Your feedback matters
Want to learn everything about Webflow? Download our free eBook today.
.svg){kind=small}
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
Widening or creating a new external doorway will likely fall under permitted development rights, meaning an application for planning permission is not required provided you meet limits and conditions set out in legislation. If the change is on the side or rear of the building it is more likely to comply with planning regulations.
If you live in a listed building, you will have to apply for listed building consent for any significant works, whether internal or external.
New external doorways which create a new or widened opening must comply with building regulations as they may impact the structure of a building.
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.
Merging two flats into one, commonly known as amalgamation is likely to require planning permission as it will impact the local planning authorities housing supply. The council’s views on this will vary from council to council. It is recommended that you contact your local planning authority to understand their position.
If you do not need to apply for planning permission then you can apply for a lawful development certificate to prove that the change is lawful.
Building regulations will be required if there are physical works taking place as part of the amalgamation, this may include removing walls or changing electrics. Visit the relevant common projects on our site for more information.
You will often not require planning permission to fit a log burner. If you are adding a new external flue or chimney then different rules will apply.
If you live in a listed building you will require listed building consent.
The installation of a log burner must comply with building regulations. It is recommended that you use a HETAS-registered installer who can certify the work. Visit the HETAS website to search for an installer.
Read more information around fitting an external flue or chimney in our common projects section.
In many circumstances, rules known as ‘permitted development’ rights allow you to extend a house without needing to apply for planning permission, providing specific limitations and conditions are met. If you want to exceed these limits and conditions, then it is likely that an application for householder planning permission will be required.
The limits and conditions for building an extension under permitted development rules are covered in our guidance on the Planning Portal, and there are other points to take into consideration.
Visit Planning Portal to find out more.
