Do You Need Planning Permission for New Windows in London?

You are about to spend four or five figures on windows, and the paperwork question wants settling before you take quotes rather than after. Four facts about your address decide it: listed or not, house or flat, conservation area or not, Article 4 direction or not. You can establish all four yourself in about a quarter of an hour. Everything below is the position in England.

Establish the four facts before you ring anyone

1. Search the National Heritage List for England for your address and the houses either side. Terraces are often listed as a group under one entry, and that entry may not name your number.
2. Open your borough's planning constraints map, sometimes called a policies map. Put your postcode in and read the layers for conservation area, Article 4 direction and listed building. Screenshot it with the date visible.
3. Find the Article 4 direction document itself if one shows. Councils publish the direction with a schedule of the streets it covers, and the wording is the whole thing: some cover front elevations only, some all elevations, some group doors and windows together.
4. Ring the duty planning officer with those three answers in hand. Ten minutes with a specific question beats a week of forum reading. Note the officer's name and the date.

Here is what each fact does.

Most sash work is not development in the first place

Planning control only bites on development. Section 55 of the Town and Country Planning Act 1990 defines the term, and subsection (2)(a) puts outside it works of maintenance, improvement or other alteration which "affect only the interior of the building" or "do not materially affect the external appearance of the building".

That carve-out covers the bulk of what a sash joiner does in a week. New cords and pulleys, splicing sound timber into a rotten cill, re-puttying, easing a sticking sash, brush seals routed into the beads, repainting in the same colour: the outside looks as it did, so none of it is development and none of it needs permission, in any borough. Listed buildings are the exception, dealt with further down. The same reasoning usually extends to a genuine like-for-like replacement, meaning the same timber, section sizes, glazing pattern, opening method and finish.

Where it stops is the word "materially". Timber sashes swapped for uPVC change the material, the sightlines and the way light sits on the surface. A six-over-six replaced by a single sheet of float glass changes the pattern the elevation was designed around. Councils treat those as material changes to external appearance, and once the work is development you need permitted development rights or a permission. It is a judgement of fact and degree, and it is the council's judgement, not yours and not your installer's.

Houses have permitted development rights. Flats have none.

This catches more Londoners than anything else on the list. Permitted development rights for altering a home come from Class A of Part 1 of Schedule 2 to the General Permitted Development Order 2015. Class A applies to a "dwellinghouse", and the Order defines that word to exclude a building containing one or more flats and a flat contained within such a building. Maisonettes count as flats.

So in a flat you have no permitted development rights for window alterations at all, conservation area or not, listed or not. Repair and true like-for-like still sit outside development under section 55, which is why so much flat window work proceeds quietly and lawfully. Change the material or the pattern and you need permission, whatever your neighbour did last year. You will usually need the freeholder's consent under the lease as well, often the slower of the two.

The two Class A conditions that decide window jobs

On a house, Class A permits "the enlargement, improvement or other alteration of a dwellinghouse" subject to limits and conditions. Most of the limits concern extensions; two of the conditions decide window jobs.

Materials of similar appearance

Condition A.3(a) requires that the materials used in any exterior work "must be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse". This decides most window disputes. Timber sash for timber sash of the same profile clears it without argument. A moulded uPVC frame in place of slender painted softwood, with fatter sightlines and a different surface, is the sort of thing councils say does not. Our comparison of uPVC sash windows and original timber covers the visual differences officers actually cite, and if uPVC is what you have in mind, read what councils say about uPVC in conservation areas first.

Upper-floor windows on a side elevation

Condition A.3(b) is narrower than it usually gets quoted, and every qualifier in it earns its place. It applies to "any upper-floor window located in a wall or roof slope forming a side elevation of the dwellinghouse", and requires that such a window be obscure-glazed and non-opening, unless the parts which can be opened are more than 1.7 metres above the floor of the room the window is installed in.

• Upper-floor. A ground-floor window in the same flank wall is outside the condition. It does not have to be obscured and it does not have to be fixed shut.
• Side elevation. Front and rear windows are outside it at every level.
• Wall or roof slope. It catches dormers and rooflights in a flank slope as well as flank-wall windows.
• A condition on Class A work. It attaches to a window you install under those rights, not retrospectively to windows already in the wall.

The government's technical guidance takes obscure glazing to mean at least level 3 on the one-to-five privacy scale glass manufacturers use, and says one-way glass does not count. Get either condition wrong and the work was never permitted development. It is unauthorised development, which is a far less comfortable place to stand than simply having applied.

Conservation area, or conservation area with an Article 4?

Historic England puts conservation area coverage in London at an average of about 17% of land, with some boroughs above half. There is a widespread belief that being inside one by itself means permission for windows. It does not.

Conservation areas are what the Order calls "article 2(3) land". That removes some Class A rights, specifically cladding the exterior, side extensions and two-storey rear extensions. Windows are not on that list. On a house in a plain conservation area with no further restriction, a similar-appearance window replacement can still be permitted development.

