Windows and Doors Planning Permission London 2025: When You Need It and When You Don't

**Permitted Development rights for windows and doors — the basic position**:

For most residential properties in England that are not in a designated area (conservation area; National Park; AONB; World Heritage Site) and are not listed buildings, **replacing existing windows and doors is Permitted Development** — no planning permission is required. This applies whether the replacement is like-for-like (timber sash replaced with timber sash) or a material change (timber sash replaced with aluminium casement or uPVC sash), provided the replacement is in an existing opening.

*The legal basis*: Class A of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 permits alterations to the exterior of a dwelling that do not involve a material alteration in the shape of the building, provided certain conditions are met. Replacing a window in an existing opening does not alter the shape of the building — it is therefore PD.

**The conservation area exception — where replacement windows DO require planning permission**:

In a conservation area, Permitted Development rights for replacement windows are frequently — but not universally — removed by an **Article 4 Direction**. An Article 4 Direction is a direction made by the local planning authority that removes specified PD rights in a defined area.

*The critical point*: Article 4 Directions vary by conservation area and by London borough. Not all conservation areas in London have Article 4 Directions removing PD rights for windows. Some boroughs (Westminster; Kensington and Chelsea; Camden; Islington; Hackney) have extensive Article 4 Directions across their conservation areas that include windows; other boroughs have more limited coverage.

*How to check whether windows in your conservation area require planning permission*:

1. Identify whether your property is in a conservation area — check the local authority website or the planning map on the Planning Portal 2. Check whether an Article 4 Direction applies to your conservation area — the local authority conservation area appraisal or the planning portal will list any Article 4 Directions 3. If an Article 4 Direction removes PD rights for windows, you will need **planning permission (householder application; £258)** to replace windows with a different material, style, or glazing pattern — even if the replacement is in the same opening 4. If the Article 4 Direction does not specifically remove window PD rights, replacement windows are still PD in a conservation area — but the choice of replacement must 'preserve or enhance' the character of the conservation area (a test applied in practice by Permitted Development conditions, not as a formal planning application test, but one that can trigger enforcement action if the replacement windows harm the conservation area character)

*What Article 4 Directions typically restrict in conservation areas regarding windows*:

• Where an Article 4 Direction covers windows and external doors, the following typically require planning permission:
• •Replacing timber sash windows with uPVC, aluminium, or composite sash windows
• •Replacing timber casement windows with uPVC casements
• •Adding or removing glazing bars, changing the number of panes, or altering the window pattern
• •Replacing the front door with one of different material, glazing, or design

• *What is typically still permitted even with an Article 4 Direction*:
• •Repainting existing windows in a different colour (internal decoration; not a change to the exterior appearance for PD purposes — but check conservation area guidance)
• •Like-for-like timber sash replacement with timber sash of equivalent appearance
• •Emergency repairs to existing windows that do not alter the external appearance

**Listed buildings — always require consent**:

• For a listed building, **Listed Building Consent (LBC)** is required for any works (internal or external) that affect its character as a listed building. This almost always includes:
• •Any window replacement — even like-for-like — in a listed building
• •Any change to glazing bars, glass specification, opening configuration, or material
• •Any change to external doors
• •Internal secondary glazing that does not affect the external appearance may not require LBC in some cases — check with the Conservation Officer

Listed Building Consent applications are submitted alongside any required planning application (or separately where planning permission is not required). LBC applications: **no fee**.

**New window openings — additional planning considerations**:

Adding a new window in a position where there was no previous window (a 'new opening') is treated differently from replacing an existing window. For most residential properties under PD:

*New windows on front elevations*: generally PD under Class A Part 1, provided they do not project beyond the plane of the existing wall. However, in conservation areas, new front elevation windows almost always require planning permission (where an Article 4 Direction applies or where the new window would harm the conservation area character).

