Do you need planning permission to replace windows in a conservation area?

This page deals with England. Scotland, Wales and Northern Ireland have different legislation and, in Scotland’s case, a materially stricter starting position — see Scotland, Wales and Northern Ireland. If your building is listed, planning permission is only half the question and the other half is stricter: see windows in a listed building. For the whole subject in one place, start with the complete guide to conservation area windows.

Three questions, not one

Almost every wrong answer about conservation area windows comes from merging three separate legal questions. Keep them apart and the picture is much clearer.

An installer’s FENSA or CERTASS certificate answers the third question only. It is not planning permission and it cannot cure the absence of it. See building regulations for replacement windows.

Question one: is replacing your windows “development” at all?

Planning permission is only needed for development. Section 55(1) of the Town and Country Planning Act 1990 defines that as “the carrying out of building, engineering, mining or other operations in, on, over or under land, or the making of any material change in the use of any buildings or other land”, and section 55(1A) confirms that “building operations” includes structural alterations.

But section 55(2)(a) then takes a category of work back out again:

The following operations or uses of land shall not be taken for the purposes of this Act to involve development of the land — (a) the carrying out for the maintenance, improvement or other alteration of any building of works which (i) affect only the interior of the building, or (ii) do not materially affect the external appearance of the building …

Town and Country Planning Act 1990, s.55(2)(a) — legislation.gov.uk, latest revised text

Two things follow, and both matter.

First, interior-only work is outside the planning system entirely. Internal secondary glazing, draught-stripping, internal shutters: not development, no permission, in any conservation area. The Planning Portal confirms the position for internal secondary glazing directly.

Second, external work escapes only if it does not materially affect appearance. Government guidance is candid that the term is not defined: “The term ‘materially affect’ has no statutory definition, but is linked to the significance of the change which is made to a building’s external appearance.”

Planning Practice Guidance, When is permission required?, Paragraph 001 Reference ID 13-001-20140306 — gov.uk

What the courts have said about “materially”

The leading statement comes from Burroughs Day v Bristol City Council [1996] 1 PLR 78, and was restated by the High Court in 2025 as three propositions: a change must be more than de minimis before it can be material; materiality is context-specific in every case; and the conclusion is a matter for the planning judgement of the decision-maker.

Restated in Dharmeshkumar v SSHCLG & LB Brent [2025] EWHC 25123 (Admin) at [80] — National Archives Find Case Law. Burroughs Day is not itself available online; it is quoted in that judgment at [78].

The most useful sentence for anyone with a period house is Burroughs Day’s observation that what is not a material alteration to the external appearance of a factory may well be a material alteration to the external appearance of an eighteenth-century house — whether or not it is listed or in a conservation area. Sensitivity of the building is part of the judgement, not a separate policy overlay applied afterwards.

The same judgment settled a second point that cuts the other way. Because “building” is defined to include “any part of a building”, the comparison can be made against part of the building rather than the whole of it — so you cannot dilute a change to one elevation by averaging it across a whole terrace.

Haringey at [28]; Town and Country Planning Act 1990, s.336(1)

Where reglazing sits

If a new sealed unit goes into the existing sash or frame, and the frame, sightlines, glazing-bar sections, opening arrangement and external profile are all unchanged, then the work is plainly for the improvement or alteration of the building, and on the face of it nothing about the external appearance changes to more than a de minimis degree. On that analysis it is not development, section 57 is never engaged, and no permission is needed.

That is a real and important route — it is the subject of its own guide, double glazing in a conservation area — but be clear about its limits. It depends on nothing visible actually changing. If the unit forces deeper rebates, thicker glazing bars, the loss of bars or horns, a visible spacer line, or a noticeably different glass, the materiality question is live again and the answer becomes one of fact and degree.

We should also be straight about the state of the authority here: we found no court judgment and no Planning Inspectorate decision that rules on whether reglazing an existing sash is development. The reasoning follows from the statute and is consistent with how the courts approach section 55, and the one authority we found stating it in terms is local authority guidance — Islington’s 2025 window guide, which says that “improving existing windows (including repair, draft proofing, secondary glazing and replacing glass) does not require planning permission”. Anyone telling you it is settled law is overstating it.

Question two: if it is development, is it permitted development?

Where the work does materially affect appearance, it is development and needs permission — but that permission may already have been granted nationally. Article 3 of the General Permitted Development Order 2015 grants planning permission for the classes in Schedule 2. For a house, the relevant class is Class A of Part 1:

A. The enlargement, improvement or other alteration of a dwellinghouse.

GPDO 2015, Sch.2 Pt.1 Class A — legislation.gov.uk

Government technical guidance confirms Class A “covers the enlargement, improvement or alterations to a house such as rear or side extensions as well as general alterations such as new windows and doors”.

The point almost every window company gets wrong

Conservation areas are “article 2(3) land” under the GPDO, and paragraph A.2 sets out what is not permitted on that land. Here it is in full:

A.2 In the case of a dwellinghouse on article 2(3) land, development is not permitted by Class A if — (a) it would consist of or include the cladding of any part of the exterior of the dwellinghouse with stone, artificial stone, pebble dash, render, timber, plastic or tiles; (b) the enlarged part of the dwellinghouse would extend beyond a wall forming a side elevation of the original dwellinghouse; or (c) the enlarged part of the dwellinghouse would have more than a single storey and extend beyond the rear wall of the original dwellinghouse; (d) any total enlargement … exceeds or would exceed the limits set out in sub-paragraphs (b) and (c).

