Building Research studies show that overheating because of excessive solar heat gains can be troublesome in buildings of lightweight construction with large areas of glazing. The work being done at the Building Research Station provides the data for calculation of peak temperatures resulting from solar heat gain. Attention is given to window size and orientation, ventilation, and the effects of sun-controls. Graphs aid in computing peak temperatures as a function of unshaded window size for multi-story blocks of offices. These graphs determine the maximum permissible areas of glass to be used in offices when heat gain by solar radiation is part of the design criteria. (TC)