Conservation areas, Article 4 and listed buildings
Repairing and draught-proofing sash windows almost never needs permission, but changing them can. This page explains the difference.
What a conservation area actually restricts
A conservation area is an area the local council has designated for its special architectural or historic interest. Large parts of central and north London are covered by them. Designation does not stop you repairing your windows. Its effect is on change: some work that would not need planning permission elsewhere does need it inside a conservation area, and the demolition of buildings within one is controlled.
For windows, the key idea is permitted development. A house has certain rights to alter itself without a planning application, and these include replacing windows with new ones of similar appearance. Flats and maisonettes do not have these householder rights, so changes to their windows can need planning permission wherever they are.
Repair and maintenance that does not change the appearance of the building, using the same kinds of materials, does not need permission. Restoring a sash window, re-cording it, splicing rotten timber, reglazing like for like and fitting draught-proofing all fall on that side of the line. The question only arises when the window itself, or the way it looks, is going to change.
The myth that costs people money
Most firms will tell you that being in a conservation area means you need planning permission to touch your windows. That is not what the law says. Conservation area designation on its own does not remove the right to replace windows on a house. What removes it is an Article 4 direction covering your address, or the building being listed. Westminster City Council's own guidance says permission is needed where new windows would not be of similar appearance to the existing, or where permitted development rights have been removed. Islington's says the same, and adds that its Article 4 directions apply to the front of the house and to sides visible from the street. Directions apply to named streets rather than whole boroughs, so two houses on the same road can be in different positions.
Article 4 directions and why they matter for windows
An Article 4 direction is made by the council, or occasionally by the Secretary of State, to withdraw specified permitted development rights in a defined area. In conservation areas they are commonly used to bring alterations to windows and doors on the street side of houses under planning control, because those are the small changes that gradually wear away a street's character.
Where a direction covers your house, replacing your windows, even with ones that look similar, may need a planning application that would not otherwise be required. Directions vary: some cover only front elevations, some also take in roofs, doors, boundary walls or the painting of brickwork, and each applies to a defined list of addresses or a mapped area.
You can find out whether your street is covered from the council's planning pages, which usually publish conservation area maps, appraisals and Article 4 directions together, or by asking its planning or conservation team. We check at the survey and tell you what we find.
An Article 4 direction does not affect restoring or draught-proofing your windows.
Listed building consent
If your building is listed, the rules are stricter. Listing normally covers the whole building, inside and out, and any work that would affect its character as a building of special architectural or historic interest needs listed building consent from the council. Carrying out such work without consent is a criminal offence.
For windows, this means replacement almost always needs consent. So, in most cases, do double glazing, replacing historic glass with modern glass, and alterations to glazing bars, horns or the opening method. Shutters, shutter boxes and panelled reveals are part of the listed building as much as the sashes are.
Like-for-like repair is a different matter. Splicing a sash with matching timber, renewing cords, reputtying and repainting are maintenance, and maintenance that does not affect the building's character does not need consent. Draught-proofing is in practice not treated as an alteration, because nothing is removed and nothing is visible.
Where consent is needed, the application comes first and the work follows once it is granted.
What councils look at
Every London borough sets its own guidance, so check your council's current guidance before relying on any general picture, including this one.
Repair and draught-proofing change nothing externally, and like-for-like repair is maintenance that does not need permission.
Where replacement does need an application, the council looks at whether the new window matches the original: the material, the section, the opening method, the glazing bar pattern, and horns where the original had them and not where it didn't. In a listed building the case for replacement also has to be made.
Slimline double glazing fitted into the existing sashes keeps the window and its appearance from the street. Whether it needs an application depends on the address, because an Article 4 direction or listing can require one. Secondary glazing, a separate inner pane, leaves the window itself unaltered. Acoustic glass, a single laminated pane in the existing sash, changes nothing from the street.
There is no ban on double glazing
No rule in UK planning law bans double glazing in a conservation area. A council can refuse a particular application on appearance grounds, and many will refuse a standard sealed unit that changes the sightlines. That is a judgement about that window, not a blanket prohibition.
Changes that alter appearance
The changes that most often need an application are the ones that alter how a window looks from the street.
Replacing timber sashes with plastic or aluminium changes the material. These frames cannot match the section of a timber sash, and they often change how the window opens or how it is divided. Standard double-glazed units, at 24 to 28 mm thick, need a heavier modern sash and often glazing bars stuck to the face of the glass, which changes the sightlines.
Changes to the pattern of the window are another: six-over-six sashes replaced with one-over-one, horns added to a Georgian window that never had them, sliding sashes swapped for casements, or historic glass replaced with modern float glass.
In a listed building, removing original sashes that could be repaired has to be justified in the application.
How we support an application
Most of our work needs no application at all. Where yours does, we tell you at the survey which windows are affected and whether we expect planning permission, listed building consent, or both to be needed.
That advice, at the survey, is free. Where an application needs drawings of the existing and proposed windows, we can prepare them as separate work, and we quote for it before we start. Drawings for slimline double glazing show the unit thickness and how it is fixed, because that is what an officer will ask about. Where an architect is already involved, we work with them.
Conservation approved: our methods are accepted by conservation officers across London boroughs. Article 4 streets and listed buildings are our normal work. That does not mean an application will be approved.
Where work needs consent, we wait for it before we start.
How to check your own address
Every London borough publishes a conservation area and Article 4 map. Find your address on it, note whether a direction applies and what it covers, and check the listing status separately on the National Heritage List. If you want, send us what you find with your survey photographs and we will tell you what it means for your windows.
Who to call for independent advice
Sometimes you need advice before you need a contractor: for a purchase, a dispute, a consent application with a lot riding on it, or simply a second opinion on whether your windows can be saved.
For that we refer clients to Heritage Window Consultants. They carry out window condition surveys for listed and period properties, from a single house to an estate; prepare measured drawings and heritage statements for planning and listed building consent applications; and advise on what conservation areas permit. They also offer a digital window survey from photographs or video.
Heritage Window Consultants is the advisory practice of The Barnsbury Group, of which we are also part. Its surveys and reports are written as advice, and you are under no obligation to use us for the work that follows.
For the planning position on a particular address, your council's planning or conservation team is the authority. Most councils publish conservation area maps, appraisals and Article 4 directions on their websites, and the Planning Portal sets out the national rules on permitted development and listed building consent.
Book a survey
Send us photographs of your windows and we'll tell you what needs doing and what doesn't, with a written quotation. The digital survey is free.