Quick Answer
If your council has an Article 4 direction in place, you need planning permission to replace windows. Most London boroughs do. You'll need timber windows that match the originals in profile, proportions, and glazing bar pattern. uPVC is almost always refused.
When Do You Need Planning Permission?
Living in a conservation area does not automatically mean you need planning permission for window replacement. The key question is whether your council has issued an Article 4 direction.
Without Article 4, window replacement falls under permitted development — you can replace like-for-like without applying. With Article 4, you need a full householder planning application. The critical word is “like-for-like” — the replacements must match the originals in material, design, and proportions.
Most London boroughs have Article 4 directions covering their conservation areas. Islington, Camden, Hackney, Kensington & Chelsea, Westminster, Lambeth, Wandsworth — all have them. If you’re unsure, check your council’s planning portal or call their conservation team directly.
What Conservation Officers Look For
We work with conservation officers across London regularly. Here’s what they actually check when reviewing a window application:
- Material — must be timber. uPVC and aluminium applications are refused in nearly all London conservation areas.
- Profile — the cross-section of the frame, sashes, and glazing bars must match the original. Slim sightlines matter. Chunky modern profiles fail.
- Glazing bars — if the originals had 6-over-6 glazing bars, the replacements must too. Stuck-on bars (common in uPVC) are rejected — they want through-bars or at minimum planted bars with a real shadow line.
- Proportions — the ratio of glass to frame must match. Oversized frames or undersized panes stand out immediately.
- Opening method — sash windows must slide vertically, casement windows must open on side hinges. Tilt-and-turn mechanisms are not accepted as replacements for period windows.
Double Glazing in Conservation Areas
This is where most homeowners get confused. Double glazing is not automatically refused in conservation areas. Most councils now accept slim-profile double glazed units (typically 4/8/4mm or 4/12/4mm) provided the external appearance of the window is unchanged.
The key is that the glazing bars and sightlines must remain slim enough to look like the single-glazed originals. We use slim sealed units specifically designed for heritage applications — 16mm or 20mm total thickness instead of the standard 28mm — which allows us to maintain period proportions while delivering modern thermal performance.
The Application Process
A standard householder planning application costs £258 (2026 rate) and takes 8 weeks for a decision. For window replacements in conservation areas, the process is straightforward if you’re proposing timber like-for-like:
- Submit drawings showing the existing and proposed windows
- Include a heritage statement explaining why the design is appropriate
- Provide material specifications (timber species, paint finish, glazing)
- The conservation officer reviews and either approves, requests amendments, or refuses
We prepare heritage statements and technical drawings for our customers as part of the service. We know what each borough expects and tailor the application accordingly.
What Happens If You Replace Without Permission?
If you install uPVC or non-matching windows in a conservation area with Article 4, the council can issue an enforcement notice requiring you to remove them and reinstate appropriate windows — at your own cost. This is not theoretical; councils do enforce this, particularly in high-profile conservation areas.
We have been called in multiple times to replace uPVC windows that were installed without permission. The homeowner ends up paying twice — once for the uPVC and once for the timber replacements.
See What Conservation-Grade Sash Windows Cost
Design your sash windows in our 3D configurator. All our windows meet conservation area requirements as standard.
Open the 3D Configurator Book a SurveyLondon Borough Requirements
| Borough | Article 4 | uPVC Accepted? | Double Glazing? |
|---|---|---|---|
| Islington | Yes — most areas | No | Yes (slim units) |
| Camden | Yes — most areas | No | Yes (slim units) |
| Hackney | Yes — selected areas | No | Yes (slim units) |
| Kensington & Chelsea | Yes — borough-wide | No | Case by case |
| Westminster | Yes — borough-wide | No | Case by case |
| Hampstead | Yes — most areas | No | Yes (slim units) |
| Richmond | Yes — selected areas | No | Yes (slim units) |
Frequently Asked Questions
Do I need planning permission to replace windows in a conservation area?
Not always. If your council has issued an Article 4 direction removing permitted development rights, you will need planning permission. Without Article 4, you can replace like-for-like under permitted development — but the replacements must match the originals in material and design.
What is an Article 4 direction?
An Article 4 direction is a council order that removes certain permitted development rights in a conservation area. It means changes that would normally be allowed — like replacing windows — now require a full planning application. Most London boroughs have Article 4 directions in place.
Can I install uPVC windows in a conservation area?
Technically you can apply, but uPVC is routinely refused in conservation areas because it does not match the appearance of the original timber windows. Councils require materials that are sympathetic to the character of the area.
How long does planning permission for windows take?
A standard householder planning application takes 8 weeks. If your application is straightforward and matches the original design in timber, approval is usually granted without issues.
Do I need to match the exact original window design?
In most cases, yes. Conservation officers expect like-for-like replacement — same materials, same profile, same glazing bar pattern. Modern improvements like double glazing are usually accepted if the external appearance remains unchanged.