That would depend on the operational requirements for that building and the specification of the rooflight because there are several options to suit different requirements. The provision of natural daylight rather than artificial light has been demonstrated to deliver more energy savings than can now be achieved through increasing insulation levels.
Studies have demonstrated that the optimum rooflight area is usually in the region of 12 to 18%. At higher rooflight levels, consideration should be given to the risk of solar over-heating at the hottest times of the year, and the ventilation strategy for the building.
