This paper describes the calculation methods for estimating building surface concentration profiles when point sources are located in the cavity regions of an isolated high-rise building or twin high-rise buildings. The proposed methods use a decay index of vertical concentration profiles as substitutes for diffusion widths based upon Gaussian plume concepts. The index was derived from the experimental results that the vertical concentration profiles were inversely proportional to the power of the distance between point sources and sampling ports on the building surfaces. The empirical formulas could predict the vertical profiles of building surface concentrations with a mean prediction error of 21% for the twin high-rise buildings and 29% for the isolated high-rise building. The prediction accuracy became worse when the location of maximum concentrations could not be estimated well using the streamlines to the downwind building measured by a split-film probe of anemometers.