Sash Window Replacement London

Sash window replacement in London typically costs £1,200–£4,000 per window depending on size, timber choice, and glazing specification. Accoya® timber with slimline double glazing sits at the higher end but is the best long-term investment. Treated softwood is the most budget-friendly option. We provide a fixed written quote after a free site survey — no surprises on the day.

Installation of a single replacement window typically takes one day on site. Lead time for manufacture is usually 4–8 weeks from order, depending on your specification and our current workload. We'll give you a clear timeline at the survey stage. Most full-house projects on London Victorian terraces are completed in two to three days on site.

Yes — we specialise in conservation area and listed building replacements across all London boroughs. We manufacture period-correct windows that match the original profile, proportions, and glazing bar pattern exactly, satisfying planning requirements. We can advise on any consents required during your free site survey and provide specifications for your local authority if needed.

We always recommend repair where possible — it's cheaper and preserves original fabric. Replacement is the right call when timber is too far gone to save, when the existing window is not original to the property, or when the client requires double glazing in a frame that cannot accommodate it. We will always give you an honest recommendation after assessing your windows — we will never push replacement when repair is the right call.

Yes — we fit slimline A-rated double-glazed units into all our replacement windows as standard. We use slim-profile units that retain the traditional single-glazed appearance and are accepted by most conservation authorities. For maximum thermal and acoustic performance, we also offer vacuum glazing units. See our double glazed sash windows page for more detail.

Yes — Golden Ratio Sash Windows & Doors is FENSA registered. All replacement window installations come with FENSA certification, which is a legal requirement in England and Wales confirming that work complies with Building Regulations. You'll need this certificate for your property records — especially when you come to sell.

Accoya® is a modified softwood that has been treated through a non-toxic acetylation process, making it dimensionally stable and highly resistant to rot, swelling, and shrinkage. It carries a 50-year anti-rot guarantee above ground — significantly outperforming standard softwood or hardwood. It is approved by English Heritage and leading conservation bodies, making it ideal for period property replacements. We are an approved Accoya® manufacturer.

In most cases, like-for-like replacement of sash windows does not require planning permission. However, if you live in a Conservation Area or a Grade II Listed Building, you will likely need Listed Building Consent or prior approval from your local authority before replacing windows. We advise on this during your free site survey and can provide technical specifications if required. We recommend checking with your London borough council early in the process.

We cover all of Greater London. We have strong experience across North London (Islington, Hackney, Haringey, Camden, Finsbury Park, Stoke Newington, Highbury, Holloway, Hornsey, Muswell Hill, Archway), Central London, and West London (Kensington, Notting Hill, Chelsea). Contact us to confirm coverage for your specific postcode.

Yes — all our installations are fully guaranteed. Accoya® timber carries a 50-year manufacturer's anti-rot warranty above ground. Our double-glazed units come with a 10-year seal guarantee. All joinery and installation work is covered under our workmanship guarantee. We are fully insured and FENSA registered. Please review our terms and conditions for full details.