Sash windows are the most recognisable feature of Victorian and Georgian London. Walk through Islington, Hackney, Hampstead or Kensington and you’ll see them on almost every terrace. When they’re working properly — sliding smoothly, sealing tightly, looking right — they’re one of the best window designs ever made. When they’re not, they rattle, draughts, let in damp and cost a fortune to heat around.
At International Windows Group we manufacture and install timber sash windows across London. New replacements, restoration of existing frames, secondary glazing for listed buildings — we handle the full range. Every window is made to measure in our own workshop.
Browse completed installations in our timber windows portfolio or read more about us on the About Us page.
What Are Sash Windows?
A sash window has two glazed panels — sashes — that slide vertically past each other, traditionally counterbalanced by weights hidden inside the frame. The upper sash drops, the lower sash rises. This allows ventilation from top and bottom simultaneously, which is why the design became so popular in London’s Georgian and Victorian housing stock and why so many of those properties still have them today.
The original timber frames were built to last — and many have, for 150 years or more. The problems come from decades of paint, neglect, failed putty and rotted sills rather than from any fundamental flaw in the design itself. A properly restored or replaced sash window will perform well for decades to come.
For a detailed overview of the style and its history in London, see our guide to Victorian sash windows in London.
Sash Window Services We Offer
Full Sash Window Replacement
When frames are too far gone to restore — rot through the sill, failed joints, distorted boxes — replacement is the right call. We manufacture new timber sash windows to match the profile, sightline width and glazing bar configuration of your originals. Everything is made to the exact dimensions of your opening. See our timber sash windows page for specification details.
Sash Window Restoration
Where the frames are structurally sound, restoration is often the better option — particularly in conservation areas or listed buildings where replacement may not be permitted. We repair rotted sections, replace broken sash cords, re-glaze, re-putty and overhaul the weight and pulley system. The result is a window that looks and operates like new.
Draught-Proofing & Upgrading
If your sash windows are otherwise in good condition but let in cold air, draught-proofing is a cost-effective fix. We fit brush seals to the meeting rail and sides of the sashes, which dramatically reduces heat loss without altering the appearance of the window.
Double Glazing for Sash Windows
Modern slimline double glazing units can be fitted into timber sash frames without significantly increasing sightline widths. This improves thermal performance while keeping the authentic appearance. For properties in conservation areas, we can advise on what’s permitted and what will satisfy your local planning authority.
Sash Windows in London Conservation Areas
A large proportion of London’s housing stock sits within conservation areas or holds listed building status. If your property falls into either category, any window replacement will require planning permission or listed building consent — and the replacement windows will need to match the originals in material, profile and appearance.
We have extensive experience producing sash windows for listed and conservation-area properties. We can advise on specification, help you understand what’s required and supply documentation to support your planning application.
Read our detailed guide to bespoke timber sash windows in North London for more on working in conservation areas, or see our conservation windows page.
Sash Windows Across London
We install sash windows across all London boroughs. We’ve put together area guides for the locations where we work most frequently:
Sash windows in North London — covering Hampstead, Highgate, Islington, Camden, Archway and Finsbury Park, where Victorian and Georgian terraces are most concentrated.
Sash windows in Wembley — a guide to restoration and replacement for the area’s large stock of Edwardian and interwar properties.
Wooden windows in Ealing — Bedford Park, Ealing Broadway, Hanwell and surrounding areas.
Working outside these areas? We cover the full Greater London area. Get in touch to discuss your project.
Timber vs uPVC Sash Windows
uPVC sash windows are cheaper upfront and lower maintenance. For some properties and some budgets, that’s the right answer. We supply them — see our uPVC sash windows page.
But for most London period properties, timber is the better long-term choice. Timber can be repaired rather than replaced entirely. It matches the original character of the building. It’s the only material permitted in many conservation areas and on listed buildings. And a properly maintained timber sash window will outlast a uPVC frame by decades.
The question of which is right for your property is worth discussing before you decide — which is exactly what the free consultation is for.
Glazing & Acoustic Performance
Standard double glazing is available across our sash window range. For properties near main roads, railways or flight paths, acoustic glazing units make a significant difference to interior noise levels. Read our guide to acoustic glazing in London for a detailed breakdown.
If you’re deciding between double and triple glazing, our honest comparison covers the real-world difference in London’s climate: Double vs Triple Glazing in London.
How Much Do Sash Windows Cost in London?
Sash windows are a bespoke product — price depends on window size, number of panes, glazing bar configuration, timber species and glazing specification. There’s no honest single-figure answer, but we’ve put together a detailed cost guide based on real London projects: How Much Do Timber Sash Windows Cost in London? (2026).
For a quick estimate, use our sash windows cost calculator. For North London pricing specifically, see the North London cost breakdown.
Frequently Asked Questions
Can sash windows be double glazed?
Yes. Modern slimline units fit within traditional timber sash frames with minimal change to sightline widths. In most cases the result is visually indistinguishable from single glazed originals. For conservation areas, we advise on what specifications are acceptable to planning authorities.
How do I know if my sash windows need replacing or just repairing?
The key indicators are structural — rot through the sill or bottom rail, failed joints, frames that have moved significantly out of square. Surface deterioration, failed paint, broken cords and draughts are usually repair jobs. We’ll assess this honestly at the consultation stage and recommend the most cost-effective approach. Read our buying guide for more detail.
Do I need planning permission to replace sash windows?
In most cases, replacing like-for-like in a non-listed property outside a conservation area doesn’t require planning permission. In conservation areas or listed buildings, you’ll need consent. We can advise on your specific situation and help with the application if needed.
How long does installation take?
A standard sash window replacement typically takes one day per window. We’ll confirm the timeline at the consultation stage based on your specific project.
Get in Touch
Call us on +44 20 3375 5535 or visit our contact page to arrange a free consultation. We’ll visit your property, assess what’s needed and give you a clear, itemised quote — no obligation. You can also download our technical documentation or browse the product brochures before we speak.