Altering windows: do I need planning permission?

 

Changing the windows on a house is one of those jobs that is often described as “like for like” even when the replacement is actually a different colour, frame material, glazing pattern or size. That can make the planning position less obvious than it first appears.

We already have a broader guide to windows and doors. This page concentrates on the question people usually ask us separately: can I alter or replace the windows I already have?

The answer again has two stages. First decide whether the work materially affects the external appearance and is therefore development. If it is development, a normal dwellinghouse can often rely on Part 1 Class A.

 

 

Is replacing a window development?

 

Section 55 of the Town and Country Planning Act 1990 excludes building operations which do not materially affect the external appearance of a building from the definition of development.

That means a genuinely close replacement window can be outside planning control altogether where the change does not materially affect the external appearance. You do not need permitted development rights for work which is not development in the first place.

But “replacement” is not a magic word. A change from slender timber sash windows to much heavier frames, the removal of glazing bars, a striking colour change, or a substantial change in the proportions of an opening may materially alter the appearance. Whether it does is a matter of fact and degree.

If the alteration is development, the next question for a house is whether Class A grants planning permission.

 

Window alterations under Part 1 Class A

 

Class A covers the enlargement, improvement or other alteration of a dwellinghouse. Government householder permitted development guidance expressly gives new windows and doors as examples of general alterations which can fall within Class A.

The important Class A condition for most window work is that materials used in exterior work must be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse.

That does not mean the material must be identical. The government guidance gives the useful example that uPVC double-glazed windows may be appropriate even where the existing house has no uPVC windows, provided the replacement gives a similar visual appearance – for example in its overall shape and the colour and size of the frames.

Class A is not available where the dwellinghouse was created only by virtue of Part 3 Classes G, M, MA, N, P, PA or Q, or where the dwellinghouse was built under Part 20. Householder Part 1 rights also apply to dwellinghouses, not flats.

 

Changing the colour, material or style of a window

 

There is no GPDO rule saying every replacement window must be precisely the same colour, material or design. Instead, work through the two tests in order:

• does the alteration materially affect the external appearance so that it amounts to development?
• if it is development and you are relying on Class A, are the materials of a similar appearance to those used on the existing dwellinghouse?

A small change of frame colour may not materially affect the building at all. A more noticeable change may amount to development; if it does, it can only rely on Class A where the similar-appearance condition and all the other relevant limitations and conditions are genuinely satisfied. The answer depends on the finished appearance, not just the manufacturer’s description of the frame.

This is one reason why an informal “like for like” label can be misleading. Planning law looks at what actually changes on the building.

 

Making a window larger, smaller or creating a new opening

 

Changing the size or position of an opening, or inserting an entirely new window, is much more likely to amount to development. It can nevertheless fall within Class A if all of the relevant limitations and conditions are met.

There is no blanket Class A ban on altering windows in the front or principal elevation. The principal-elevation restriction in Class A applies where an enlarged part of the dwellinghouse would extend beyond the relevant wall. An ordinary flush window alteration is not an enlarged part simply because it is on the front.

A projecting bay window is different. It enlarges the dwellinghouse. If it projects beyond a wall forming the principal elevation of the original dwellinghouse, Class A will not permit that enlargement.

Similarly, reducing an opening and infilling part of it with brick or another external material can engage the Class A similar-appearance condition. The window and the surrounding wall should be considered as the actual works proposed.

 

Side windows and the 1.7 metre rule

 

Class A has a specific privacy condition for any upper-floor window in a wall or roof slope forming a side elevation of the dwellinghouse. To be permitted development under Class A it must be:

• obscure-glazed
• non-opening unless the parts which can be opened are more than 1.7 metres above the floor of the room in which the window is installed

The GPDO itself does not prescribe a numbered privacy-glass rating. Government technical guidance says side windows should normally achieve at least level 3 obscurity, but the statutory test is the wording in Class A itself.

Rooflights and roof windows are normally considered under Part 1 Class C rather than Class A.

 

Conservation areas and Article 4 directions

 

Being in a conservation area does not, on its own, remove the ordinary Class A right to alter windows. The special Class A restrictions on Article 2(3) land do not contain a general prohibition on window alterations.

However, window controls are a common reason for an Article 4 direction in a conservation area. A direction can remove the Class A right for specified alterations, and the exact wording and geographical area of the direction matter.

A condition on a previous planning permission can also remove or restrict permitted development rights. This is especially common on newer developments where the authority wanted to retain control over elevations, openings or external materials.

 

Listed buildings are different

 

If the property is a listed building, the planning-permission question is separate from listed building consent. Replacing or altering windows will require listed building consent where the works affect the building’s character as a building of special architectural or historic interest.

Window profile, frame material, glazing bars, glass, opening method and historic joinery can all be important. Do not assume that a visually similar replacement, or something described by an installer as “like for like”, automatically avoids listed building consent.

 

What about flats?

 

Part 1 Class A rights apply to dwellinghouses, not flats. That does not mean every replacement window to a flat needs planning permission: a replacement which does not materially affect the external appearance can still fall outside development under section 55.

But where a window alteration to a flat does materially affect the external appearance, or a new opening is created, there is no Part 1 Class A fallback. Planning permission may therefore be required. Leasehold and freeholder consent are separate matters as well.

 

Building Regulations and certificates

 

Replacement windows can also be subject to Building Regulations. That is a separate regime from planning permission, so a planning answer does not replace the need to deal with building control requirements.

If you want a binding planning decision before altering the windows, you can apply for a certificate of lawfulness of proposed use or development (CLOPUD) under section 192 of the Town and Country Planning Act 1990. This can be particularly useful where there is a significant colour, material or design change and you want certainty about whether the proposed operations are lawful for planning purposes.

Planning Geek can review the planning history, any Article 4 direction and the permitted development position and prepare the appropriate application if required. Please complete our fee proposal form if we can help.

 

Page Created: 28th August 2026

Other Common Projects