EXTERNAL ENVELOPE 53 Light, air & effi ciency
Richard Williams of Velux explains why windows are fundamental to the balancing act architects need to perform in order to design the right building fabric.
W
indows and doors are not simply part of a building’s envelope; they shape how spaces perform,
contribute to fabric effi ciency, and help deliver low-carbon, healthy environments for occupants. Designing openings within the building fabric has always required architects to balance aesthetics, structure, and performance. Today, that balance has become increasingly complex as regulation, sustainability targets, and occupant expectations converge. Doors and windows play a critical role in defi ning thermal performance, daylighting, ventilation, and wellbeing, making them integral rather than peripheral to design intent.
The conversation around doors and windows is no longer limited to material selection or frame detail. These components are now part of a broader system in which energy effi ciency and carbon reduction are paramount. With Building Regulations tightening, the performance of glazing and frames contributes directly to whole building targets for heat loss, overheating mitigation, and operational energy use. In practice, this means architects must treat the design of openings not in isolation, but as interdependent with insulation strategies, airtightness measures, and services integration.
Access to natural light remains one of the most powerful benefi ts that well considered glazing can deliver. Research consistently highlights the role of daylight in improving occupant health, productivity, and mood. For designers, window and roofl ight positioning determines how light is distributed within a space, whether the aim is to minimise artifi cial lighting demand or to create a specifi c spatial character. The proportions and placement of openings can transform small areas into generous, uplifting environments while maintaining energy performance.
Studies show that roof windows can deliver up to two times more daylight than facade windows of a comparable size, because of the direct angle of overhead
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light. This is especially relevant for deep plan or single-storey spaces where wall glazing alone may not achieve suffi cient penetration. Flat roof windows extend this opportunity further, and can offer up to three times more daylight as they introduce it into areas where conventional windows cannot be used at all. The proportions and placement of these openings can transform small areas into generous, uplifting environments while still supporting energy performance goals.
One example of this approach is the use of roof windows, which are frequently specifi ed to introduce daylight deep into plan forms or retrofi t projects. By opening up previously underlit spaces, such solutions can signifi cantly improve spatial quality while supporting low-energy lighting strategies.
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Architects need to weigh options carefully to ensure they suit the intended use and context of each space
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