Some variables that are related to building shape and which influence heating and cooling requirements are the following: compactness index, the height of walls, climate, and the characteristics of the building envelope. These characteristics are crucial variables that should be taken into account because they are relevant to the energy requirements for maintaining the building at a comfortable temperature. This paper introduces a new approach to the description and modelling of multizone buildings in Saharan climate. Therefore, thermal nodal method was used to apprehend thermal behaviour of air subjected to varied solicitations. The result proves that proper use of compactness index and building geometry parameters will noticeably minimize building energy and improve the internal temperature of the building. The compactness is better when the compactness index is lower. (C) 2013 Elsevier B.V. All rights reserved.