'The intention of the Calculation Techniques Guide is to provide researchers and designers with detailed background to air infiltration modelling and to give step-by-step guidance on the application of modelling techniques in design. Particular emphasis is placed on providing specific guidelines on the calculation of steady-state air infiltration and on air change rates in industrial, commercial and domestic buildings. Associated calculations include the determination of infiltration heating and cooling loads, air flow and internal pressure distribution, the prediction of pollutant concentrations in buildings and an analysis of cost effective ventilation strategies. In addition to providing these guidelines, the rationale behind each calculation technique is described in full. Since the approach to ventilation strategy varies considerably on a national basis (largely as a result of climatic differences), the varying needs of each country are also discussed.'