Do flats need planning permission for roof windows?

Householders get a set of planning freedoms from the General Permitted Development Order, and altering a roof is one of them. The freedoms are written for dwellinghouses. In its list of definitions, the Order says that a dwellinghouse is not a block containing flats, and not an individual flat inside a block either. The definition in the Order was left unchanged by the amendment that came into force on 21 October 2026.

The effect is simple to state and easy to miss. A flat owner cannot point to the roof alteration right that a house enjoys, because the right does not reach the flat. That does not mean permission will be refused. It means the starting point is a conversation with the council, not an assumption, and in many cases an application. The same is true of a house that has been divided into flats and of a maisonette, which is a flat in the Order's eyes.

Planning control bites only on development, and the Town and Country Planning Act does not treat as development any works that fail to materially affect external appearance. A replacement roof window in an existing opening, the same size and in the same position, may be treated as exempt. A new window cut into a slope that people can see from the street usually does not.

Whether a change is material is a judgement for the council, so for a flat the safest route is to ask. Many councils offer a way to confirm in writing that a proposal needs no permission, and the answer is worth having if you ever sell. Photographs of the existing roof and a simple drawing of the window make the enquiry quick to answer, and a council officer can usually tell from them whether the street would notice the change. Our guide to planning permission for a skylight shows what a house owner can do without asking, for contrast.

Two quite different things get called a flat roof in this question. The first is a roof that is level, such as the top of a block or a rear extension. The second is a roof belonging to a flat, which may be pitched. The planning position follows the building, not the shape of the roof. A level roof on a house is dealt with under the roof alteration right, while a level roof on a block of flats is not.

In a block, the roof is normally shared. A top-floor flat may have a lease that includes only the space below the roof covering, or that includes the airspace and the covering above it. Reading that wording tells you whose permission you need, and a solicitor can confirm it if the lease is old or unclear. A rooflight over a stairwell or a corridor is a matter for the building's owner and its fire strategy. Our answer on flat roof skylights describes the units that suit a level roof, and the upstands they stand on.

Many flats near the seafront and in the older parts of town occupy converted Victorian and Edwardian houses. Those buildings can sit in a conservation area, and a conservation area does not by itself remove the rights a house has. In a flat, there were no such rights to remove, so the council's view of the street scene matters from the start. In Bognor, the Steyne and Aldwick Road areas have terraces with slate roofs and tall chimneys, where the council's own guidance asks for slate and clay roofing to be reinstated where it has been swapped for modern material.

A listed block is stricter. Any alteration that would affect its special character needs listed building consent, and a roof window in a slope people can see is likely to do that. Inside the South Downs National Park, either the Park Authority or the district council acting for it takes the application, depending on the district the flat lies in. The first step is always to find out which designation applies to your address, using the council's planning map.

Planning is not the only approval. A new roof window has to meet Approved Document L, which asks for 1.4 W/m²K from a roof window, and a new opening alters the structure, so building control is involved. In a block of flats, the fire strategy and the structure belong to the whole building, which is why the freeholder or managing agent will want the details. A neighbour's flat sits directly below or beside the opening, so the way the roof is sealed during the work matters to them, and a managing agent may set rules about working hours, access through shared stairs and where materials can be stored.

A sensible order is to read the lease, write to the freeholder, ask the council whether an application is needed, and only then book the work. Photographs come with our survey, then a written quote giving the price as one sum. Our guide to roof windows and the Building Regulations explains what the inspector checks, and our skylights and roof windows page covers the work we do.