Class AA Permitted Development: Adding Extra Storeys to Your Detached House
If you need more space but don’t want the time, cost, and uncertainty of a full planning application, Class AA permitted development rights may offer a solution. In certain circumstances, homeowners can add up to two additional storeys to a detached house without applying for full planning permission.
This guide explains how Class AA works, who qualifies, and what you need to consider before starting your project.
What Is Class AA Permitted Development?
Class AA is part of the UK’s permitted development (PD) framework. It allows owners of detached single-family houses to extend their home vertically by adding one or two extra storeys, provided the proposal meets strict criteria and receives prior approval from the local planning authority.
Although it removes the need for full planning permission, it is not automatic. The design must still be assessed and approved before work begins.
If you’ve been searching for answers to questions like “Can I add two storeys without planning permission?” or “How do I extend a detached house upwards under permitted development?”, Class AA is likely the regulation you’ve come across.
Does Your Property Qualify?
Class AA applies only to detached houses. It does not apply to semi-detached properties, terraced houses, flats, or maisonettes. The property must also be a single dwellinghouse rather than subdivided units.
Location is equally important. Class AA rights do not apply if your home is in a designated area such as a Conservation Area, National Park, Area of Outstanding Natural Beauty, or World Heritage Site. In those locations, full planning permission is normally required.
How Much Can You Build?
Under Class AA, you can add up to two additional storeys on top of your existing detached house. This can dramatically increase your living space, making it possible to create additional bedrooms, bathrooms, home offices, or even a new master suite.
However, there are height and size limits. The overall height of the extended house must not exceed prescribed limits set out in legislation, and the extension must be proportionate to the original building. Measurements are typically taken from the “original house” as it stood on 1 July 1948 (or when first built, if later), not from subsequent extensions.
Rear projections are also controlled, and the design must not create excessive bulk or dominate neighbouring properties.
What’s allowed:
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Add one extra storey to a single-storey home.
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Add up to two extra storeys to a home that already has two or more storeys.
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Any necessary engineering work to safely support the new storey is included.
What’s not allowed:
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Homes built before 1 July 1948 or after 28 October 2018.
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Homes located on protected land, including sites of special scientific interest.
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Properties that have already been extended upwards previously.
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Extensions that would make the roof higher than 18 metres, or increase the height too much compared to neighboring homes (especially for semi-detached or terrace houses).
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New storeys with floor-to-ceiling heights over 3 metres or taller than the existing floors.
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Extensions on parts of the house other than the main building.
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Any development that requires visible external support structures or major engineering work beyond strengthening existing walls/foundations.
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Homes that only have planning permission due to certain change-of-use classes.
Design and Neighbour Considerations
Even though this is permitted development, the impact on neighbours is still carefully assessed. The extension must not overhang side boundaries and must avoid unacceptable overlooking or loss of privacy. Daylight and sunlight to neighbouring properties are important considerations.
Fire safety is particularly significant when adding extra storeys. The scheme must meet modern building regulations standards, including structural integrity, means of escape, and insulation performance.
In short, while Class AA can simplify the planning process, it does not remove the need for a well-designed and professionally considered scheme.
What Is Prior Approval?
Before any work begins, you must submit a prior approval application to your local planning authority. This is a formal process where the council reviews specific aspects of your proposal.
They will consider the impact on transport and highways, potential noise issues, flood risk where relevant, and the overall design and external appearance of the development.
The local authority has eight weeks to issue a decision. Only once prior approval is granted (or deemed granted) can construction legally begin.
Why Homeowners Choose Class AA
For many homeowners, extending upwards makes more sense than extending outward. It preserves garden space, maximises the existing footprint, and can significantly increase property value.
Class AA offers a more streamlined route than full planning permission, which can reduce uncertainty and, in some cases, speed up the process.
In Simple Terms
Class AA permitted development allows owners of detached houses to add up to two extra floors without submitting a full planning application. The property must not be in a protected area, strict height and design limits must be met, and prior approval from the local authority is required.
If you are considering adding a second or third storey to your detached home, understanding how Class AA works could save time and help you plan your project with confidence.
