house, it can be permitted development. It is only permitted development if it follows certain rules:

The current house

  • Is not a building containing one or more flats, or a flat contained within such a building
  • Was constructed between 1 July 1948 and 28 October 2018
  • Has not already had additional storeys added to it
  • Is not on Article 2(3) land or a site of special scientific interest
  • Was not changed to be used as a house (from a previous non-residential use) under permitted development rights.

How many storeys can you add?

  • If the house is one storey then one storey can be added
  • If the house is two or more storeys then two storeys can be added

Where can the storeys be added?

  • The additional storeys must be added to the principal part of the house. The principal part of the house is the main part of the house excluding any front, side or rear extension of a lower height (regardless of these being part of the original house or subsequent additions).
  • Engineering operations must only include works within the existing curtilage of the house to strengthen existing walls and foundations

How high can it be?

  • The house cannot exceed 18 metres in total height
  • Each storey cannot add more than 3.5 metres to the total height
  • If the house is not detached the total height cannot be more than 3.5 metres higher than the next highest building that the house is attached to, adjoins, or is in the same row as.
  • The additional storeys must have an internal floor-to-ceiling height of no more than 3 metres, and no greater than the internal height of any existing storey within the principal part of the house.

What materials can be used?

The materials used must be of a similar appearance to those used in the construction of the exterior of the current house

Where can windows be placed?

Windows must not be placed in any wall or roof slope forming a side elevation of the house.

Following completion of development:

  • The house must remain in use as a domestic residential property
  • No visible support structures must remain on or attached to the exterior of the house
  • The roof pitch of the principal part of the house must be the same as it was prior to the development.

 If any of the limits set out above are exceeded then an application for planning permission will be required. If you are unsure, you should contact your local planning authority.

Find contact details for your local planning authority.

What are the height restrictions for fences, gates and garden walls?

You can usually put up new fences, gates or garden walls without planning permission, as long as you stay within permitted height limits. If the structure is adjacent to a highway (including footpaths), it must not exceed one metre in height. For all other boundaries, the maximum permitted height is two metres. Anything taller than these limits will require planning permission.  

Read more about fences, gates and garden walls.

Is building regulations approval needed for a garage conversion?

The conversion of a garage, or part of a garage, into habitable space, will normally require approval under the building regulations.

As part of the garage conversion, it is likely that the original garage door will be in-filled with a new wall and possibly a window or door, and a new foundation may be needed for the new wall. 

As well as the foundation, you also need to consider:

  • Floor
  • Walls  
  • Ventilation

Read more about the building regulations for garage conversions.

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