This work focuses on air-tightness and air-infiltration of industrial buildings of light steel structure. Extensive measurements of leakages in typical building components and connections in industrial buildings were carried out in a specially built air-tightness test stand. Typical leakages were detected and reduced. Measurements of the volumetric flow through single leakages were compared to results of blower door tests of large industrial buildings. The measurement data gained in the test stand was further used for transient air-flow network simulations coupled with the software TRNSYS. Based on a database of more than 4000 industrial buildings, 28 typical building shapes were defined and different inside temperature profiles were assumed. Each building was modeled and simulated with up to 84 defined cracks. The cracks were based on the measurements in the test stand and represent a typical leakage distribution of industrial steel buildings. In total 140 different simulations were used to create a new infiltration model. This model provides monthly coefficients that consider the seasonal cycle during the year as well as the building height, size and inside temperature. This new model is easy to implement in energy balance calculations and helps determining energy demands even with steady state methods with greater precision. (C) 2014 Elsevier B.V. All rights reserved.