The real or effective thermal capacitance of buildings quantifies the energy stored within and differs considerably from the apparent thermal capacitance, which results by adding distributed specific heats of building elements into a lumped value. In the present study, a method is developed for analyzing the total effective capacitance into components concerning the building envelope or parts of it (e.g. ceiling, floor, etc.), the interior partitions, the furnishings, etc. The developed procedure is based on a finite-difference solution of a set of differential equations describing the transient heat conduction in all elements of a building. Applications are made to 21 types of buildings with 15 and 10 wall and roof compositions, respectively, and floor area from 50m² to 2500m². For example, it is found that for typical fully-insulated, one-storey, detached houses, the envelope, interior partitions and furnishings effective heat capacitances are 78.1%, 14.5% and 7.4%, respectively, of the total effective thermal capacitance. Also, a correlation is developed, which links the effective to the easily-calculated apparent thermal capacitance of buildings.