GPDO 2015, Sch.2 Pt.1 A.2 — legislation.gov.uk

Cladding. Side extensions. Two-storey rear extensions. That is the whole of it. A.2 says nothing about windows. Conservation area designation, on its own, does not remove the Class A right to replace the windows in a wall of a house.

The condition attached to Class A

Class A comes with conditions. The one that governs replacement windows is A.3(a): “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”.

Government technical guidance reads that permissively, and says so in terms:

it may be appropriate to replace existing windows with new uPVC double-glazed windows or include them in an extension even if there are no such windows in the existing house. What is important is that they give a similar visual appearance to those in the existing house, for example in terms of their overall shape, and the colour and size of the frames.

MHCLG, Permitted development rights for householders: technical guidance, on condition A.3(a) — gov.uk, last updated 10 September 2019

There is no conservation area carve-out in that passage, because A.2 does not create one. So on a house in a conservation area with permitted development rights intact, uPVC windows of similar visual appearance can be permitted development. That is an uncomfortable conclusion for a lot of published guidance, and it is what the Order and the national guidance say.

Two important caveats. A.3(a) is a condition: if the windows are not of similar appearance, the work was never permitted development, and you are in breach. And “similar visual appearance” for A.3(a) is a lower bar than what an Inspector will accept on the merits if an Article 4 direction has forced you to apply. See uPVC windows in a conservation area for how those appeals actually go.

Roof glazing is different

Windows in a roof are not Class A at all — A.1(k)(iv) excludes “an alteration to any part of the roof of the dwellinghouse”. Roof glazing has to look to Class B or Class C:

• Class B (roof additions such as dormers) is not permitted on article 2(3) land at all, under B.1(f). So a dormer window in a conservation area needs planning permission.
• Class C (other roof alterations, including rooflights) is not excluded on article 2(3) land. It is subject to C.1(b): the alteration must not protrude more than 0.15 m beyond the plane of the original roof slope.

GPDO 2015, Sch.2 Pt.1 A.1(k)(iv), B.1(f), C.1(b) — legislation.gov.uk

That 0.15 m limit is precisely why “conservation rooflights” are specified to sit flush. It is a genuinely useful and under-reported point: a flush rooflight in a conservation area can be permitted development where a dormer never is. An Article 4 direction can still remove the Class C right.

Question three: is it a house or a flat?

Permitted development rights under Part 1 belong to dwellinghouses, and the GPDO defines that term to exclude flats:

“dwellinghouse”, except in Part 3 … does not include a building containing one or more flats, or a flat contained within such a building

GPDO 2015, article 2(1) — legislation.gov.uk

So there is no Class A fallback for a flat, a maisonette, or a house converted into flats — anywhere in England, conservation area or not. If the work is development, you apply.

Be careful with the way this is usually stated, though. It is often written as “you always need permission to replace windows in a flat”, and that is an overstatement. Section 55(2)(a) applies to every building whatever its tenure: interior-only work, and work that does not materially affect external appearance, is still not development in a flat. That is exactly what was in issue in Haringey — a converted house, a ground-floor flat with no permitted development rights, and the entire argument fought over whether the uPVC installation was development at all.

The practical consequence is that flats are the strongest case for reglazing in situ rather than replacing frames, because it is the only route to lawfulness that does not require an application. Note also the separate, non-planning hurdle: if you are a leaseholder you will very likely need your freeholder’s or managing agent’s consent, which has nothing to do with planning. See windows in a flat or maisonette.

Putting it together

How to find out where you stand

1. Confirm the conservation area. Ask the local planning authority, or check the constraints layer on its planning map. There is no single national register of conservation areas — the National Heritage List for England covers listed buildings and other designations, not conservation areas.
2. Ask specifically about Article 4 directions. Ask in writing, name your address, and ask which classes are withdrawn. Many authorities publish a register; the wording of the direction is what matters, not the summary.
3. Read the conservation area appraisal. If it names your window type as characteristic, expect that to be quoted back at you.
4. Check for conditions on past permissions. A condition on a much older consent — often from a conversion or a new-build estate — can remove permitted development rights entirely.
5. Photograph everything before you start. Existing elevations, close-ups of glazing bars, meeting rails and horns, and a rule in shot for scale. If materiality is ever argued, this is your evidence.
6. If it matters financially, get a certificate. Section 192 of the 1990 Act lets you ask the authority to certify that proposed operations would be lawful, and while a certificate is in force the lawfulness of what it describes “shall be conclusively presumed”. That is the only way to turn a salesperson’s confidence into something binding.

If you have already done it

The immunity period in England changed. For operations substantially completed on or after 25 April 2024, no enforcement action may be taken after ten years from substantial completion. The old four-year period is preserved for operations substantially completed before that date, and Wales remains at four years.

Town and Country Planning Act 1990, s.171B(1), as amended by the Levelling-up and Regeneration Act 2023 s.115; commenced 25 April 2024 by SI 2024/452 reg.3(b), with the transitional saving in reg.5

A great deal of published guidance still refers to the four-year rule. See enforcement, time limits and selling the house.

The five claims to stop believing

1. “Conservation area designation removes permitted development rights for windows.” It does not. A.2 restricts cladding, side extensions and two-storey rear extensions.
2. “You always need planning permission for windows in a conservation area.” Not for a house with permitted development rights intact.
3. “An Article 4 direction means you need permission even to change the glass.” A direction withdraws the permission granted by article 3. It cannot make non-development into development.
4. “You need conservation area consent.” It was abolished in England in 2013 and never applied to windows. See conservation area consent for windows.
5. “Everyone else has uPVC, so it cannot be material.” Legally irrelevant to section 55, per Haringey.