PRODUCT ANNOUNCEMENT: the first sash windows to reach 1.2 u-value

Roseview Windows are delighted to announce the launch of ThermoVFlex technology, making us the first and only timber-alternative sash window company to reach a u-value of 1.2 w/m2K without the need for specialist glazing. Find out more about this ground-breaking new development below.


Roseview now offer sash windows with significantly reduced u-values. Our class-leading Heritage and Ultimate Rose sash windows are available with a certified U-value of 1.2 W/m2K without the use of specialist glass such as triple or vacuum glazing.

This advance uses our new ThermoVFlex system, which is based upon patented technology developed by REHAU. ThermoVFlex centres on improving the window’s u-value through profile enhancements, rather than relying on specialised glass.

Managing director Richard Burrells explains more:

“Until now the only way to reduce the u-value on sash windows below 1.4 W/m2K was with triple or vacuum glazing. Both options have serious problems, including cost, weight and practicality. For instance, most sash windows include astragal bars, which do not work well with triple or vacuum glazing.

“ThermoVFlex allows us to manufacture a Heritage or Ultimate Rose sash window with a 1.2 u-value, while using the same IGUs that previously gave us 1.4. It costs much less than triple glazing and vacuum units and doesn’t impose restrictions on the use of safety glass, patterns or astragal bars.”

“This is a major advance in sash window technology.” Richard continues. “While the Future Homes Standard is maintaining current U-value requirements, finding economically viable ways of improving energy efficiency remains important. For new-builds in particular, this gives customers more room to manoeuvre with their limiting values.

“ThermoVFlex costs much less than triple glazing and vacuum units and doesn’t impose restrictions on the use of safety glass, patterns or astragal bars.”

“Roseview has a long history of innovation, pushing back the boundaries of what is technically and visually possible with sash windows. This is simply a continuation of that, made possible by our close partnership with REHAU.”  Richard concludes.

Partnership with REHAU

Commenting on the launch, Russell Hand, Head of Product Management and Technical at REHAU Window Solutions UK said:

“REHAU have been setting the standards in window development for over 30 years. Our latest development is a patented technology that can reduce the U-value of our windows without the need for specialist glazing. It’s a significant step which is particularly relevant for sash windows and so it made perfect sense to work with long-standing REHAU customer Roseview to launch this exciting new technology.”

ThermoVFlex is available as an option on our Ultimate Rose and Heritage Rose sash windows, from the end of February 2024. Get in touch for more information about ThermoVFlex or any of Roseview’s sash windows.



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