Part 20 airspace comparison table

Part 20 of the GPDO provides six different routes for creating new homes by adding storeys, or by demolishing and replacing a qualifying building. The starting point is the building’s form and lawful use. This table helps identify the class to investigate, but a matching row is not itself permission to start work.

Compare the six Part 20 classes

Read the relevant class page before relying on a row. This summary does not include every limitation or condition, including previous rooftop additions, elevations, roof space, external works, access and site-specific restrictions.

Choosing the correct use category

Classes AA and AB concern specified commercial or mixed uses: former A1 shops, A2 financial and professional services, A3 restaurants and cafés, B1(a) offices, betting offices, payday loan shops and launderettes, including defined mixes and C3 homes. The GPDO refers to the 1987 Use Classes Order as in force on 5th March 2018. A current Class E label alone does not establish eligibility. B1(b) research and development and B1(c) light industrial are relevant to the demolition route in Class ZA, but are not automatically eligible under AA or AB.

Classes AC and AD require an existing single C3 dwellinghouse, even though their historic use provisions can look back to specified former commercial uses. A commercial terrace does not qualify under Class AC merely because it is terraced. A house in multiple occupation may have a different lawful use; check the precise test rather than treating every property with accommodation as a C3 house.

Conditions that apply before work starts

• Confirm the building’s lawful use, form, age, number of storeys and permitted development history, including any prior upward addition
• Check location exclusions: article 2(3) land, a site of special scientific interest, listed buildings and their curtilages, scheduled monuments and their curtilages, safety hazard and military explosives areas, and the aerodrome restriction
• Check any Article 4 direction or planning condition restricting the specific right; the age of a Part 20 right does not prevent its withdrawal
• Apply to the local planning authority for the prior approval required by the chosen class and wait for the written outcome before commencing; the eight-week decision period does not create deemed consent to build
• Meet the applicable matters for prior approval, including external appearance, amenity, natural light, transport, flooding, contamination, air traffic and defence impacts; commercial buildings have further noise and business impact matters, and qualifying taller buildings under A or AA have fire safety considerations
• Ensure the new homes meet the minimum 37m² gross internal area and national described space standard requirements in Article 3(9A), and address building regulations and any other consents

New dwellinghouses created under these rights must be used as Class C3 dwellinghouses. The class-specific rules also control construction timing, construction management where applicable and completion notification. See Paragraph B: prior approval procedure and Paragraph C: interpretation.

Part 1 is a different route

Part 1 Class AA concerns adding living space to an existing house, subject to its own tests. The Part 20 routes in this table create new self-contained C3 homes. Work that extends an existing house is not automatically within Part 20.

Primary sources: GPDO Schedule 2 Part 20, GPDO Article 3, GPDO Article 4 and government planning guidance on upward extensions.

Page updated 24th September 2026

Explore GPDO Part 20

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