*New windows on side elevations*: a new window on a side elevation of a house (a wall facing a side boundary) can be PD under Class A Part 1, subject to conditions — specifically, any new window on a wall within 1m of the boundary MUST be **obscure-glazed** and **non-opening** (or if opening, the opening must be more than 1.7m above floor level). This is to protect neighbouring properties from overlooking.

*New windows created as part of an extension*: windows created in the new extension walls are part of the extension development. If the extension is PD, the windows within the extension are part of the PD right. If the extension requires planning permission, the windows are assessed as part of the planning application.

**Planning permission for windows — specific scenarios in London**:

| Scenario | Planning permission required? | |---|---| | Replacing like-for-like timber sash; standard residential street (no conservation area; not listed) | No — PD | | Replacing timber sash with uPVC sash; standard residential street (no conservation area) | No — PD | | Replacing timber sash with uPVC sash; conservation area WITH Article 4 removing window PD rights | Yes — householder application £258 | | Replacing timber sash with like-for-like timber sash; conservation area WITH Article 4 | Depends on borough interpretation — some boroughs accept like-for-like as exempt; check first | | Adding new rear elevation window to main rear wall of house; not listed; not conservation area | Generally PD — no PP | | Adding new side elevation window; within 1m of boundary | PD if obscure-glazed and non-opening — but check if conservation area Article 4 applies | | Any window works on listed building | LBC required — always | | New front elevation window changing the design or adding new opening; conservation area | Almost always requires PP |

**Building Regulations apply to all replacement windows — regardless of planning position**:

Even where planning permission is not required for replacement windows, **Building Regulations Part L (Conservation of Fuel and Power) applies** to replacement windows in existing dwellings. Part L requires that replacement windows meet minimum thermal performance standards.

*Part L 2022 replacement window thermal requirements (England)*:

• **Replacement windows (whole window unit U-value — Uw)**:
• •Minimum thermal performance for replacement windows: **Uw ≤ 1.4 W/m²K** (whole unit including frame and glazing)
• •Centre-pane glazing unit (Ug) requirements that are consistent with this: at minimum a double-glazed unit with warm-edge spacer and low-e coating (Ug approximately 1.0–1.2 W/m²K) in a thermally-broken aluminium or uPVC frame (Uf approximately 1.6–2.0 W/m²K) typically achieves a Uw of approximately 1.2–1.4 W/m²K

*Single-glazed historical exceptions (listed buildings and conservation areas)*:

Where a listed building or conservation area building cannot achieve the Uw 1.4 standard without using double glazing that would be inappropriate for the heritage setting (e.g., replacing single-glazed Georgian sashes in a Grade II listed building where double glazing would harm the significance of the building), a relaxation is available. Part L allows a relaxation of the thermal standard where compliance would 'conflict with the character or appearance of a listed building or building in a conservation area'. In practice, this means that like-for-like single-glazed timber sash replacement in a listed building is acceptable from a Part L perspective, provided secondary glazing or other thermal improvement is considered.

**FENSA and CERTASS — self-certification for replacement windows**:

The most important practical aspect of Building Regulations for replacement windows is the **self-certification scheme**. Under Part 11 of the Building Regulations, approved competent person schemes allow authorised installers to self-certify that their installation meets Building Regulations — without requiring a Building Control inspection or application.

• *FENSA (Fenestration Self-Assessment Scheme)* and *CERTASS* are the two main window and door installation self-certification schemes in England. An installer registered with FENSA or CERTASS:
• •Can install replacement windows and doors without a separate Building Regulations application
• •Self-certifies the installation complies with Part L and Part K (safety glazing)
• •Issues the **FENSA (or CERTASS) certificate** to the homeowner at completion
• •Notifies the local authority building control on behalf of the homeowner

*Why the FENSA/CERTASS certificate matters*:

The FENSA or CERTASS certificate is the evidence of Building Regulations compliance for the window installation. When you sell your property, the buyer's solicitor will request compliance evidence for any window replacement works carried out after 1 April 2002 (when the self-certification scheme came into force). Without a FENSA/CERTASS certificate, the only way to demonstrate compliance is through a Retrospective Building Regulations application to the local authority — costing approximately £200–£400 and potentially requiring the installer to revisit and confirm the installation specification.

