Daylighting of large span buildings – research findings A research project commissioned by the Association from The Institute of Energy and Sustainable Development at De Montfort University concludes that adequate daylight can be provided through rooflights without creating the risk of solar overheating. Download Research Document Part L raises a question Using sophisticated computerised modelling the research investigates issues raised in Building Regulations Approved Document Part L2 which says that a rooflight area must be large enough to provide sufficient natural daylight, but it must not create the risk of solar overheating. It states that “special care needs to be given to confirm that levels of daylight are adequate” if the rooflights area is less than 20%, but, also, that one way of avoiding risk of solar overheating is to limit the rooflight area to 12 per cent. The computerised modelling also established solar gain from rooflights inside large span buildings, defining the maximum area of rooflights that can be fitted while avoiding risk of solar overheating. This varies with internal gains in the building. The research concludes that the minimum rooflights area required for ‘adequate’ natural daylighting are lower than the maximum limits to avoid solar overheating, offering a range of rooflights that will meet both requirements.