In short: if your property is a listed building, you need Listed Building Consent before replacing any sash window, full stop. If it’s in a conservation area, it depends on whether an Article 4 Direction applies — common in boroughs like Kensington & Chelsea, Westminster, Camden, Hackney and Islington. Without Article 4, like-for-like timber replacement is usually permitted development. With it, you’ll need planning permission even for identical replacements. This guide explains exactly where you stand before you order new windows.

Listed Buildings: Consent Is Always Required

If your home is a listed building — Grade I, Grade II* or Grade II — you must obtain Listed Building Consent before replacing sash windows, and this applies to internal as well as external windows. Carrying out the work without consent is a criminal offence, not just a planning breach, and can result in enforcement action requiring you to reinstate the original windows at your own cost.

Consent applications for listed buildings typically need to demonstrate that the replacement matches the original in material, profile, glazing bar pattern and even paint colour. This is one of the main reasons homeowners choose bespoke timber sash windows built to match historic proportions, rather than off-the-shelf alternatives.

Conservation Areas: Does Article 4 Apply to Your Street?

Conservation area status alone does not automatically remove your permitted development rights. What matters is whether an Article 4 Direction has been applied to your specific street or area.

• With an Article 4 Direction: planning permission is required for any change to windows, even an exact like-for-like replacement in the same material and design.
• Without an Article 4 Direction: like-for-like replacement is usually permitted development and does not require an application.
• Either way: replacing original timber sash windows with uPVC is rarely approved on front elevations in a conservation area, Article 4 or not.

Article 4 Directions are commonly applied in Kensington & Chelsea, Westminster, Camden, Hackney and Islington, but individual streets in almost any London borough can be covered. The only reliable way to check is to search your address on your local council’s planning portal or call their conservation team directly.

What You Can Usually Do Without Permission

Outside Article 4 areas and away from listed buildings, the following typically don’t require an application:

• Repairing or draught-proofing existing sash windows rather than replacing them
• Replacing timber sash windows with matching timber sash windows, same design and glazing pattern
• Internal secondary glazing, which generally falls outside planning control altogether

What almost always needs permission, Article 4 or not: changing the window material on a front elevation, altering the glazing bar pattern, or changing from sash to casement on a period property.

How to Check If Your Property Is Affected

Before ordering any windows, check three things: whether your property is listed (searchable on the Historic England National Heritage List), whether it sits in a conservation area, and whether an Article 4 Direction applies. Your local council’s planning department holds the Article 4 register, and the Planning Portal is a useful starting point for understanding the general permitted development rules before you contact them.

If you’re unsure, we’d always recommend contacting your local authority for written confirmation before committing to an order — a five-minute phone call can save months of delay later.

What Happens If You Replace Windows Without Consent

Unauthorised works to a listed building or in breach of an Article 4 Direction can result in an enforcement notice requiring the windows to be removed and the original design reinstated, at the homeowner’s expense. In the case of listed buildings, it can also be treated as a criminal offence. Insurers and conveyancing solicitors also routinely ask about consent history when a property is sold, so unauthorised replacements can complicate a future sale.

Why This Usually Means Timber, Not uPVC

In the overwhelming majority of conservation area and listed building cases, the only material that gets approved for front-facing windows is timber, built to match the original sightlines and glazing bar spacing. This is worth knowing before you get quotes — if you’re comparing materials, our guide on double vs triple glazing covers how modern timber sash windows can still meet current thermal performance expectations without changing the appearance planning officers are trying to protect.

For a sense of what a compliant replacement project costs, see our guide to timber sash window costs in London.

Need Help Navigating Conservation Area Rules?

We work across London’s conservation areas every week and can usually tell you within a short conversation whether your project needs an application, and what specification is likely to be approved. Get in touch for a free, no-obligation site visit and quotation.