Relationship between Window-to-Floor Area Ratio and Single-Point Daylight Factor in Varied Residential Rooms in Malaysia

Abstract

Objectives: Daylight studies on buildings are key aspects of environmental analysis, and can be conducted during early stages of design to ensure environmentally responsive building design. The Malaysian Uniform Building By-law states that rooms should be provided with natural lighting and natural ventilation through one or more windows with a total area of not less than 10% of the clear floor area. This requirement is depicted by the window-to-floor area ratio (WFR). Methods: The by-law is further investigated by determining the relationship between WFR and daylight levels in terms of percentage daylight factor (%DF). The WFR minimum stated in the by-law is assessed using two tests: (1) Determining whether a WFR less than 10% is indeed inadequate for lighting purposes, and (2) Whether a maximum WFR should be imposed to avoid over-lit spaces. Research was conducted in a condominium unit with varied room designs and WFR. Natural illumination data were collected at midpoints of four different rooms for comparison with simultaneous outdoor illumination over a span of several days to obtain average %DF values. Findings: A strong direct relationship exists between WFR and natural illumination levels (in terms of %DF). In a local context, a WFR less than 10% was found to provide sufficient daylight levels in typical rooms, whereas a WFR more than 25% could cause rooms to be over-lit. Keywords: Daylight Factor (%DF), Uniform Building By-Law (UBBL), Window-to-Floor Ratio (WFR), Window-to-Wall Ratio (WWR)