108
6.5 Atria
6.5 Atria
In buildings with deeper floorplates or where a high quality of natural light is a design priority, an atrium is an excellent way of increasing the amount of daylight that enters a building. The implementation of an atrium effectively cuts an occupants maximum distance to daylight in half and allows h
Attached
for a higher and more even level of daylighting
l
throughout the space.
w
The best way to quantify the daylighting performance of an atrium is by measuring
Fig. 21 - Atrium Measurements
its Daylight Factor (DF). The Daylight Factor describes the ratio of outside illuminance over inside illuminance, usually expressed as a
Linear
PAR =
w l
percentage. The higher the DF, the more natural light is available in the atrium. The Daylight Factor is affected by the geometry of the atrium, as well as its roof form and the reflectivity of its materials.
SAR =
h w
Plan Aspect Ratio (PAR) The most efficient shape for the plan of an atrium is a circle. In atria with non-circular plans, the PAR can be used to measure the effectiveness
Enclosed
WI =
h x (l + w) 2xlxw
of the space’s geometry. The PAR is equal to the atrium’s width divided by its length. An atrium with a PAR closer to 1 (square) will have better dayighting performance than one with a PAR closer to 0 (linear).
Semi-Enclosed Fig. 20 - Atrium Types
Section Aspect Ratio (SAR) The SAR measures the ratio of an atrium’s height to its width. A low SAR indicates a shallow atrium and a relatively high Daylight Factor.