Planning permission for extra flats on a block roof

Upward extension flats planning permission is usually obtainable. Whether the scheme is deliverable is a different question, and it is settled by the title to the airspace, the notices you owe the leaseholders and the levy you will pay, none of which the planning route resolves.

Start with the route. Class AA of Part 20 of Schedule 2 to the General Permitted Development Order 2015 allows up to two additional storeys of new dwellings above the topmost residential storey of a purpose-built detached block of flats, on prior approval. Where the right is available it is faster and the matters the authority can consider are limited. Where it is not, a full application is the only way, and it is sometimes the better way even when the right exists.

When the prior approval route works

The right only reaches buildings that meet every limitation. The ones that rule most blocks out are the construction date window of 1 July 1948 to 5 March 2018, the requirement that the block be purpose-built, detached and in residential use, a minimum of three storeys above ground for two additional storeys, a 30 m cap on the resulting height, limits on the floor to ceiling height of the new storeys, and exclusion on designated land including conservation areas, National Landscapes, National Parks, World Heritage Sites, sites of special scientific interest, and listed buildings with their curtilage.

The conditions and limitations have been amended more than once, so read the current text of Part 20 rather than any summary of it. The detail of each limitation and the matters the authority may consider are set out in the guide to Part 20 upward extension of blocks of flats.

Where any limitation is breached, the right falls away in full. There is no partial reliance, and a scheme that exceeds 30 m by 400 mm needs a planning application like any other.

Where a full application is the better route

Four situations where applicants with a valid Class AA right choose to apply anyway.

The first is design. The prior approval matters include external appearance, but the authority cannot refuse on the full range of design and policy grounds, which sounds like an advantage until a scheme has to be sold to a lender and a managing agent. A permission granted on a full application with the authority's design input behind it is easier to finance and easier to defend to leaseholders.

The second is more than two storeys, or a block that is attached, or a resulting height above 30 m. Those schemes have no choice.

The third is where affordable housing is unavoidable anyway. Prior approval under Class AA does not attract an affordable housing requirement, but where the local plan threshold would be crossed and the authority has an off-site or financial route, some developers take the full application and negotiate the obligation in exchange for a larger scheme.

The fourth is certainty. A prior approval refusal on a matter such as natural light or amenity leaves little to appeal with, because the scheme has to fit within fixed limitations. A refused full application can be revised, reduced and resubmitted or appealed on planning merits.

The airspace title question

This is the issue that stops more schemes than planning does, and the answer depends on documents rather than on design.

The freeholder owns the airspace above the top floor unless a lease or transfer says otherwise. Check whether the top floor leases include the roof, the roof void or any part of the airspace, whether any lease grants rights over the roof such as access or a terrace, and whether the leases contain covenants for quiet enjoyment or against building works that would be breached.

Then check who owns the freehold now. Where leaseholders have acquired it through collective enfranchisement, or where a right to manage company is in place, the negotiation is with them and not with an investor. That changes the commercial position entirely.

Where the airspace is to be sold or leased to a developer, the disposal may trigger the right of first refusal under Part I of the Landlord and Tenant Act 1987, which requires the landlord to offer the interest to the qualifying tenants before disposing of it elsewhere. A disposal made without the required notice can be challenged, and the consequences reach the developer who bought it. Take specialist advice on whether a particular transaction is a relevant disposal, because the answer turns on the structure. The commercial evidence a lender and a freeholder will both want is set out in the guide to airspace development above flats.

Structure, services and the existing building

The building was designed for the load it carries. Two more storeys change the load path, the foundation demand, the lift and stair capacity, the water pressure at the top of the riser and the electrical supply capacity, and every one of those is a cost item rather than a planning item.

Establish the construction type before anything else. Large panel system construction, in particular, needs investigation rather than assumption, and the approach to that evidence is set out in the guide to roof extensions and structural capacity evidence.

The services question is the one that surprises people. Adding eight flats above an existing riser often means a new riser, which means taking space from existing flats or running services externally, and both options are harder to sell to leaseholders than the roof extension itself.

Daylight, amenity and the people who will object

Every leaseholder in the block has to be consulted on a Class AA application, which means the objections arrive from inside the building.

The top floor flats lose most. They lose sky view, they gain a ceiling above them, and they live through the construction. A Daylight and Sunlight Assessment carried out to the recognised Building Research Establishment methodology, modelling existing and proposed conditions room by room, is the document that answers the daylight part. Commission it from the massing study, because a set-back top storey often turns a failing result into a passing one and that decision has to be taken early.

The construction part is answered by the construction management report, and credibility matters more than ambition there. Residents who are told there will be no disruption stop believing anything else in the submission.

Programme, fees and determination

Whether work may begin where the authority fails to determine a Part 20 application within the period depends on the precise wording of the relevant paragraph, so check the current text and take advice rather than assuming a deemed consent.

Fees are set by the national fee regulations and are indexed, so check the current schedule rather than a figure from a previous scheme. And the Community Infrastructure Levy applies to development permitted by a general consent as well as to development with planning permission: where the authority has a charging schedule, a notice of chargeable development has to be submitted before work begins, and failing to serve it loses any exemption or instalment entitlement. That is the most expensive administrative mistake available on an airspace scheme.

Set the case out in a Planning Statement addressing each prior approval matter in turn, with the design rationale in a Design and Access Statement where a full application is being made.

This is general guidance, not legal advice, and the title and leasehold issues described here need specialist legal advice on the specific documents. Permitted development rights, fees and levy rules change, so check the current position with your local planning authority or a qualified professional before relying on it.

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