Re-thinking the sash window

Keane Grantham, Marketing Manager at Roseview Windows, explains how thermal performance and practical design is reshaping window specification in commercial and heritage projects.

For a product that has been part of Britain’s architectural language for centuries, the sash window is evolving in response to the demands of modern construction. In today’s commercial market, windows are no longer assessed on appearance alone. Architects and specifiers are balancing aesthetic intent with long-term durability, energy performance, maintenance expectations and the practical realities of delivering large or phased schemes, often under tight commercial pressures.

That shift in expectation has been shaping product development at Roseview Windows for some time. Best known for its uPVC sash windows, the business has a longer and more varied history than many in the sector might realise, and its renewed focus on commercial and heritage-led projects reflects a broader change in how sash windows are being specified. 

Rather than being viewed as a niche or specialist element, the sash window is increasingly being treated as a scalable, credible solution that can sit comfortably within large developments, conservation settings and mixed-use schemes.

Roseview’s origins lie firmly in the replacement market, with its early work focused on addressing the limitations of traditional timber windows in social and public sector housing. One of the company’s formative moments came through a collaboration with the Peabody Trust, as Keane Grantham, Marketing Manager at Roseview Windows, explains.

“We were approached to replace windows that were failing as timber, and that brief really shaped the direction of the business,” he says. “From the beginning, the focus was on creating a product that could act as a genuine timber alternative, not just visually, but in terms of performance and longevity too.”

Since switching fully into manufacturing in 1985, the business has steadily expanded its offer, moving from a single uPVC sash window into a carefully tiered range designed to meet different project needs. Today, Roseview positions itself not simply as a window supplier, but as a specification partner, offering a consistent design and performance across a wide range of projects.

“From a commercial standpoint, many projects are budget-led,” Keane says. “Developers want the most cost-effective solution that still meets performance requirements and looks right for the scheme. That’s why we’ve designed our whole range so that even our lower and mid-range products can compete well on U-values and aesthetics.”

Across the range, all Roseview’s sash windows are A-rated, with U-values as low as 1.4 available on entry-level systems, dropping further to 1.2 on mid-range and premium options. This allows specifiers to align with the anticipated requirements of the Future Homes and Building Standard while still having multiple design options.

Why design still matters at scale

While compliance and cost remain central to commercial decision-making, design quality continues to play a significant role, particularly on developments that aim to establish a strong sense of place from the outset.

“Design matters more than people sometimes expect on commercial projects,” says Keane. “Even when budgets are tight, there’s still a strong desire to create developments that feel established, especially on newbuild sites that look to reflect older architectural styles.”

In response, Roseview has placed renewed emphasis on heritage detailing, particularly within its higher-end sash window systems such as Ultimate Rose. This includes slimmer sightlines, deeper sills and an expanding choice of sash horns, each intended to reflect specific architectural periods rather than acting as decorative afterthoughts.

“We offer a range of sash horns, including dolphin, seahorse, no-horn and our newer Emperor horn,” Keane explains. “They’re design choices that help the window suit the time period of the building and the local area, whether that’s Georgian, Victorian or Edwardian.”

The recently introduced Emperor horn (pictured), which combines a more pronounced definition with balanced curves, was developed to replicate traditional joinery more closely, giving architects greater freedom to match historic proportions on both newbuild and replacement projects.

Replicating timber

One of the ongoing challenges in sash window design is closing the visual gap between traditional timber construction and modern materials. According to Keane, achieving this requires a holistic approach rather than a collection of surface-level features.

“Our approach has always been about designing the whole window as a complete package,” he says. “We talk about the window being more than the sum of its parts, because all the elements are designed to work together to create the slim, seamless appearance you would expect from an original timber sash window.”

On Roseview’s premium systems, this includes joinery-style mechanical joints and seamless mid-rails and sash horns, which remove the visible lines often associated with uPVC windows.

Additional features, such as removable staff beads and optional chamber covers, further support the timber-like appearance of the windows while retaining modern functionality, allowing for easier cleaning and maintenance without compromising on the aesthetic finish.

Thermal performance

Energy efficiency remains an important factor in winning commercial specifications, though sash windows bring their own set of challenges due to their inherent design.

“Sash windows aren’t compression-sealed by nature,” Keane explains. “They’re designed to allow airflow, which historically helped manage ventilation and reduce issues like damp and mould. That means they’ll never reach Passivhaus-level U-values, but they can still perform extremely well.”

To enhance thermal performance without altering how the window operates, Roseview developed its ThermoVFlex technology, which uses an internal foil to improve insulation.

“We can achieve U-values down to 1.2 by combining glazing options with our ThermoVFlex system,” says Keane. “That gives specifiers flexibility. On platforms like NBS, where our products are available, specifiers can select the target U-value first and then configure the window to suit the design they want.”

This approach allows different performance levels to be specified across a development while maintaining a consistent aesthetic.

A credible timber alternative

Despite advances in timber treatment, maintenance remains a concern for many commercial clients, particularly on large-scale or publicly funded developments.

“Timber has improved a lot, but it’s still a material that needs ongoing maintenance,” Keane says. “From a commercial perspective that can be a real drawback, especially when you’re managing a project with hundreds or even thousands of units.”

Roseview’s uPVC sash windows are designed to address that concern directly. Stainless steel spiral balances replace traditional cords and pulleys, reducing wear over time and improving long-term reliability.

“Our windows are designed to last,” Keane adds. “They come with a 10-year manufacturer’s warranty, but we regularly see installations that are still performing after 30 years, including in coastal locations and colder northern environments.”

The recyclability of uPVC also plays a role, with Roseview working with profile suppliers who operate closed-loop recycling systems, supporting wider sustainability objectives without introducing additional maintenance burdens.

Colour flexibility

Colour choice and finish are also areas where modern materials offer a clear advantage. While timber can be painted or stained, changing colour schemes over time is labour-intensive and disruptive.

“All our profiles are foiled in a wide range of textured finishes,” says Keane. “That gives designers an almost unlimited colour choice, and if a project needs something outside the standard range, we can spray or apply specialist foils in-house.”

This level of flexibility supports both contemporary and heritage aesthetics, allowing windows to complement surrounding materials and architectural context without being restricted to stock finishes.

Large-scale delivery in practice

Roseview’s approach has been tested at scale on projects such as Welborne Village, Hampshire, where sash windows were specified across thousands of homes.

“The project was chosen from a huge range of materials and window types,” Keane explains. “What stood out for the client was the combination of slim sightlines and authentic sash detailing, alongside the long-term benefits of a maintenance-free material.”

For developments of this size, consistency across phases is essential.

“If you’re building an entire village, you don’t want the first homes needing major maintenance while the last ones are still under construction,” Keane says.

Supporting modern specification

As digital platforms increasingly shape how products are researched and specified, Roseview has expanded its presence across a range of tools used by commercial specification teams. 

“We know architects and QS teams want clear information and realistic pricing early on,” says Keane. “That’s why we’re active on NBS and platforms like Tommy Trinder and BM Touch, offering live pricing and configurable options.”

While the commercial windows sector continues to evolve, Roseview’s focus remains on refining its core offer rather than chasing short-term trends.

“We’re continuing to innovate within the sash window space and sticking to what we’re good at,” Keane says. “That includes developing the aesthetics, performance and regulatory compliance of our main range, supporting heritage projects, and offering secondary glazing solutions where replacement isn’t possible.”

With increasing attention on improving existing housing stock as well as delivering new homes, that balance between performance, appearance and long-term practicality looks set to remain central to commercial window specification in the years ahead.

www.roseview.co.uk