Thirty years ago, Professor Sue Roaf designed and built a pioneering, low-carbon home using some of the most advanced energy-efficient building components available at the time, including NorDan windows and the first solar panels in Britain. Three decades later, those same windows are still performing flawlessly, and the solar roof is producing 80% of the electricity it did in 1995.
Years before people talked about Net Zero and Passivhaus buildings, Sue Roaf, now Professor Emeritus at Heriot-Watt University and a well-known architect and academic, created what still remains one of the most energy-efficient and climate-safe houses in the country.
In 1995, driven by a recognition of a warming planet and decades of studying traditional desert technologies in Iraq and Iran, Professor Roaf set out new strategies for designing future-facing houses, testing and including them in her six-bedroom Oxford Ecohouse.
At the heart of her Ecohouse was the idea that buildings should operate for as much of the year as possible on clean, free, and locally sourced renewable energy.
This means connecting the internal climates of the building with the local micro-climates around the home, not least through sensible and useful window design.
Amid a growing focus on energy efficiency and carbon emissions, the Oxford Ecohouse in 2023 emitted just 2.25 kg CO₂ and used only 12 kWh of imported energy per square metre annually, a figure well below typical domestic targets.
But there is more to making a good home than just carbon emissions. An increasingly important requirement is that the building itself, not its equipment, keeps people safely cool in summer and affordably warm in winter.
As detailed in their classic book on Ecohouse Design, Professor Roaf explains how the Oxford house achieved this largely through passive strategies and simple behaviours, like when to open or close windows.
These measures included correct orientation, sensibly sized and shaded windows and high levels of thermal mass in the concrete walls and floors. Thermal mass usefully stores solar gain in winter to keep the house warm at night and retains cool night air in summer to avoid overheating.
A detailed study of the home's carbon impact showed that within approximately 22 years, its low operational energy and maintenance requirements had offset the extra embodied energy used in its initial construction.
However, one of the home's most notable features is its original NorDan windows, which Professor Roaf calls her ‘Rolls Royce’ windows, chosen for their durability and ability to support secure, natural ventilation all year-round.
Inspired by Prof. Roaf’s 1995 vision, NorDan proudly supplied bespoke tilt-and-turn windows at cost price. These striking timber frames flood the home with plenty of natural daylight and enable natural cross-ventilation, keeping it comfortable even during heatwaves and cold spells.
Their unique triple-layer configuration, including double glazing with an unusually large air gap and a single external glazing layer, results in exceptional insulation values and reduces thermal bridging. The external anodised metal outer window provides a durable rain-screen feature protecting the internal softwood windows.
Today, almost three decades later, the original windows remain in perfect working order, with at least another 30 years of expected performance ahead.
The windows are configured for effective summer cooling, using 'night flushing' of heat from the structure. Roaf emphasises the often-overlooked importance of windows that can be safely left open at night or while occupants are away using two secure ventilation strategies:
The first is by positioning small vent windows above and below the French doors that open from both the ground and first floors into the sunspace on the south side of the house. This means that in winter, the sunspace acts as a natural heat pump during the day as warm air enters the house through them on sunny days. On summer nights, cool air is then drawn from this space passing up through the house to be dumped out through the roof windows.
People focus on the light-giving qualities of windows but often forget how they contribute to the seasonal heating and cooling of a house and to the security of its occupants. All the windows in this house are not just light sources but also part of very effective summer, winter and shoulder-season natural ventilation systems.
Sue Roaf
Professor
Secondly, all the windows that lead directly from rooms to the outside are tilt-and-turn design, allowing them to be left securely open both day and night. The dimensions and thickness of these super-windows also make it virtually impossible to break the glass and climb in through them.
This is a climate-safe building. If there’s an extreme heatwave or an extreme cold spell and the grid goes down, you are perfectly safe in the Ecohouse, not least because of the quality and design of its windows.
When combined with other passive design strategies and the pioneering solar roof, the Ecohouse achieves ultra-low running costs. In June 2025, the energy bill (excluding VAT and standing charges) was just £7.14. A clear reminder that investing in whole-life performance pays off in the long run.
This house, when it reaches 50 years old, will probably look just the same as it did when it was built. Its design is intentionally ordinary-looking, neither futuristic without an overly ‘eco'-aesthetic.“NorDan backed the vision from day one — they gave me the windows at cost price because they believed in the idea of living comfortably with virtually no emissions. Thirty years on, that vision has turned into a demonstrated reality.
Since its inception, the house has inspired worldwide interest. Professor Roaf’s book Ecohouse: Design Guide, a practical and influential guide on designing and building sustainable, low-carbon, climate-resilient homes, has been translated into six languages and is now in its 4th edition.
Want to see more of NorDan’s windows in action? Find out about our other landmark UK projects here.
