A simple compact single dwelling shape reduces heat loss and maximizes performance in terms of passive solar gain. It is
considered that a modular system for the building would be most suitable to obtain a flexible structure that may be adapted to many sizes.To that end, the structure could be made by steel (pillars and rafters) which have maximum flexibility for interior spaces. In fact, the modular system that characterises the dwelling allows the increase/decrease in the size of the structure while it maintains the same proportions between spaces. In addition, the structure is as prefabricated as possible in order to reduce construction costs.