Air leaks into a building through various openings and cracks in the building envelope. This leakage affects indoor air quality, human comfort and, primarily, building energy consumption. Several experimental studies have estimated this energy impact to exceed 40% of the heating and cooling costs in buildings. Current methods for evaluating air leakage range from simple air change methods to multizone coupled methods. These vary between being overly simplified to complex sets of equations that utilize hard-to-obtain, often assumed, factors and coefficients. Some CFD simulations have also been attempted. They only consider a small portion of 2-D wall sections with a single predefined air flow path. A modeling methodology is developed in this work that represents a roadmap for performing full 3-D envelope multiphysics hygrothermal simulations for air leakage in buildings. The methodology realistically depicts the various cracks common in an envelope in terms of shape, location, and quantity. It also accounts for the true multiphysics nature of the problem and for various hourly weather variables. The higher accuracy expected with this methodology allows for a more accurate calculation of air leakage heat loading necessary for an efficient building energy design, and for various green and sustainable building design applications. (C) 2013 Elsevier B.V. All rights reserved.