Planning permission for a balcony on a flat

Adding a balcony to a flat needs planning permission. There is no size below which it does not, because the permitted development rights that let a house owner build without applying are drafted for a dwellinghouse, and the General Permitted Development Order defines that term so as to exclude flats and buildings containing flats. Even a Juliet balcony, which adds no platform at all, is an external alteration to a flat and therefore development.

What then decides the application is overlooking, and on any taller block, fire. The second of those has become the harder one since the Building Safety Act 2022 changed how external attachments on residential buildings are treated.

Where the permitted development route stops

Part 1 of Schedule 2 to the Order covers extensions, roof alterations, porches and hard surfaces within the curtilage of a dwellinghouse. None of it is available to a flat.

Nor is there a de minimis exception that rescues small works. Councils do sometimes take a pragmatic view of a replacement handrail or a like-for-like repair, but a new balcony changes the external appearance of the building and creates a new area of private amenity space, and both are development.

You will therefore be using the full application form rather than the householder one, which affects the fee band and the appeal route. Check the current fee schedule, because the figures are indexed annually.

Juliet balconies compared with projecting ones

A Juliet balcony is guarding across a door opening, usually a glazed or metal balustrade fixed to the face of the building with no walk-out platform. A projecting balcony is a structure you can stand on.

The planning difference is substantial. A Juliet balcony changes the elevation but adds no vantage point beyond what the window already gave, so the overlooking objection largely falls away. Officers approve them routinely on rear elevations, and the argument is usually about appearance rather than amenity.

A projecting balcony creates a place to stand, closer to the boundary, higher up, and with a wider field of view than a window. That is the change the neighbours object to, and it is a real change rather than a perceived one.

If your scheme is marginal on privacy, the Juliet option is the one that gets approved. It is worth pricing both before you submit.

The overlooking assessment

Councils apply their own separation standards, set out in a residential design guide rather than in national policy. The figure most often quoted is around 21 metres between directly facing habitable room windows, with shorter distances accepted where the outlook is oblique or screened.

The analysis that persuades is drawn, not described. Provide a plan showing the field of view from the balcony edge with the neighbouring windows and private garden areas marked, and a section showing the downward angle into the nearest garden. Where the balcony faces another block across a courtyard, measure the actual distance and put it on the drawing.

Side screens do most of the mitigation work. A balcony with obscure-glazed or solid returns on both flanks looks forward only, which removes the objection from the flats either side while leaving the outlook the applicant wanted. Set the balustrade height and the screen height on the section, because a condition requiring them will refer to that drawing.

Daylight to the flat below is the other technical point. A projecting slab reduces the sky visible from the window underneath it, and on a deep balcony over a north-facing window that can be a real loss rather than a theoretical one.

Materials, combustibility and fire

This is where balcony applications now turn, and it catches householders and architects alike.

Building Regulations requirements restrict the combustibility of materials used in the external walls of relevant buildings, and a balcony attached to an external wall is treated as a specified attachment for those purposes. On buildings above the height threshold, the materials in the balcony structure, its decking and its balustrade have to meet the reaction to fire classification required by the regulations. Timber decking is the product most often specified and then removed at building control stage.

Separately, a planning application for development involving one or more relevant buildings requires a Fire Statement under Article 9A of the Development Management Procedure Order, forming part of Planning Gateway One. Relevant buildings are broadly those of at least 18 metres or seven storeys containing two or more dwellings. Adding balconies to an existing block of that height brings the requirement into play, and the Building Safety Regulator is the statutory consultee.

A Fire Statement has to be prepared by someone with the necessary fire engineering competence. It is one of the report types where a qualified professional is legally required, and an AI-assisted draft is a starting point for that person rather than a substitute for them.

On a three-storey block, none of this applies. Establish the building height early, because it determines whether you are running a straightforward amenity case or a fire safety one.

Fixing a balcony to an existing wall

The structural detail rarely features in the planning decision and frequently kills the project afterwards.

Three questions to answer before you commit:

1. What is the wall made of, and can it take a cantilever? A cavity brick wall in a 1960s block usually cannot without a supporting structure.
2. How is the thermal bridge handled? A steel penetrating the insulation line creates a cold bridge and a condensation risk in the flat below.
3. Where does the water go? An open deck above a window needs a drainage detail that does not discharge onto the glazing beneath.

Self-supporting balconies on posts avoid the cantilever problem and often look heavier. Where the block has a rhythm of recessed bays, sitting the balcony within the recess solves the appearance question and the structural one together.

The Design and Access Statement is the place to explain the chosen approach, particularly where the building sits in a conservation area and the structural solution drives the appearance.

Freeholder and leaseholder consents

Planning permission does not give you the right to alter the building.

In almost every flat, the external walls are retained by the freeholder and the lease either forbids structural alterations or requires written consent. Fixing anything through an external wall touches the landlord's property. Many leases also require the consent of other leaseholders where the works affect the structure or the insurance.

The application itself will expose this. Where you are not the sole owner of all the land within the red line, you must serve notice on the other owner and complete the ownership certificate accordingly. Serving notice is a planning formality, not a substitute for the landlord's consent.

Start the lease consent process at the same time as the application, because licence for alterations negotiations regularly take longer than the eight weeks the council has.

What to submit, and what gets conditioned

Existing and proposed elevations of the whole elevation, not just the affected flat, so the officer can see the balcony in the context of the facade. A plan at a scale showing the balcony, its screens and the relationship to neighbouring windows. A section through the balcony showing projection, balustrade height and the head of the window below. A location plan with the red line drawn over the whole building where the works affect shared structure.

Add a short Planning Statement dealing with privacy, appearance, daylight and, where relevant, fire, and say what conditions you would accept.

Expect conditions fixing the obscure glazing to the flank screens, requiring them before first use, and specifying materials. On taller buildings, expect a condition tying the works to the approved fire strategy.

Browse the report types by category to see what a balcony application on a taller block usually carries. This is general guidance, not legal advice. Check 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.