Reports for a two storey roof extension to a flat block

The upward extension planning reports you need for adding two storeys to a block of flats depend first on whether Class AA of Part 20 of Schedule 2 to the General Permitted Development Order 2015 is available. If it is, the evidence is shaped by the defined list of matters the authority may consider on a prior approval application. If it is not, you are making a full planning application and the evidence base is wider.

Work out the route before you commission anything, because the two paths produce different documents and a prior approval application that strays into material the authority cannot consider wastes fee and time.

Whether the prior approval route is available

Class AA permits the construction of up to two additional storeys of new dwellings immediately above the topmost residential storey of a purpose-built detached block of flats, subject to conditions and limitations. The ones that rule most buildings out:

• The existing building must have been constructed between 1 July 1948 and 5 March 2018.
• The building must have three or more storeys above ground level for two additional storeys to be permitted.
• The resulting building must not exceed 30 m in height.
• New storeys are limited in floor to ceiling height, by reference to a stated maximum and to the height of existing storeys, whichever is lower.
• The right is excluded on a long list of designated land, including conservation areas, National Parks, National Landscapes, the Broads, World Heritage Sites, sites of special scientific interest, safety hazard areas and military explosives storage areas, and on listed buildings and land within their curtilage.

Check the current text of Class AA rather than a summary, including this one, because Part 20 has been amended more than once since it was introduced. Where any limitation is breached the right falls away entirely and a full application is the only route.

A certificate of lawfulness under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that proposed works would be lawful. On a scheme of this value, with leaseholders watching, it is worth the fee.

Daylight to existing and neighbouring flats

This is the evidence that decides most upward extension schemes, and it has two separate strands.

Natural light to the new dwellings is a matter the authority considers on a prior approval application, and the test is whether all habitable rooms in the new units have adequate natural light. Rooms lit only by a rooflight over a deep plan, or by a window in a recessed slot between service cores, fail.

Amenity of the existing building and neighbouring premises, including overlooking, privacy and loss of light, is a separate matter. That means daylight and sunlight to the top floor flats of the host building, which lose sky view most, and to any neighbouring block within the affected arc. A Daylight and Sunlight Assessment carried out to the recognised Building Research Establishment methodology is the document that answers it, with the existing and proposed conditions modelled and the retained values reported room by room.

Commission it from the massing study rather than from the final drawings. A storey set back by two metres from the parapet often converts a failing assessment into a passing one, and that is a design decision rather than a reporting one.

Structural capacity of the existing building

A 1960s or 1970s block was designed for the loads it carries, not for two more storeys. The structural question is not formally a prior approval matter, but it governs whether the scheme is buildable and it governs the cost, so it is the first thing to establish.

What a Structural Survey for an upward extension needs to establish is the existing frame or wall construction and its load path, foundation type and bearing capacity, the condition of the existing structure including any concrete testing where large panel system construction is suspected, the capacity of the existing lift and stair cores and whether they can be extended, and the feasibility of transferring new loads to the existing foundations or the need for new piles through the building.

Large panel system blocks deserve particular caution. Where the original construction type is uncertain, intrusive investigation costs far less than discovering the answer on site.

Fire evidence where height increases

Height changes the regulatory position, so establish the resulting height and storey count early.

Whether the Article 9A fire statement requirement attaches to a prior approval application under Part 20, rather than to an application for planning permission, is a question to put to the authority in writing, because the answer affects the submission. A Fire Statement is a report where a licensed or competent professional is legally required, prepared by someone with the necessary fire engineering competence under the Building Safety Act 2022 framework, and an AI-assisted draft is a starting point for that professional rather than a substitute.

Either way, the design has to deal with escape from the new storeys, firefighting access, the existing stair and its capacity, and the external wall construction of the existing building where new work ties into it.

Noise and disruption to occupiers during works

Building two storeys over occupied flats is the part that generates leaseholder opposition, and Class AA requires a construction management report dealing with it.

What that report needs is the proposed hours of operation, the route and method for deliveries and crane or hoist operation, the measures controlling noise, dust and vibration, the arrangements for maintaining access, lifts, water and power to existing residents, and a communications and complaints procedure. Set it out in a Construction Management Plan with the structural method statement behind it, because the sequence of work is what determines how long residents live with it.

Be realistic in the document. A programme that claims no loss of lift service during a 14-month build will not be believed, and the credibility of the whole submission suffers.

Transport, bins and cycle parking

Transport and highways impacts are within the prior approval matters, so the submission needs to address parking, servicing, refuse and cycle provision for the additional units.

The practical questions are whether the existing parking provision is reduced by the works or by the new units, whether the refuse store has capacity for the additional dwellings and whether the carry distance and collection point still work, whether cycle parking meets the local standard for the additional units, and whether construction vehicles can access the site without blocking the estate road. A Transport Statement covering those points is normally proportionate for a scheme of this size.

But refuse is the one that gets missed. Adding eight flats to a block with a full bin store means rebuilding or extending the store, and that may itself need permission.

What the application must contain

For a prior approval application under Class AA: the plans and elevations of the proposed development including the site location, a developer contact address, the construction management report, a statement addressing each prior approval matter, evidence of the existing building's construction date and height, and the fee. The authority must consult the owners and occupiers of every dwelling in the building.

For a full application: all of the above plus a planning statement, a design and access statement, the daylight and sunlight assessment, structural evidence, the fire statement where the building is a relevant building, and whatever the local validation list adds.

This is general guidance, not legal advice. Permitted development rights, height thresholds and the fire safety regime change, so check the current text of the Order and the 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.