*What to do if your window installer is not FENSA or CERTASS registered*:

• •Use a FENSA or CERTASS registered installer — this is the simplest and most practical approach for any replacement window installation
• •Alternatively, make a full plans Building Control application to the local authority LABC or Approved Inspector before installation — the inspector checks the window specification before and after installation and issues a completion certificate. Cost: approximately £200–£350 for the application; the process takes 1–3 weeks

**Safety glazing — Building Regulations Part K**:

Part K of the Building Regulations (Protection from Falling, Collision and Impact) requires safety glass in certain glazed areas. The critical zones where safety glazing (toughened to BS EN 12150 or laminated to BS EN ISO 12543) is required:

• *Critical glazing locations requiring safety glass*:
• •Any glazing in doors or sidelights adjacent to doors where the bottom of the glazed panel is less than 1,500mm above the finished floor level
• •Any glazing in the area bounded by: the bottom of the pane less than 800mm above floor level; AND the pane less than 300mm from a door. This covers most glass panels in the lower portion of entrance doors and French doors
• •Any glazing within 800mm of the floor in a staircase or landing area

*Glazing in critical zones that is NOT safety glass must be upgraded*: Replacement windows installed in critical safety glazing zones must use safety glass. A FENSA-registered installer will specify the correct glazing for the position.

**Obscure glazing requirements — windows overlooking adjacent properties**:

As noted above under planning permission, new windows on side elevations within 1m of a boundary must be obscure-glazed and non-opening (or opening above 1.7m) as a Permitted Development condition under Class A Part 1. This is a planning condition — not a Building Regulations requirement — but is frequently confused with the Part K safety glazing requirement.

*Obscure glazing levels*: the planning condition requires Level 4 or Level 5 obscure glazing — sufficient opacity that individual persons cannot be identified through the glass. Level 1 or Level 2 (light diffusion only) does not meet the obscure glazing condition for planning purposes.

*Important clarification*: the obscure glazing condition applies to new windows in a side wall within 1m of the boundary. It does NOT apply to replacement windows in existing openings that are already in use — if your existing side window is clear-glazed, the replacement does not require it to be obscure-glazed unless your planning permission specifically requires it as a condition (which some planning permissions do for extensions that include side windows).

**The conservation area window replacement dilemma in London**:

For homeowners in London conservation areas (which cover a very large proportion of Victorian and Edwardian terrace residential streets in inner and mid London), the question of replacing windows triggers a combination of planning restrictions, conservation area character requirements, and thermal performance obligations that can appear contradictory. In practice, the resolution is a matter of choosing the right replacement window specification.

**Why uPVC windows are almost universally rejected in conservation areas**:

The predominant window type in London Victorian terrace houses is the timber vertical sliding sash window — a double-hung arrangement where both the upper and lower sashes slide vertically past each other in the window frame. This window type is characteristic of the period, the streetscape, and the architectural character of London's Victorian conservation areas.

• uPVC vertical sliding sash windows (often marketed as 'authentic-look uPVC sash') have historically been refused planning permission in conservation areas across London for several reasons:
• •**Sightline width**: uPVC sash windows have inherently wider frame profiles (the box frame housing the sash mechanism) than timber sash originals — the wider sightlines create a different visual proportion that changes the appearance of the window opening
• •**Reflectivity**: uPVC frames have a surface reflectivity and sheen that is different from the matt painted timber of original sash windows — this is visible at street level and is consistently identified by Conservation Officers as a material difference
• •**Lack of authentic detail**: original timber sash windows have a characteristic meeting rail (the horizontal bar where the upper and lower sashes meet); glazing bar configurations (2-over-2; 6-over-6; or other period configurations); and narrow stiles that uPVC manufacturers typically cannot replicate precisely

*The exception*: some conservation areas in London have planning authorities that accept 'slim-profile' or 'heritage-style' uPVC sash windows where the visual difference from the original is judged acceptable. This varies significantly by borough and by Conservation Officer. Do not assume uPVC is acceptable in a conservation area without checking the specific position with the local planning department.

