Windows in a flat or maisonette in a conservation area

This page is mainly about England, because the rule that catches flats sits in the English Order. Scotland is genuinely more generous — a Glasgow tenement flat has window permitted development rights a London flat does not — and is dealt with in its own section below. For the whole subject in one place start with the complete guide to conservation area windows; for a house rather than a flat, see do you need planning permission to replace windows in a conservation area?.

The words that do the work

Permitted development rights for houses come from Part 1 of Schedule 2 to the General Permitted Development Order 2015, headed “Development within the curtilage of a dwellinghouse”. Article 2(1) defines that term:

“dwellinghouse”, except in Part 3 (changes of use) … and Part 20 (construction of new dwellinghouses) of Schedule 2 to this Order, does not include a building containing one or more flats, or a flat contained within such a building

The same article defines “flat”:

“flat”, except in Part 20 … or in the expression “flat roof”, means a separate and self-contained set of premises constructed or adapted for use for the purpose of a dwelling and forming part of a building from some other part of which it is divided horizontally

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

Three consequences follow, and all three are commonly missed.

The horizontal division is the test. A maisonette on two floors is still divided horizontally from another part of the building, so it is a flat here. A terraced or semi-detached house divided only vertically from its neighbours is not.

The exclusion catches the whole building, not just the flat — “a building containing one or more flats, or a flat contained within such a building”. A freeholder who owns a converted house containing two flats has no Part 1 rights over the building either.

It applies everywhere in England — conservation area or not, Article 4 direction or not. Government technical guidance says the same in plain words: “Dwellinghouse: does not include buildings containing one or more flats or a single flat contained within a building.”

MHCLG, Permitted development rights for householders: technical guidance — gov.uk, last updated 10 September 2019

The correction that almost every source omits

Because the outcome is usually “you need to apply”, the reason gets compressed into “flats always need planning permission for windows”. That overstates it, and the overstatement costs flat owners money.

Planning permission is required for development and nothing else — section 57(1) of the 1990 Act — and section 55(2)(a) takes a category of work out of that definition altogether:

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

Nothing there turns on tenure, building type or ownership.

Local authority guidance splits on precisely this point. Most publish only the outcome — Camden, for instance, that “If you live in a flat or maisonette, planning permission is required for replacement windows…”. City of York states the rule accurately: “permitted development rights afforded to houses do not apply to other building types like flats or commercial buildings.” And Brighton & Hove gives flat owners the test rather than the outcome: “If you’d like to replace single glazing with double glazing, you won’t need planning permission if there is no change in: material, colour, size, method of opening, design.”

Local planning authority guidance as published; collected 28 July 2026. Brighton & Hove is describing the s.55 test rather than permitted development, without saying so.

That last formulation is not a local concession — it is the section 55(2)(a) test restated as a list of things to look at, and that test applies to every building in England. Islington, which correctly states that “Replacing windows in a flat, a house converted to flats, or a non-residential building is not permitted development”, takes the same line on improvement works in its 2025 window guide: “Improving existing windows (including repair, draft proofing, secondary glazing and replacing glass) does not require planning permission.”

The case that shows the argument is live: a ground-floor flat in a conservation area

That distinction was the whole of the argument in the leading modern judgment on window works.

In London Borough of Haringey v Secretary of State for Housing, Communities and Local Government & Muir, the council issued an enforcement notice dated 21 May 2018 alleging “the installation of UPVC windows on the ground floor front elevation” of 49 Myddleton Road, in the Bowes Park Conservation Area. The house had been divided into flats and the notice was aimed at the ground-floor front bay window of a flat.

The owner appealed on ground (c) — no breach of planning control, because the works were not development at all. Note what that means: the appellant had no permitted development rights to argue about, and did not try to. The whole case ran on section 55. The Inspector allowed the appeal, because around 90% of the front windows in the vicinity were already uPVC, so the installation “has not materially affected the external appearance of the building”. The High Court quashed that decision on 7 November 2019 and remitted it.

