Multizone airflow modelling is used for IAQ analysis as well as evaluation of cooling potential in buildings. A detailed evaluation of the wind pressure distribution on the envelope of a building is important for multizone: airflow modelling. There are a number of variables affecting the pressure distribution around a building due to natural wind. Wall-averaged values of Cp usually do not match the accuracy required. for multizone: airflow models. In order to obtain a more detailed evaluation, taking the Cp distribution on the envelope of buildings into account, a numerical model (CPCALC+) based on a parametrical analysis of wind tunnel test results was developed at the Lawrence Berkeley Laboratory, University of California, for the COMIS multizone airflow calculation program and upgraded whit the CECDGXII PASCOOL programme. CPCALC+ calculates Cp values at any position of a surface element on the envelope of a rectangular shaped build with flat or tilted roof for given conditions of terrain roughness, density of surrounding buildngs, shape ratios, and wind direction This paper describes the parametrical approach used to analyse the reference Cp data as well as the algorithms included. in the calculation model. The variation of Cp with respect to reference boundary condition was analysed. in relation to several parameters: wind velocity profile exponent, plan arca density, relative building height, frontal and side aspect ratios, wind ncidence angle, roof tilt angle fcade element positioning co-ordinates. Some of the relevant curve-fitting function are shown. A flowchart of the program is also presented.