Steel window refurbishment vs replacement: What Crittall can do 

• 10 November 2025
• News

The iconic steel window, beloved of the early 20th century Modernist era, has established itself firmly in the ranks of ‘design classic’, and as such, rightly gets recognition for its slim frames, elegant design details and enduring strength.

However, time doesn’t stand still and the ravages of the decades, including corrosion, can affect an older steel window’s performance, particularly if it has original single glazing. A question we’re often asked at Crittall Windows is: “Should steel window refurbishment preserve what is already in place, or is a full replacement window scheme the better option?”

This guide sets out what the refurbishment process actually involves, how to recognise the signs that action is needed, what makes a listed or heritage building a special case, and how to decide with confidence which route is right for your project.

Assessing existing windows

The quick answer is that there’s no single rule. Every project begins with careful consideration of the condition of the existing window frames and the architectural significance of the property. Crittall surveyors examine the steel sections, opening mechanisms, glass types and any signs of severe corrosion or distortion. Some existing windows need only targeted repairs. Others have reached a poor condition where failure to act creates an adverse effect on the building fabric.

When refurbishment is viable it is usually the most sympathetic route. Window refurbishment preserves original windows that contribute to the character of the building while improving function. Necessary repairs might include removing corrosion, treating metal frames, renewing glazing putty, installing new glass with better thermal insulation and upgrading weather seals. These actions reduce heat loss and draughts without changing the appearance of the listed building. The result strengthens the character of the building and respects the guidance of Historic England regarding buildings of special interest.

Signs your steel windows may need attention

Not every problem is immediately visible. The following are the most common indicators that a professional assessment is warranted:

• Surface rust or pitting on the steel frame, particularly around joints and the base of the frame where water collects
• Draughts or condensation between panes, indicating failed glazing putty or deteriorated weather seals
• Stiff or seized opening lights caused by paint build-up, distortion, or corroded hinges and stays
• Visible daylight around the frame when the window is closed, pointing to gaps in the weather seal
• Cracked or loose glazing putty, which allows water ingress and accelerates corrosion of the surrounding steel

Identifying these issues early almost always makes refurbishment the viable path. Left unaddressed, surface corrosion deepens into structural corrosion, which narrows the options considerably.

When replacement is the better way forward

Refurbishment is not always possible. Some single glazing, combined with heavily corroded metal windows and the absence of weatherseals, needs a more robust solution. In these situations, new steel windows are engineered to replicate existing window frames but with far superior thermal efficiency and air tightness. Double glazing incorporated into slender steel window sections is the most noticeable improvement. Modern manufacturing also provides greater durability so the building is protected well into the future.

There are strong performance reasons to consider replacement. Older metal frames rarely come close to current expectations for thermal efficiency or acoustic comfort. Introducing new panes of glass with insulated units, improved weather seals and technically advanced steel sections makes a clear and lasting difference. Tenants and homeowners notice a warmer, quieter and more comfortable interior. Estates and commercial buildings also gain long term asset value. Where building consent is required Crittall works closely with architects and planning authorities to ensure full compliance.

The steel window refurbishment process: what to expect

For those unfamiliar with what a professional refurbishment programme involves, it is worth understanding the typical sequence of work. While every project differs according to the condition of the frames and the requirements of the building, most steel window refurbishment programmes follow a consistent structure.

