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BRE requires the Average Daylight Factor (ADF) to be equal to or greater than 2% for kitchens and equal to or greater than 1.5% for living/dining rooms and home offices. If the ADF is lower than these levels, natural daylighting would not be effective in illuminating the internal space and artificial light would be in use for the majority of the day.

A good indicator that the ADF will be achieved is if the ratio of total window surface area (m2) to the area of the room floor (m2) is 1:10. As the distance from the window increases, the ADF decreases, and therefore limiting the depth of the room is also advised. Deciding where to place the kitchen is important, as 80% of the working plane needs to receive direct light from the sky.

Based on our experience the ADF is a realistic measure. In practice rooms built with an ADF less than the required levels do seem dark. The key is to ensure that the design process co-ordinates the floor plans with external elevations.