An experimental study was conducted to answer questions about the thermal effects of roof reflectivity on the neighbouring built environment. Temperatures were recorded at the surface of black ethylene propylene diene monomer (EPDM) and white thermoplastic polyolefin (TPO) membrane overlay areas; in the air and at electrical metallic tubing (EMT) above them; and at opaque and glazed wall surfaces adjacent to them. The surface of the EPDM roof was significantly hotter than the TPO roof by 36°C and 26°C on two test dates. Air temperatures were 2°C higher above EPDM versus TPO up to 14 cm, with no significant differences above this height. Temperatures were 2°C higher at EMT above the TPO surface than above the EPDM. A precast concrete panel wall was 3°C to 5°C warmer adjacent to TPO versus EPDM. Exterior glazing surface temperatures were 2°C warmer adjacent to TPO versus EPDM.