The European standard EN15251 was recently adopted to define acceptable indoor temperatures and light levels as the basis for energy calculation. The provision of comfort is a key concern for building designers. Mechanical cooling is energy intensive. Naturally ventilated (NV) buildings with fewer energy costs cannot control indoor conditions closely. Formally standards have used comfort models which favour close environmental control so NV buildings have been looked on as second-rate. EN15251 allows NV buildings more freedom for environmental variation in line with the findings of comfort theory. This project seeks to use existing information from field surveys to test the limits set by EN15251 for temperature and lighting and to validate its recommendations using existing data and building simulations.