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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.
Common Questions
It is likely that you will require planning permission to extend an existing front porch to add a toilet.
Adding a porch falls within permitted development rights meaning an application for planning permission is not required provided specified limits and conditions are met. However, to fall under permitted development rights for a porch, the total ground area must not exceed three square metres. This is unlikely to be enough room to fit toilet and the required additional components.
Read the full rules for porches under permitted development on our mini guides.
If your porch exceeds these limits, it will be classified as an extension. These can be permitted development but come with a different set of rules.
Extensions are not permitted development if they are built forward of the ‘principal elevation’ of the house. As such, you will be required to submit an application for planning permission to your local planning authority.
If you live in a listed building, you will need listed building consent for any significant changes.
For houses, replacing windows with double glazing usually doesn’t require planning permission, provided the style and appearance are similar to the original. However, if you live in a flat/maisonette, listed building, or a conservation area, planning permission or listed building consent may be required, especially if the changes affect the external appearance.
Read more about planning permission for windows and doors for houses
Read about planning permission for windows and doors for flats and maisonettes
The failure to obtain planning permission or comply with the details of a permission is commonly known as a 'planning breach'.
A planning breach usually occurs when:
- A development that requires planning permission is undertaken without the permission being granted - either because the planning application was refused or was never applied for
- A development that has been given permission subject to conditions breaks one or more of those conditions.
If the breach involves a previously rejected development (or the retrospective application fails) the council can issue an enforcement notice requiring you to put things back as they were.
There are statutory time limits for enforcement, these vary based on when the breach took place.
If the breach took place prior to 25 April 2024
- Change of use of a building, or part of a building, to use as a single dwelling house - Enforcement action can no longer be taken once the unauthorised use has continued for four years without any enforcement action being taken
- Operational development relating to building, engineering or mining - Enforcement action can no longer be taken from four years, beginning the date where the operations were substantially completed.
If the breach took place on or after 25 April 2024
- Change of use of a building, or part of a building, to use as a single dwelling house - Enforcement action can no longer be taken once the unauthorised use has continued for ten years without any enforcement action being taken
- Operational development relating to building, engineering or mining - Enforcement action can no longer be taken from ten years, beginning the date where the operations were substantially completed.
Other time limits:
There is no time limit for enforcement on breaches of planning control relating to relevant demolition.
For any other breach of planning control, ten years beginning with the date of the breach. This predominantly applies to changes of use.
Read more about breaches of planning control and lawful development certificates on Planning Portal.
If you plan to put up a small, detached building like a garden shed, garden room, garden office, annexe or summerhouse (all classed as outbuildings), building regulations generally won’t apply if the building has a floor area under 15 square metres and does not include any sleeping accommodation.
For buildings with a floor area between 15 and 30 square metres, building regulations approval is usually not needed - as long as the building does not include sleeping accommodation and either:
- it is at least one metre away from any boundary, or
- it is built mainly from non-combustible materials.
Read more about the building regulations that apply to outbuildings.
Don't forget to check the permitted development rights for outbuildings.
Creating a new basement will usually require planning permission, particularly if it affects the external appearance of the property. For example, installing a lightwell to bring natural light into the basement may be subject to stricter design rules if it is visible from the street, especially at the front of the property, compared to those at the rear or side.
Because basement construction involves significant excavation and structural work, permission is often necessary. It’s recommended that you consult your local planning authority early on to understand what is likely to be considered acceptable before submitting a planning application. Building regulations will also apply to a new or conversion of a basement.