What changes the picture is an Article 4 direction: a formal step the council takes to withdraw specified permitted development rights across a defined area, and window replacement is among the most commonly withdrawn. Where one is in force, work that would have been permitted development needs a full planning application instead. Kensington and Chelsea, Westminster, Camden, Hackney and Islington use them heavily and they vary street by street, which is why step three is reading the document rather than trusting the map layer. Our guide to Article 4 directions and what they mean for your windows covers how to read one. A direction never makes work unlawful. It only means you have to ask.

Listed buildings run on a separate track

If the building is listed, a second regime sits on top of everything above. Listed building consent comes from the Planning (Listed Buildings and Conservation Areas) Act 1990, and section 7 prohibits works "for the demolition of a listed building or for its alteration or extension in any manner which would affect its character as a building of special architectural or historic interest" unless they are authorised.

Two things surprise people. Listing covers the whole building, inside and out, so panelled shutters, sash boxes and internal joinery are protected even though nobody sees them from the street. And contravening section 7 is a criminal offence under section 9 of the same Act rather than a planning technicality.

What listing does not do is take away your Class A permitted development rights. The thing that withdraws those across an area is an Article 4 direction, not the listing. The two regimes ask different questions: planning asks whether the outside of the building changes materially, listed building consent asks whether the special interest of the building is affected. So a similar-appearance, timber-for-timber replacement on a listed house can quite properly need listed building consent and no planning permission at all. The two arrive together so often only because most listed London houses also sit in a conservation area, and many of those carry an Article 4 over windows.

Careful like-for-like repair of a listed window is normally treated as maintenance and needs no consent. Replacing the glass, changing the glazing pattern or replacing whole sashes usually does. Only your local authority can confirm which side of the line a job falls, and that answer is not always free. A duty officer will sometimes give a short steer on the phone for nothing, but formal written pre-application advice is charged for across most of inner London: Kensington and Chelsea's householder rate for 2026-27 is just under £600, and listed building enquiries there start at the same figure. Check your own borough's fee page rather than assuming. The written answer is the one worth paying for, because it is the one you can show somebody in ten years' time. Our article on getting listed building consent for windows sets out what a good application contains.

Where your address lands

That last row is the one people misread. Listing and planning run in parallel, so read it alongside whichever row above describes the rest of your situation. A listed house in a plain conservation area keeps its Class A rights; a listed house on an Article 4 street needs both consents; a listed flat needs consent and an application.

The left-hand column is why repairing period windows is administratively so much simpler than replacing them. The law is interested in change, not in upkeep.

Building Regulations are the other regime entirely

Planning and Building Regulations are separate systems with separate people and separate paperwork. A job can need one, both or neither.

Replace a whole window, frame included, and you have provided what the regulations call a controlled fitting. Approved Document L sets the standard for one in an existing home at a whole-window U-value of 1.4 W/m²K, or Window Energy Rating Band B, signed off through FENSA, Certass or building control.

Two things take most sash work outside that. The first is scope. The same document says in terms that replacing the glazing, or a window in its existing frame, is not providing a controlled fitting, and that such work does not need to meet the energy efficiency requirements. Repairs, splices, cords, pulleys, draught seals and paint are well outside it.

The second matters more on the buildings this article is about, and it is the point most quotes leave out. Approved Document L relaxes the energy efficiency requirements for listed dwellings, dwellings in a conservation area and scheduled monuments, where full compliance would unacceptably alter the character or appearance of the building. That is a qualified relaxation and not a blanket pass: the next paragraph says the work must comply where it would not unacceptably alter character, so far as is reasonably practicable, and building control is told to consider the conservation officer's advice on which it is. So "your new sashes have to hit 1.4" is not safe to assert about a designated building until that judgement has been made.

Where character genuinely stops a window reaching that figure, the document names two routes it will accept instead: a centre-pane U-value no worse than 1.2 W/m²K, or single glazing supplemented with low-emissivity secondary glazing. That second route is written into the approved document itself, which is much of why secondary glazing keeps coming up in listed buildings rather than being treated as a compromise. We set out the repair-versus-replace split in building regulations for window work.

If the answer comes back "you need permission"

If the job is expensive or the elevation is prominent, pay for the pre-application advice and get it in writing. If you are relying on permitted development for a change of material on a house, consider a lawful development certificate: a formal ruling that the work is lawful without permission. It carries a fee and takes weeks, and it is a piece of paper you can hand to a buyer's solicitor a decade from now.

Then look hard at whether you need to replace at all. On an Article 4 street, in a flat, or on a listed house, the practical route is almost always to upgrade what is already there. Draught-proofing the existing sashes, new cords, timber splices where the cill or bottom rail has gone, and secondary glazing where the room suits it will get you most of the comfort of a new window with none of the paperwork, because none of it is development and none of it is a controlled fitting. That is what our sash window restoration work consists of most weeks, and our London sash window repair service covers every borough, so we see how differently the same rules land street by street. More often than not, the question of permission turns out not to arise.