The building model is the most important and most difficult part of the energy modeling. All of the geometry data of the project i.e the energy zones with their envelope constructions (floors, walls, roofs etc) are set in this section. ECO-engine uses a powerful 3D building drawing concept in order to produce all the necessary data. In the building model section the user draws building blocks and splits them into energy zones by drawing internal walls or virtual partitions. During the drawing process all the envelopes are created automatically and are alight according to the set north direction.