More recent UK climatic data for use in the design of naturally ventilated buildings show that passive stack ventilation alone is unlikely to maintain summertime comfort in a new University College London building within the London city heat island. A stack ventilation strategy developed by the design team was evolved by the introduction of passive downdraught cooling (PDC). PDC enables cooled air to be distributed throughout the building without fan assistance. The underlying principles of the technique were explored using computational and physical models. The architectural integration and seasonal control modes are described. Predicted performance of PDC is compared with actual measurements. (C) 2009 Elsevier Ltd. All rights reserved.