Adding an extra floor to your home can dramatically increase both living space and property value without sacrificing garden space.
Since 2020, Class AA of the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO) has allowed certain houses in England to add one or two additional storeys using Permitted Development Rights, subject to Prior Approval from the local planning authority.
While this avoids a full planning application, it is not automatic. Strict eligibility criteria, design rules and Building Regulations requirements still apply.
This guide explains who can use Class AA, the limitations involved and the steps required to secure approval.
Please note: This guide applies to England only. Permitted Development legislation changes periodically, so the current rules should always be checked before proceeding.
What Is Class AA?
Class AA is a form of Permitted Development that allows certain existing houses to be extended upwards by adding additional storeys.
Unlike standard Permitted Development, Class AA requires Prior Approval from the local planning authority before work can begin.
Prior Approval is a simpler process than a full planning application, but councils still assess several planning matters before granting consent.
Is Your House Eligible?
Class AA only applies to certain houses. Generally, the existing property must:
- Be a single dwellinghouse (Use Class C3).
- Not be a flat or maisonette.
- Have been built between 1 July 1948 and 28 October 2018.
- Not already have had additional storeys added above the original house.
- Not have been created through certain Permitted Development change‑of‑use rights.
- Not be located within land excluded from Class AA, including conservation areas, National Parks, Areas of Outstanding Natural Beauty, the Broads, World Heritage Sites or Sites of Special Scientific Interest.
If you’re unsure whether your property qualifies, our guide Permitted Development Rights Explained: What Can You Build Without Planning Permission? explains how Permitted Development works more generally.
How Many Storeys Can You Add?
The number of additional storeys depends on the existing building. Typically:
- A bungalow may add one additional storey.
- A house with two or more existing storeys may add up to two additional storeys.
Strict height limitations apply. The completed building must:
- Not exceed 18 metres in overall height.
- Not increase by more than 3.5 metres per additional storey.
- For terraced and semi‑detached houses, not exceed the height of the highest adjoining building by more than 3.5 metres.
Internal floor‑to‑ceiling heights are also controlled.
Design Restrictions
Additional Storeys Must Sit on the Principal Part of the House
The extension must normally be constructed above the principal part of the existing house. Additional storeys cannot usually be built above:
- Lower rear extensions.
- Side extensions.
- Front projections.
Roof Pitch
The finished roof pitch should match the existing principal roof wherever applicable.
Materials
External materials should be similar in appearance to those used on the existing house, including brickwork, roof coverings and external finishes.
Side Windows
Windows within side elevations are generally not permitted under Class AA. Alternative daylight strategies, such as rooflights, may therefore be required.
What Does Prior Approval Cover?
These matters are typically assessed:
- Impact on neighbouring amenity.
- Privacy and overlooking.
- Loss of daylight.
- External appearance.
- Air traffic and defence safeguarding where relevant.
- Protected London views where applicable.
Neighbouring owners and occupiers are normally notified and given an opportunity to comment. Most Prior Approval applications are determined within approximately eight weeks.
Additional Conditions
Once Prior Approval has been granted, further requirements include:
- Submission of a Construction Management Plan before work begins.
- Completion of the development within three years.
- Written notification to the local planning authority once construction has finished.
Failure to comply may invalidate the approval.
Building Regulations Still Apply
Class AA only deals with planning legislation. Building Regulations approval is still required before construction begins.
Structural Design
Adding an additional floor significantly increases the structural loading on the existing building. Structural calculations will normally be required for foundations, existing walls, steel beams, floor construction and lateral stability.
Fire Safety
Additional storeys often trigger more demanding fire safety requirements, including protected escape routes, fire doors, smoke detection and fire‑resistant construction.
Thermal Performance
The new construction must comply with Part L of the Building Regulations, including insulation and airtightness requirements.
Sound Insulation
Floor construction must also satisfy Part E where applicable.
Stairs
New staircases must comply with Part K, covering headroom, rise and going, handrails and guarding.
Our Building Regulations Drawings service provides the detailed technical drawings required for Building Control approval once Prior Approval has been obtained.
What Class AA Does Not Allow
- Convert houses into flats.
- Add storeys to flats or maisonettes.
- Extend buildings created through certain Permitted Development change‑of‑use rights.
- Build within excluded protected areas.
- Add further storeys above houses that have already been extended upwards under Class AA.
Common Mistakes
Many proposals fail because homeowners:
- Assume Prior Approval is automatic.
- Exceed height limitations by small amounts.
- Introduce prohibited side windows.
- Overlook Article 4 Directions or planning conditions.
- Begin work before Prior Approval has been granted.
Early feasibility work can identify these issues before design costs are incurred.
Typical Project Process
- Confirming eligibility.
- Measured building survey.
- Feasibility design.
- Preparation of the Prior Approval application.
- Structural design.
- Building Regulations drawings.
- Construction Management Plan.
- Construction.
- Completion notification.
Is Class AA Right for Your Home?
Class AA offers a valuable opportunity for many homeowners to create substantial additional living space without making a full planning application. Professional advice at the feasibility stage can often save significant time and expense.
Thinking About Adding an Extra Storey?
At Draw & Plan, we assess whether your property qualifies for Class AA Permitted Development before any drawings are prepared. Our Planning Drawings service includes feasibility assessments, Prior Approval applications and coordination with local planning authorities to maximise your chances of success.
Once Prior Approval has been granted, our Building Regulations Drawings provide the detailed technical information required for Building Control approval, working alongside structural engineers to coordinate the construction package.
If you’re still unsure whether your proposal qualifies under Permitted Development, our guide What Is the “Original House” Under Permitted Development? explains one of the key concepts that affects eligibility.
Ready to discuss your project? Contact us today for a free, no‑obligation quotation.
Disclaimer: This article is for general informational purposes only and does not constitute legal or professional advice. Class AA Permitted Development Rights apply only in England and are subject to detailed eligibility criteria, conditions and limitations. Always seek advice from a suitably qualified planning professional or your local planning authority before commencing development.