Casa Mas has been designed with the aim of achieving an high energy class building. The basement of the building is in concrete; the ground floor and the first floor are all realized in X-LAM technology. The integrated design of the building skin and the heating - cooling facilities has allowed to obtain the energy class A. High efficiency, high reversibility of structural components, low environmental impact, 80% reduction of CO2 emissions: Casa Mas is a model of a sensible architecture. The external original shape and the interior spaces have been designed following the analysis results of solar diagrams.