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Most London homeowners ask this question when their sash windows start to fail. The honest answer depends on condition, budget, and whether planning restrictions apply — not on what is most profitable for the contractor. This guide helps you make the right call.
In the vast majority of cases involving Victorian, Edwardian, or Georgian sash windows in London, repair and restoration is the better option. Original timber sash windows were made from old-growth softwood that is denser and more durable than anything available today. With the right work, they can last another century. Replacement is rarely the only option — but it is sometimes the right one.
The question is almost never “are these windows worth saving?” — original period sash windows almost always are. The real question is whether the condition of your specific windows still makes repair economically viable, or whether the extent of failure means that replacement delivers better long-term value.
This guide sets out the factors honestly. We carry out both repair and replacement, so we have no reason to push you either way.
Repair makes sense when the core structure — the box frame, the pulley stiles, and the main frame members — is still intact and sound. Individual components fail long before the frame does, and those components can be replaced without touching the frame.
Cheap and fast to replace. No reason to consider replacement.
Splice repair or component replacement — the frame itself stays.
Draught proofing with brush seals eliminates this at a fraction of replacement cost.
Swollen timber, paint build-up, or jammed cords — all fixable without replacement.
Slimline double glazed units can be retrofitted into original frames.
Repair is often required. Replacement may not be permitted.
The environmental case: Retaining an existing window avoids all the embodied carbon of manufacturing a replacement. Restored timber sash windows have a significantly lower whole-life carbon footprint than uPVC or aluminium alternatives, even when energy performance is factored in.
A properly restored sash window is not simply one that has been painted and had its cords replaced. Full sash window restoration typically includes:
A window that has had all of this done will perform as well as — and often better than — a new replacement window in the same opening, at a cost that is typically 30–60% lower.
There are situations where repair is not viable and replacement is the honest recommendation. We will tell you if your window falls into this category during the free site survey.
If the pulley stiles, head, or sill plate are rotten to the core, there is nothing left to repair into. Replacement is the only sound option.
Where mortice and tenon joints have separated and the frame is no longer square or rigid, restoration becomes uneconomic.
Windows that have been repeatedly filled, bodged, and painted over may be beyond economic repair. The cost to strip and restore correctly may exceed replacement.
If a previous owner fitted cheap softwood replacements of poor quality, these may not be worth restoring. A like-for-like timber replacement in Accoya or hardwood makes more sense.
When we replace a sash window at Golden Ratio, we always recommend a like-for-like timber replacement — not uPVC. A new timber sash window can be built to exactly match the profile, proportions, and detailing of the original, maintaining the character of the property and meeting listed building and conservation area requirements.
Our replacements are built in hardwood or Accoya as standard, with slimline double glazing as an option, and are finished and installed by the same team. See our sash window replacement page for full details.
If your property is listed or in a conservation area, the decision may be made for you. Listed building consent is required to replace windows, and it is not always granted — particularly if the existing windows are original. Repair and restoration is usually required.
In conservation areas, replacement is often permitted but will be subject to conditions on material and appearance. uPVC is almost never acceptable in a conservation area. Timber — matching the original profile — is the only compliant option if replacement is approved.
The numbers below are indicative. Exact costs depend on window size, condition, number of windows, and specification. We provide a full written quote after the free site survey.
uPVC sash windows are cheaper upfront. They are also, in our view, the wrong choice for a period London property. uPVC cannot replicate the slim sightlines, the flush meeting rail, or the proportions of an original timber sash. It cannot be painted to change colour. It degrades in UV light and becomes brittle and difficult to repair. And it cannot be used on listed buildings or, in most cases, in conservation areas.
The long-term cost of uPVC — reduced property value, replacement every 20–25 years, planning complications — typically exceeds the cost of a quality timber restoration or replacement. We do not install uPVC.
Yes, in most cases. Victorian and Edwardian sash windows were made from dense, slow-grown timber that is more durable than modern softwood. The box frame construction means individual components can be replaced without touching the rest of the window. A well-restored original window has decades of life left and will perform better than a cheap modern replacement.
The test is whether the structural members of the outer frame — the pulley stiles and head — are sound. If you can press a screwdriver into them without resistance, or if they are visibly split, twisted, or detached from the masonry, the frame is compromised. Surface rot on sills and rails is repairable; rot that has penetrated the main frame structure is a different matter. We assess this during the free site survey.
Significantly, yes. The biggest source of heat loss in a single-glazed sash window is not the glass — it is the air gaps around the sashes. Professional draught proofing alone reduces heat loss by up to 50% compared to an unserviced window. Adding slimline double glazing on top of draught proofing brings performance close to a modern double-glazed window in a much thinner frame.
Yes — a bespoke timber replacement can match the original profile exactly, including the meeting rail height, sash proportions, glazing bar pattern, and moulding details. This is the only way to maintain the character of a period property and the only option that meets planning requirements on listed and conservation area buildings.
Yes — and this is often the most cost-effective approach. Windows in better condition on upper floors or rear elevations are restored; windows with more severe deterioration on the ground floor or front elevation are replaced. As long as the replacement specification matches the originals, the result is consistent throughout.
A properly restored and maintained timber sash window should last 30–50 years before requiring significant intervention again. Maintenance — inspecting and repainting every 5–7 years — is what keeps the timber in good condition. The original windows in many London properties have been in place since the 1870s and 1880s with nothing more than periodic maintenance.
We offer a free no-obligation site survey across London. We will give you an honest assessment of what is repairable, what is not, and what each option costs — in writing.
Full overhaul of period sash windows — cords, rot, glazing, draught proofing, and painting.
Bespoke like-for-like timber replacements built to match original profiles, with double glazing available.
Full pricing guide for all repair, restoration, and replacement services across London.
Here at Golden Ratio Windows we have built up an excellent reputation in our local area by offering the most comprehensive and expert service in London. From the planning stage to the finished article; we are with you every step of the way, making sure that whatever the task, you are completely satisfied with the end result.
Get a Free SurveyWith so many years working in the trade, we are happy to answer any queries and provide quotes for any work that you are looking to have done. Rest assured that you will be receiving a professional, yet personal service. If you are in need of any work in London or the surrounding areas, get in touch.
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