The effect of a waterproof coating on the long-term hygrothermal performance of a high-rise wall was investigated by combining experimental and numerical approaches. The water vapor permeances (WVP) of the waterproof coating on the brick and mortar masonry were experimentally determined as a function of relative humidity. These performance characteristics for the (WVP) of the waterproof coatings applied on the brick and mortar surface layers were included in the LATENITE version 1.2 hygrothermal model. A series of 1-D and 2-D simulations were performed studying the effects of waterproof coatings on a selected wall system. Additional simulations studied the effect of the existence of cracks. Results indicate that brick-mortar interaction as a system must be included in analysis of the hygrothermal performance of the waterproof coating. Simplifications to 1-D can lead to erroneous results. Rain penetration can be far more important than ambient surface diffusion fluxes and must be included in all hygrothermal analysis. The waterproof coating reduced the yearly average heat flux by 3 % for the city of Vancouver by reducing the latent heat effects of absorbed moisture from wind-driven rain.