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Paragraph B: Part 20 prior approval procedure
Paragraph B sets the application and decision procedure for the rooftop homes and replacement buildings permitted by Part 20 of the General Permitted Development Order. Every proposal still has to meet the relevant class’s limits and conditions. A complete application and a favourable decision on the relevant prior approval matters are both needed before work begins.
The application documents differ for Class ZA demolition and replacement and for Classes A to AD. The distinction matters when assembling drawings and supporting statements.
England only. Paragraph B is in Schedule 2, Part 20 of the 2015 GPDO as amended.
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What to submit for Classes A to AD
Paragraph B(2) requires the following with the applicable fee. The authority can ask for more information reasonably needed to determine the application under B(14).
- A written description of the development, including the new homes and other operations permitted by the relevant class
- A site plan drawn to an identified scale, showing north and the proposed development
- Scaled, north-pointing floor plans showing the total floor space in square metres of each proposed home, dimensions and proposed use of every room, and the position and dimensions of windows, doors and walls, together with existing and proposed elevations
- A written statement of the number of new homes added to the existing building
- A list of every flat and other premises address within the existing building
- The developer’s contact address and an email address if electronic communications are acceptable
- A site-specific flood risk assessment where B(6) requires consultation with the Environment Agency
- For a Class A or AA proposal meeting the fire risk condition in Paragraph C(3), a statement describing the fire safety design principles, concepts and standards applied to the development
- For a Class A or AA application concerning the external wall safety matter in A.2(1)(i) or AA.2(1)(k), a report from a chartered engineer or other competent professional confirming that the existing external wall construction complies with paragraph B4(1) of Schedule 1 to the Building Regulations 2010
Only Classes A and AA contain the fire safety impacts prior approval matters, in A.2(1)(j) and AA.2(1)(l). Classes ZA, AB, AC and AD have no equivalent fire safety impacts prior approval matter under Part 20. The external wall matter applies where the existing Class A or AA building is at least 18 metres high. The separate fire risk condition in Paragraph C(3) uses the building after development and an 18 metre or seven storey test. They are different checks. Under B(9A), the authority must refuse approval for the A/AA external wall matter if the required professional report is missing.
Class ZA has its own document list
Paragraphs B(1A) to B(1C) replace B(2) for Class ZA. Submit a description identifying the building to be demolished, its replacement and any ZA(3) operations; a scaled north-pointing site plan; and scaled drawings of both buildings’ external dimensions, elevations and northward positioning. The drawings must, as far as practicable, show the proposed homes’ windows, doors and walls and the dimensions and use of all habitable and other rooms under B(1B).
Also provide a statement of the number of existing homes in the demolition building and proposed new homes, a heritage and archaeology statement, contact details, any triggered site-specific flood risk assessment, and the fee. Paragraph B(1C) expressly disapplies the A to AD list in B(2) to Class ZA. Check the full Class ZA eligibility and conditions separately.
Building Safety Regulator amendment from 21st October 2026
SI 2026/1056, article 9, replaces the words “the Health and Safety Executive” with “the Building Safety Regulator” in paragraph B(2)(h)(ii) and B(6A), from 21st October 2026. The consultation and fire-safety references below describe the pre-amendment wording; from that date read the named body as the Building Safety Regulator. This technical change does not widen the Classes or fire-safety triggers.
Eligibility and consultations
The council may refuse the application under B(3) where the proposal fails a Part 20 condition, limit or restriction, or where the evidence is insufficient to establish compliance. Such a refusal is treated as a refusal of approval for appeal purposes under B(4), without going through the ordinary consultations and notices listed there.
| Matter | Paragraph B requirement |
|---|---|
| Highways | B(5): where traffic is likely to increase materially or change character materially, consult the relevant trunk road, local highway or railway bodies according to the affected route |
| Flooding | B(6): consult the Environment Agency for Flood Zones 2 and 3, and for Zone 1 land with critical drainage problems notified to the authority by the Agency |
| Fire safety | B(6A): for a Class A or AA application where fire safety impacts are a prior approval matter under A.2(1)(j) or AA.2(1)(l), consult the Health and Safety Executive |
| Air traffic and defence | B(7) and (8): consult relevant operators and, where appropriate, the Civil Aviation Authority and Defence Secretary; do not approve contrary to their advice on a safeguarded map |
| Natural light | B(9): refuse approval unless adequate natural light is provided in every habitable room of the proposed homes |
| Protected views | B(10): consult Historic England, the Mayor of London and relevant authorities identified in the protected vistas directions |
| Heritage and archaeology | B(10A): consult relevant expert bodies so far as reasonably practicable, where this prior approval matter applies |
Under B(11), the authority gives those statutory consultees at least 21 days to respond. Public holidays are disregarded when calculating that period.
Publicity, evidence and decision
Under B(12), the council must display a site notice on or near the land for at least 21 days. It must also serve notice on adjoining owners or occupiers and, except for Class ZA, on owners and occupiers of flats and other premises in the existing building. The site notice describes the proposal, gives its address and sets the representations deadline. Public holidays are disregarded when counting its 21 days under B(13).
When deciding, the council considers consultation responses and representations, and has regard to the National Planning Policy Framework so far as it is relevant to the prior approval subject matter. B(15) also requires an assessment of contamination risk and refusal if the site would become contaminated land within Part 2A of the Environmental Protection Act 1990 after proposed mitigation.
The authority may grant approval unconditionally or attach conditions reasonably related to its subject matter. Under B(16), work must not begin until the applicant receives a written notice giving prior approval. Paragraph B contains no deemed approval through the lapse of 56 days. Development must then follow the approved details under B(17). Other class-specific requirements, including construction deadlines and notification on completion, remain applicable.
Fire safety and minimum size are separate requirements
Paragraph C(3) defines the fire risk condition relevant to fire safety impacts prior approval under Classes A and AA. It concerns a building that, after development, will contain at least two dwellinghouses and meet the height test in article 9A(3) and (7) of the Development Management Procedure Order: 18 metres or more, or seven or more storeys. Only when Class A or AA fire safety impacts are in scope do B(2)(h)(ii) and B(6A) require the design statement and HSE consultation. That trigger is separate from the Class A/AA external wall report for an existing building at least 18 metres high. Paragraph B does not create a fire safety impacts prior approval matter for Classes ZA, AB, AC or AD.
Separately, GPDO article 3(9A) prevents permission for a new dwellinghouse under Part 20 unless it has at least 37 square metres of gross internal area and complies with the nationally described space standard. These requirements do not disappear because the prior approval matters are satisfied.
Primary legislation
Explore GPDO Part 20
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Page updated: 1st October 2026