Airspace development above flats: the evidence pack

Airspace development evidence for a block of flats has to satisfy four different readers at once: the planning officer on design and amenity, the building safety consultee on fire, the highway authority on construction logistics, and the leaseholders whose roof you are proposing to build on. Schemes fail because one of those four is treated as a later problem. The fire and structural evidence in particular has to be assembled together, because the structural solution chosen for the new storeys changes the fire strategy and the escape arrangements for people already living in the building.

Assemble the pack before you finalise the drawings. Airspace schemes that go the other way round get redesigned.

What the application must demonstrate

Whether the scheme comes forward as a full application or as prior approval under the upward extension classes, the authority has to be satisfied on a defined list. Design and external appearance. Amenity of the existing building and of neighbours, including daylight, outlook and privacy. Structural capability. Fire safety where the building falls within the relevant category. Construction impacts on an occupied building and on the street.

Two features of airspace work make this harder than an ordinary application.

The building is occupied throughout, so every survey, every construction method and every temporary arrangement has a resident consequence that the officer will be told about during consultation. And the existing building was designed to an earlier set of standards, so the scheme has to demonstrate that adding to it does not make the existing position worse.

Write the covering statement around those two facts rather than around the merits of the new flats.

Structural and fire evidence together

The structural appraisal establishes what the existing building can carry and by what route. That answer determines the structural material for the new storeys, and the material determines the fire engineering.

A light gauge steel or engineered timber solution keeps loads down and may be the only way the building works structurally. Each brings its own fire questions about compartmentation, cavity barriers, surface spread and the protection of the structure itself. A scheme that presents the structural report and the Fire Statement as unconnected documents invites the consultee to ask how they were reconciled.

Where the completed building will reach 18 metres or seven storeys, it falls within the higher risk regime under the Building Safety Act 2022, which brings the regulator in as a consultee at Planning Gateway One and requires the fire statement with the application. Adding two storeys to a five storey block can cross that line, and the cost and programme consequences run well beyond the planning stage.

The Fire Safety Strategy that follows should address the whole building rather than the addition, because the existing block's means of escape, stair capacity and firefighting provision are now serving more flats than they were designed for.

Access and escape during and after works

Two separate questions, and applicants usually answer only the second.

After completion, the escape strategy has to work for the enlarged building. That means examining stair capacity, travel distances on the new floors, the single stair position in many older blocks, firefighting shaft provision, and whether a firefighting lift is now required. Where the existing stair is the constraint, the number of additional storeys may be fixed by escape rather than by structure.

During the works, escape from the existing flats has to be maintained at all times while the roof above them is opened up. Set out the phasing, the temporary protection to the existing top floor, the scaffold design and its effect on escape windows and routes, and the management arrangements when a route is temporarily altered. Residents will ask about this at consultation, and an answer prepared in advance is worth more than one improvised at a meeting.

Fire service access to the building has to be maintained too, which interacts directly with the construction logistics on the street.

Daylight effects on existing occupiers

Adding storeys to a block usually affects the neighbours across the street more than the residents below, and both need assessing.

The assessment should cover daylight and sunlight to surrounding habitable rooms, sunlight to existing gardens and amenity space, and overshadowing of any communal amenity area serving the existing block. Where the block has a podium garden or a courtyard, the addition can take it below the point where it works as usable space.

Run the Daylight and Sunlight Assessment early, because the result can remove a storey. Run an overshadowing study where amenity space is the sensitive receptor rather than windows.

Privacy deserves separate attention on an airspace scheme. New windows and balconies at a height nobody previously occupied can overlook gardens and rooms that were private, and the honest design response is usually window position and balcony orientation rather than obscure glazing after the event.

Leasehold and ownership matters

The planning application and the property position are separate, and confusing them causes the most expensive mistakes in this field.

Planning permission does not grant any right to build. The right comes from ownership of the airspace or a lease of it, and in many blocks the roof and airspace are demised or subject to rights that prevent development. Where leaseholders have acquired the freehold collectively, or hold rights of first refusal, a sale of airspace may engage those rights.

For the application itself, complete the ownership certificate correctly and serve notice on every owner whose land is included. On a block of flats that can mean a long list, and an incorrectly completed certificate is a defect in the application rather than a technicality.

Practical points to settle before submission:

• Who owns the airspace, evidenced from the title rather than assumed.
• Whether the leases reserve rights that the works would breach.
• Whether statutory rights of first refusal or enfranchisement rights are engaged.
• Who is responsible for making good damage to the existing building and its finishes.
• How the service charge and management arrangements change on completion.
• Whether insurers of the existing building have been notified.

Construction logistics on an occupied site

This is where local objection concentrates, and it is the part most capable of being answered with a document.

The logistics plan should cover the compound location, hoarding, crane position and oversail, delivery routing and hours, waste removal, protection of parking and access for existing residents, and the management of noise, dust and vibration in a building people are living in. Where a crane will oversail land outside the site, the position is covered in our note on crane oversail and its planning limits.

Two items that are easy to overlook. Asbestos in an older block is likely, and surveys have to come before any opening up, a point our note on asbestos surveys before demolition and refurbishment covers. And temporary works to the existing roof have to keep the building watertight through a winter, which is a planning matter only indirectly but a resident relations matter immediately.

A Construction Management Plan that names the responsible person and the complaints procedure does more to reduce objection than any amount of design justification.

Assembling the submission

Order the pack so that each document answers a question the previous one raised.

1. A design and access statement setting out the approach to height, appearance and amenity.
2. The structural appraisal, with what has been surveyed and what remains assumed.
3. The fire statement and, where relevant, the strategy for the whole building.
4. The daylight, sunlight and overshadowing assessment.
5. The construction management and logistics plan.
6. An escape and access statement covering the works phase and the completed building.
7. The ownership certificate and notices, with a schedule of who was served and when.
8. A residents engagement note recording what was consulted on and what changed.

Point eight is optional and it changes outcomes. Airspace schemes are decided in an atmosphere set by the existing residents, and a scheme that consulted them before submission arrives at committee in a different position from one that did not.

This is general guidance, not legal advice. Structural, fire and daylight assessment of an existing occupied building all require suitably qualified professionals, and for specialist technical reports, qualified professional input may be required. PlanScope can draft the planning documents around their findings, and a reviewer should check the technical content before submission.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.