The resistance of bituminous built-up roofing membranes to thermally induced forces is considered in terms of their strength properties such as breaking load in tension, modulus of elongation and apparent linear thermal expansion coefficient.The development of a Thermal-Shock Resistance Factor is described and values are given for three bituminous built-up membranes at temperatures of - 30F (-34.4C), 0F (-17.8C), 30F (-1.1C) and 73F (22.8C).The apparent relation between the values obtained in the laboratory and the observed performance of roofing membranes in service is considered.The utilization of the Thermal-Shock Resistance Factor in the reduction of potential failures of bituminous built-up roofing membranes in service from thermally induced forces is also discussed.(Author).

The values of breaking load, elongation and thermal expansion of nine bituminous built-up membranes prepared by roofing contractors under field conditions and by technicians in the laboratory were measured at sub-freezing temperatures.The data indicated that the field-prepared specimens agreed favorably with laboratory-prepared specimens, although the samples from the field frequently reflected higher values for thermal-shock resistance than did their laboratory-prepared counterparts.The higher values were attributed to the smaller amounts of bitumen used between the plies of the field specimens.The results appeared to support the validity of the application of the 'strength-thickness rule' to bituminous built-up membranes.(Author).