Do You Need Planning Permission to Add a Window UK?

Adding a window may seem like a simple upgrade, but depending on your property and location, it could require planning permission. Whether you’re looking to brighten a room, convert a garage, or update the look of your home, understanding the legal requirements will help you avoid delays and potential fines.

When Would I Need Planning Permission to Add a Window?

In many cases, adding or replacing a window in a house doesn’t need planning permission because it falls under permitted development rights. However, there are conditions. If you’re installing a new window on the side of your property, it must be fitted with obscure glazing and must not open below 1.7 metres from the floor inside the room. This is to protect the privacy of your neighbours.

Planning permission may be required if the new window significantly changes the external appearance of your home, overlooks neighbouring properties in a way that affects their privacy, or is part of a listed building. If your home is located in a conservation area, national park, or another protected area, extra restrictions may apply. It’s always a good idea to check with your local planning authority before starting work, even if you think the changes are minor.

Can I Add a Window in a Flat?

Flats and maisonettes are treated differently from houses when it comes to planning rules. Permitted development rights do not apply to flats, so any external alteration—including adding a window—requires planning permission. Even if the change seems small, you must go through the formal application process.

In addition to planning approval, you may need to get consent from the building’s freeholder, especially if you don’t own the entire structure. If your lease includes conditions set by a management company or residents’ association, you’ll need their approval too. Always review your lease agreement before proceeding.

Replacing a Garage Door with a Window

If you’re converting a garage into a habitable room and want to replace the garage door with a window, whether or not you need planning permission depends on several factors. If the garage is attached to the main house and the change does not alter the building’s overall footprint, planning permission may not be needed. However, some newer housing developments have specific covenants or restrictions on altering garages, and you’ll need to check if these apply to your property.

If the garage is detached or fronts directly onto the street, planning permission is more likely to be required. Living in a conservation area or owning a listed building also adds extra layers of regulation. Regardless of planning permission, you will need building regulations approval for structural changes and to ensure the new window meets safety and energy standards.

What Are the Rules for Changing Your Existing Frames and Adding New Openings?

If you’re simply replacing existing window frames with similar ones, planning permission is usually not needed. But if you’re changing materials—for example, swapping timber for uPVC—especially in a conservation area, it’s worth confirming with your council to ensure compliance.

When it comes to cutting new openings, such as adding a window to a previously solid wall, the rules are stricter. For houses, this type of work is generally allowed under permitted development as long as privacy conditions are met. For flats, though, any new external opening will need planning permission.

All structural changes must comply with building regulations. This includes verifying that the wall can support the new opening, ensuring the window is safe, meets fire escape rules if required, and offers adequate ventilation. Energy efficiency standards must also be met, particularly if you’re installing double glazing.

Before starting any work, it’s best to consult both a qualified contractor and your local planning office to ensure everything is compliant.

Building Regulations Always Apply

Even if planning permission isn’t required, building regulations always apply. This includes safety glazing in critical areas (like bathrooms or near doors), energy efficiency (double glazing usually meets this), and structural integrity if you’re cutting into a wall. You'll also need to make sure ventilation is maintained — this could mean trickle vents or extractor fans in certain rooms.

Fire Escape Requirements

For bedrooms and some loft conversions, windows must be large enough to act as a fire escape. This means a minimum opening of 450mm in both height and width, and the bottom of the window should be no more than 1100mm above the floor.

Party Walls and Shared Walls

If your proposed window affects a shared wall (like in terraced or semi-detached homes), the Party Wall Act may apply. You might need to notify your neighbour in writing and get a formal agreement.

Leasehold vs Freehold

If you live in a leasehold property, even small external changes usually need permission from the freeholder. This is separate from planning permission, but just as important.

Permitted Development Can Be Removed

In some areas (especially new builds or areas with Article 4 Directions), your permitted development rights might be restricted or removed entirely. Always check with the council — don't assume you’re covered.

Planning Permission Is About Appearance Too

It’s not just about privacy or structure. Planning authorities can object if a new window “doesn’t match the character” of the building or surrounding area. Materials, proportions, and symmetry matter, especially on front-facing elevations.