**Acceptable replacement window materials in London conservation areas**:

*1. Timber sash windows (the preferred and most commonly accepted option)*:

Soft timber (redwood; pine) or hardwood (accoya acetylated timber; sapele; meranti) replacement sash windows that replicate the original profile, glazing bar arrangement, and proportions of the existing windows are the standard acceptable replacement in conservation areas. Redwood sash windows require painting (initial paint finish; repainting approximately every 5–7 years); hardwood and accoya timber windows are more durable and accept paint or stain with longer cycles.

• Cost for timber sash window replacement (supply and installation per window in London 2025):
• •Redwood timber sash; double-glazed with slim sealed unit (slimline DGU): £900–£1,800/window
• •Accoya timber sash; double-glazed with slimline DGU: £1,300–£2,500/window
• •Hardwood timber sash (sapele); double-glazed with slimline DGU: £1,100–£2,200/window

*Slimline double-glazed units (for conservation area timber sash windows)*:

Standard double-glazed units (24mm total thickness: 4mm glass, 16mm cavity, 4mm glass) are too thick to fit in original Victorian timber sash frames, which are designed for single-glazed 3–4mm glass. Slimline sealed units (designed for use in conservation areas and period windows) are available in thicknesses of 6.4mm–16mm total, using a vacuum or warm-edge spacer with very thin glass.

• Slimline unit specifications for conservation area sash windows:
• •6.4mm vacuum glazing unit (Pilkington Spacia; other vacuum IGUs): equivalent thermal performance to standard double glazing in a 6.4mm total thickness. Allows the original timber beads and frame to be retained without modification
• •12mm slimline sealed unit (4mm glass; 4mm argon-fill cavity; 4mm glass; warm-edge spacer): less thermally efficient than standard DGU but fits most original sash frames with minor bead modification. Ug approximately 1.8–2.2 W/m²K

*Note on Part L compliance for slimline units*: the slimline units specified for conservation area sash windows typically do not achieve the Uw 1.4 W/m²K threshold required by Part L 2022 — particularly the 12mm slimline units. As noted above, Part L allows a relaxation for conservation area and listed building properties where compliance would conflict with the character of the building. This relaxation should be documented in writing with the local authority Building Control before installation.

*2. Aluminium sash windows ('Crittall-style' or slim aluminium)*:

Thermally broken slim aluminium sash windows (manufactured by companies such as Crittall; Clement Windows; Vufold) are accepted in many London conservation areas — particularly for properties that are not on prominent street frontages or where the original windows were not traditional timber sash. Slim aluminium windows achieve the thermal performance required by Part L (typically Uw 1.2–1.6 W/m²K depending on glazing specification) and have very slim sightlines (the frame profile in section) compared with uPVC or standard aluminium systems.

**Windows in listed buildings — a special case**:

• For Grade I and Grade II* listed buildings, window replacement is extremely tightly controlled. Like-for-like single-glazed timber sash replacement is the standard acceptable approach. Secondary glazing (a second layer of glazing on the inside face of the existing window, in a separate frame) is frequently the recommended approach because it:
• •Does not alter the original window (which is retained)
• •Provides a significant thermal improvement (achieving effective Uw of 1.4–1.8 W/m²K for the combined original window plus secondary glazing, versus Uw 4.8–5.8 W/m²K for single-glazed original windows alone)
• •Does not require LBC in most cases (it is an internal alteration that does not affect the external character of the building)

Cost of secondary glazing in London 2025: typically £350–£700 per window for magnetic or lift-out secondary glazing panels; £600–£1,200 per window for sliding or hinged secondary glazing frames.