Why an Article 4 direction is a red herring for a flat

Article 4(1) of the GPDO works by directing that “the permission granted by article 3 does not apply” to specified development in Schedule 2. Guidance restates the mechanism: “An article 4 direction only means that a particular development cannot be carried out under permitted development and therefore needs a planning application.”

GPDO 2015, article 4(1); Planning Practice Guidance, When is permission required?, Paragraph: 040 Reference ID: 13-040-20140306 — gov.uk

A flat has no Part 1 rights, so a direction covering Class A has nothing to withdraw in relation to it. Practically, the Article 4 register tells you nothing about your own flat: your position is identical either way, and a direction cannot make non-development into development.

It also removes a saving other people get. Northern Ireland’s reduced £78 fee applies where the article 3 permission “does not apply … by reason of and only by reason of … a direction made under Article 4”, and Wales waives the fee on the same basis. A flat meets neither test, because no right was ever withdrawn.

Planning (Fees) Regulations (NI) 2015, reg.7(1); Welsh Government, Fees for planning applications … in Wales from 1st December 2025

What designation does still do to a flat is bite on the merits of any application: in England, section 72(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 requires special attention to the desirability of preserving or enhancing the character or appearance of the area. That duty is why refusals read the way they do — see Article 4 directions and your windows.

Why reglazing is the strongest strategy specifically for flats

For a house, section 55(2)(a) and Class A are alternative routes to lawfulness. For a flat there is only one route, and that changes the economics of the decision.

The strongest version is a new sealed unit fitted into the existing sash or frame with the frame, sightlines, glazing-bar sections, opening arrangement and external profile all unchanged. Those works are plainly for the improvement or alteration of the building, and there is a strong argument that nothing about the external appearance changes to more than a de minimis degree — in which case they are not development at all, and the absence of permitted development rights is irrelevant.

Internal secondary glazing is cleaner still, falling under the interior-only limb in section 55(2)(a)(i) rather than the materiality limb; the Planning Portal lists “installation of internal secondary glazing” among works for which you do not usually need to apply. See secondary glazing, double glazing and vacuum insulated glazing for what actually fits.

There is a building regulations dividend too, in England, where Approved Document L Volume 1 is explicit that “Replacing glazing, or a window or door in its existing frame is not providing a controlled fitting. Such work does not need to meet the energy efficiency requirements.” Replacing the whole unit does. Note what that paragraph does not say: it switches off only the energy efficiency requirements, not safety glazing, ventilation or means of escape. See building regulations for replacement windows.

The hurdles that are not planning at all

The lease. Whether the windows form part of your demise, or are retained by the freeholder as part of the structure, is a question of the wording of your particular lease. There is no general rule, and sometimes glass and frame are treated differently. Read the lease before you get quotations.

Freeholder or managing agent consent. The Planning Portal puts it plainly: “if you are a leaseholder, you may first need to get permission from your landlord or management company.” This is contract, not planning: permission does not override a lease covenant; a licence for alterations is not planning permission and cannot cure the absence of it; the authority will not police your lease and the freeholder cannot enforce planning control; and a section 192 certificate binds the authority, not your freeholder.

Planning Portal, Doors and windows — planningportal.co.uk

Where the building is listed, add a third consent regime on top of planning. In England, section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990 prohibits works of alteration affecting the building’s character as one of special architectural or historic interest unless authorised — with no “materially affects the external appearance” threshold and no exemption for interior work. Listing covers the whole building, so a flat in a listed building is caught even though it has no planning rights to lose.

Applying, when you have to

The evidence bar is joinery-level, and it is local. Lewisham asks for a 1:20 elevation of each window plus 1:5 details of frames and glazing bars including “glazing bars and spacers (if any)”, a vertical section and horn details, noting that “the contractor who is making your windows should be able to supply these drawings”. Torbay requires sections at 1:1. For reglazing, Islington asks instead for product data and a section showing how the unit would be fitted in the existing frame. There is no national standard, so read your authority’s validation list first: drawings, fees and what officers look at.

