Shading by neighbouring buildings and trees impacts the energy requirement of a building by reducing the amount of radiant energy absorbed and stored by its thermal mass. This study intends to quantify the magnitude of the effect of site shading on the energy requirement of residential buildings in Canada using a representative two-storey detached house. Site shading effects of neighbouring buildings and trees on annual heating and cooling energy requirements are evaluated using a building energy simulation program. The effects of the orientation, distance and size of the neighbouring object on heating and cooling energy requirement are investigated for four major cities (Halifax, Toronto, Calgary, Vancouver) representing the major climatic regions in Canada (Atlantic, Central, Prairies, Pacific). It is found that the annual heating and cooling energy requirement of a house in Canada may be affected by as much as 10% and 90%, respectively, by the existence as well as the orientation, size and distance of a neighbouring obstruction. Therefore, it is recommended that in building energy simulation studies, external shading should be given due consideration. (C) 2011 Elsevier B.V. All rights reserved.