THE CRITTAL WINDOWS DYLEMMA: HERITAGE VS THERMAL EFFICIENCY

Crittall windows are an iconic feature of British architectural history, celebrated for their slender profiles and industrial elegance. However, many original installations are single-glazed, making them notoriously inefficient at retaining heat or excluding the cold.

In one of our current London projects, our client attempted to replace her original windows with a more modern, thermally efficient system. The local planning authority refused the proposal, a decision that has become increasingly common across London boroughs.

Planners frequently resist individual window upgrades, often advocating for comprehensive building-wide improvements instead. This is not always a viable or reasonable expectation for a single leaseholder or homeowner. When alternatives are sought, clients are typically presented with the narrow option of a "like-for-like" replacement.

If you find yourself in this position, there are three critical factors to consider:

1. A True "Like-for-Like" Replacement Is Often Impossible

It is a misconception that a new window can perfectly replicate an antique one. Crittall has evolved its manufacturing and detailing significantly over the decades; therefore, a 2026 Crittall window will not be an identical match for an older version.

Current manufacturing standards and minimum height restrictions are more stringent than in the past. Furthermore, certain historical configurations, such as the pivoting mechanisms found in our current project, are no longer in production. Crucially, modern double-glazed units require bulkier frames to support the additional weight and thickness, which inevitably alters the visual proportions of the window.

2. Full Replacement May Not Be Necessary

In specific instances, original single-glazed Crittall frames can be refurbished rather than replaced. It is sometimes possible to reglaze existing frames with slim-profile double-glazed units (for example: a 4mm glass pane, a 6mm gas-filled cavity, and 4mm e-glass).

In addition to reglazing, original mechanisms can often be serviced, and weather seals can be reinstated or replaced to improve performance. This approach preserves the original architectural fabric while enhancing thermal comfort.

3. The Necessity of Expert Inspection

Because there are numerous generations of Crittall products, there is no "one size fits all" solution. Not every steel panel can be safely dismantled or successfully upgraded to house double glazing.

Before committing to a course of action, an expert should inspect each window in detail. They will determine if the existing frame can support the weight of new glass and whether the structural integrity allows for a meaningful upgrade.

Navigating Heritage Requirements in London

Preserving the soul of a building while meeting modern energy standards requires a sophisticated architectural approach. At our studio, we navigate these complexities by blending technical expertise with a respect for historical context.

Are you currently managing a renovation involving heritage windows? We invite you to contact our studio to discuss how we can help you navigate the planning process and technical requirements.