54
EXTERNAL ENVELOPE
Ventilation & indoor comfort In parallel, windows and doors are vital in supporting natural ventilation strategies. Cross ventilation, stack effect, and purge ventilation depend on the thoughtful arrangement of openings within a fl oor plan. Mechanical systems continue to play a role, but low-energy buildings increasingly look to natural or hybrid strategies to reduce reliance on active cooling. Operable windows, roofl ights, and glazed doors provide adaptable solutions for seasonal shifts, enabling designers to respond to both occupant comfort and carbon targets.
Roof windows
Although roof windows may sometimes be perceived as ‘standard’ items, in practice, specifi cation decisions can have signifi cant implications for both performance and long-term maintenance. Architects need to weigh options carefully to ensure they suit the intended use and context of each space. Operation type also has an impact on usability. Centre-pivot windows, for example, are practical where accessibility is straightforward, but top hung or dual function models may be preferable where clear outward views or higher installation
heights are priorities. Where manual reach is limited, electric or solar-powered roof windows support options for remote control or integration into home automation. The number and arrangement of roof windows are another design variable. A single unit can provide valuable daylight and ventilation, but multiple windows in combination can transform interior spaces.
Responding to the unintended consequences of Part O Part O’s simplifi ed calculation method has led to unintended consequences by limiting maximum glazing areas and reducing daylight opportunities. For architects, this creates a tension between compliance and design quality. The key is to prevent overheating without compromising daylight or spatial character. To resolve this, approaches such as external shading systems stack-effect ventilation, and passive design that balances glazing ratios, shading, and ventilation are emerging as practical ways to comply while keeping interiors bright and welcoming.
Richard Williams is senior architectural development manager at Velux
WWW.ARCHITECTSDATAFILE.CO.UK
ADF OCTOBER 2025
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