What is fenestration ratio and how does it affect daylight and heat gain?

• A. The ratio of door area to wall area; larger ratio increases daylight and reduces glare
• B. The ratio of window area to wall area; larger ratio increases daylight but may raise heat gains; requires shading strategies.
• C. The ratio of interior doors to exterior doors; larger ratio improves ventilation
• D. The ratio of roof openings to wall openings; larger ratio reduces glare

Answer: (B)

Fenestration ratio is the proportion of window area to the total wall area. When this ratio is larger, more daylight can enter a space, improving visual comfort and reducing the need for artificial lighting. But more window area also means more solar heat gain, which can raise cooling loads unless shading and glazing strategies are used. So the best approach is to balance daylight benefits with thermal performance by selecting appropriate glazing, using shading devices (like overhangs or louvers), and aligning window placement with the climate and orientation. In contrast, other ratios that focus on doors or roof openings don’t describe how daylight and heat move through the building envelope, so they don’t capture this important trade-off between light and thermal gain.