Fees. We could not verify from a primary source which national fee category a window application on a flat falls into, so we will not state a national figure. One authority’s published figures: Lewisham gives £548 for a flat or an Article 4 house and £1,083 for more than one dwelling — note that the figure for a whole building is not a multiple of the number of flats. Fees change; check before applying.

Lewisham Council, Apply for replacement windows in conservation areas and listed buildings — lewisham.gov.uk, page dated 1 April 2026

The whole-block problem — and the whole-block opportunity

A single flat has a structural difficulty a house never has: your windows are part of a group that reads as one composition, and an officer will judge them that way.

The clearest illustration is a listed building consent appeal rather than a conservation area one, so it shows the mechanism rather than being authority on planning merits. At 19 The Old Police Station, North Park Road, Harrogate — one unit in a Grade II listed conversion — the appellant proposed double-glazed timber sashes retaining the original boxes and replicating the original horned sashes, six-over-six panes and narrow glazing bars. The appeal was dismissed on 17 November 2025, and the reasoning transfers to any flat in a uniform building:

Replacing the glazing would result in the windows appearing visually prominent compared to the existing windows that provide a consistent approach throughout the building.

changing the glazing throughout No 19 would appear incongruent with the rest of the conversion scheme harming the significance of the building.

Appeal APP/U2750/Y/24/3357665, decision 17 November 2025, DL13 — Planning Inspectorate. A listed building consent appeal under s.20 of the Planning (Listed Buildings and Conservation Areas) Act 1990, not a conservation area planning appeal.

Uniformity cuts against the individual flat owner and for the building. The corollary is the opportunity: a programme covering every window in the building answers the incongruity objection, and a consistent scheme is easier to defend than one flat’s change. That is how larger schemes get consent — at Mackworth Green, Finedon, a registered social housing provider took six linked appeals on groups of Grade II listed properties in the Finedon Conservation Area, and all six were allowed on 8 October 2025, including a material the council had resisted, because “no historic fabric would be lost and the overall effect in design terms would be neutral”.

Appeals APP/M2840/W/25/3366353 and five linked appeals, decision 8 October 2025, DL19 — Planning Inspectorate

So if you are one leaseholder among several, the most productive first move is often not an application but a conversation with the freeholder, managing agent or residents’ management company about doing the elevation, or the whole building, as one scheme.

A Scottish flat is in a different position

In Wales and Northern Ireland, Class A is confined to dwellinghouses exactly as in England, so a Cardiff or Belfast flat has no window permitted development rights either. See Scotland, Wales and Northern Ireland.

What to do, in order

1. Establish the building type from the deeds, not the doorbells. Purpose-built block, converted house, maisonette over a shop: all flats. A vertically divided house is not.
2. Read the lease, and ask the freeholder or managing agent in writing before you get quotations.
3. Decide between reglazing and replacement on the planning consequence, not only on price. New glass in the existing sash may take you outside the planning system; new frames will not.
4. Check whether the building is listed. If it is, listed building control covers the whole building including the interior, and the planning answer is only half the question.
5. Photograph everything first — elevations, and close-ups of glazing bars, meeting rails, horns and putty lines with a rule in shot. If materiality is ever argued, that is your evidence.
6. If the sum at stake is large, apply under section 192 rather than relying on an installer’s assurance; and if you must apply for permission, ask about a building-wide scheme first.
7. If the windows are already in, the enforcement position is as for any building: in England, ten years from substantial completion for work completed on or after 25 April 2024, the old four-year period preserved for earlier work, and four years in Wales. See enforcement, time limits and selling the house.

Two claims to stop believing: that the conservation area is why your flat needs permission — the flat is why, and it would be equally true in an undesignated suburb; and that because everyone else in the block already has uPVC yours cannot be material — that argument won at Inspector level in Haringey and was quashed as irrelevant to section 55.

Sources are listed below and on our sources page; terms of art are in the glossary.