The suitability of night ventilation for cooling offices in moderate climates such as that of the UK is first assessed by presenting plots of summer weather data on the bioclimatic chart for three locations within the country. These indicate that most of the external weather conditions lie within the thermal mass and ventilation effectiveness areas of the charts. To confirm this, thermal simulations of a typical office module under a variety of internal conditions and summer weather data were performed. Predictions have shown that internal temperatures can be maintained below the external values for solar and internal gains of up to about 50 W/m(2) of conditioned floor area. Field measurements in a refurbished office have confirmed that temperatures in night-ventilated spaces are generally lower during the following day, especially during the early hours of the working day. Finally, the development of a pre-design tool in the context of IEA Annex 28 on ＇Low-Energy Cooling Systems＇ is discussed. The main aim of the tool is to increase the awareness of designers for the energy benefits and the range of parameters for the application of night ventilation as the first means of cooling, so that the need for artificial cooling is minimised or avoided altogether.