Air leakage is a crucial factor when assessing the hygrothermal performance of wood-frame walls since it can lead to moisture accumulation during the cold season. The seriousness of this prob-lem may change in a warmer climate in the future and hygrothermal simulations are widely used as a tool to predict this effect. However, since 2D models are required for detailed air leakage as-sessment and the high number of input variables leads to having to conduct thousands of simula-tions for a single type of building cladding, downsizing the simulation grid to the lowest number of cells is a crucial task to help ensure reduced computational time. Using a hygrothermal simulation tool, the steps needed to build the smallest 2D grid were explained; as well, convergence and ac-curacy of the results were evaluated and the functional relations between air leakage rate and air permeability of the insulation were clarified. Hygrothermal simulations were performed for wood-frame walls having brick veneer and stucco cladding for three Canadian cities: Whitehorse, Van-couver, and Ottawa. While the air leakage rate has a significant impact on the inner surface of OSB, wind driven rain is the key factor on the outer surface. The performance of stucco cladding is worse than brick in all cases and the future climate may reduce the risk of mould growth on the in-ner surface of OSB in all cities. The results also show that the simulation time can be reduced by 90%, with negligible loss of accuracy, when comparing fine to optimized meshes.