1. Initial survey. A Crittall surveyor inspects every frame on site, recording the condition of the steel sections, ironmongery, glazing and seals. This produces a clear schedule of works and establishes whether refurbishment or replacement is recommended for each elevation or window group.
2. Preparation and corrosion treatment. Existing paint is carefully removed. Any corrosion is mechanically cleaned back to bare, sound metal. The steel is then treated with a specialist primer formulated for use on hot-rolled steel sections, which inhibits future oxidisation.
3. Frame repairs. Damaged or distorted sections are repaired or replaced in kind. Hinges, stays, handles and coupling fixings are refurbished or substituted with matching ironmongery to preserve the original appearance.
4. Re-glazing. Old single glazing and failed putty are removed. Depending on the project specification and planning requirements, replacement glass may be single glazing in a heritage-matched profile, or slim-profile double glazing that improves thermal performance while maintaining the original sightlines.
5. Weather sealing and finishing. New weather seals are fitted throughout. The frames are repainted to the required specification — typically a high-build polyurethane or powder-coat system — in the original or approved colour.
6. Final inspection and sign-off. Completed windows are tested for correct opening, closing, and weather performance. On listed buildings, this stage may include a review by the appointed conservation officer or architect.

Steel window refurbishment in listed buildings and conservation areas

A significant proportion of the UK’s steel-framed windows sit within listed buildings or conservation areas, where planning policy shapes what can and cannot be done. Local planning authorities and Historic England generally favour retaining original fabric wherever possible, which means a well-executed refurbishment is frequently the preferred — and sometimes the only permitted — course of action.

Where replacement is necessary or sought, new steel windows must typically replicate the original profile, section depth, sightline dimensions and opening configuration precisely. Crittall’s manufacturing heritage gives a particular advantage here: our steel sections have been used in landmark buildings across the country since the late 19th century, and our technical team understands the profile requirements needed to satisfy both conservation officers and planning inspectors.

It is always advisable to engage with the local authority at the pre-application stage before committing to either route. Crittall can support this process by providing technical drawings, section profiles and performance data to accompany a listed building consent or planning application.

Projects across the country demonstrate how both approaches can succeed. Crittall Windows returned to Adelaide House in London to replace the steel windows it originally manufactured and fitted in 1925. The Grade II Listed building, located on the north bank of the Thames near London Bridge, required new windows that preserved its historic aesthetic while meeting strict planning requirements. Crittall selected double glazed Corporate® W20 EVO windows with 20mm insulated glass, which replicate the original sightlines and hardware but offer modern thermal performance. These new steel windows complement the extensive refurbishment of the riverside office block, combining century-old style with contemporary functionality.

The architectural significance of a property deserves expert attention. Crittall has been manufacturing steel frames since 1849 and continues to support those responsible for preserving the United Kingdom’s built environment. The team can refurbish original frames or design new steel windows that match the original appearance. Every decision aims to protect what makes a building special, while ensuring it meets the standards expected today.

Frequently asked questions

Can Crittall windows always be refurbished?

In most cases, yes. The hot-rolled steel sections used in Crittall manufacturing are exceptionally durable, and surface corrosion rarely extends to the point where the structural integrity of the frame is compromised. A site survey will confirm whether refurbishment is viable, and in many cases the answer is that a targeted programme of repair and re-glazing will restore full performance for several decades.

How long does steel window refurbishment take?

Timescales depend on the scale of the project and the condition of the frames. A modest residential scheme might be completed within a few days. A larger commercial or heritage project involving multiple elevations will typically be phased over several weeks to minimise disruption to occupants. Crittall provides a full programme schedule at the outset so that building owners, facilities managers and architects can plan accordingly.

Is planning permission required for steel window refurbishment?

Like-for-like repair work, including re-glazing and repainting in the same colour, generally does not require planning permission. However, any change to the profile, opening configuration or glass specification on a listed building or within a conservation area will normally require listed building consent and/or planning approval. Crittall’s team can advise on the likely planning position for your project before works begin.

What is the difference between in-situ and ex-situ refurbishment?

In-situ refurbishment means the windows are treated, repaired and reglazed while remaining in the building’s aperture. This is the preferred approach for most projects as it minimises disruption and avoids the need to board up openings. Ex-situ refurbishment involves removing the frames entirely, transporting them to a workshop for shot-blasting and full restoration, and then reinstating them. This approach is sometimes necessary where corrosion is severe or where access constraints prevent adequate preparation on site.

• For more information on refurbishing and/or replacing steel windows, contact us here.