Various European Directives have been issued concerning the energy efficiency of the buildings. The target is the achievement of a near optimum energy efficient environment while at the same time satisfying occupant needs throughout the year within an integrated “holistici or “whole buildingi framework. A variety of different antagonistic parameters should be balanced such as window size and glazing transmittance or daylighting and shading and in most cases this requires an examination of various scenarios. Thus the design of building envelopes should address a careful balance between internal requirements and loads, the materials and properties of the façade and the external environment. Nowadays, the available tools for façade design-in terms of buildingis energy efficiency- are inappropriate for interactive or creative use. In this paper we examine the development of a genetic algorithm which is capable to optimise the opening areas, glazing properties and shading configurations -on the basis of minimum energy consumption- and then to design automatically simplistic alternative scenarios of the building façade