Energy savings during construction phases and the lifespan of the building are both important measures to reduce climate change emissions. As well as preventive measures during construction, reductions in embedded CO2, building design must consider measures to reduce energy consumption during the normal operation of the building. Particularly in the Mediterranean area, given the high number of sunlight hours and the high solar radiation levels, a decisive factor to maximize energy savings is to introduce natural materials for building envelopes and design passive solutions to improve indoor thermal climate control. Two techniques are analysed in this work: the use of dry Posidonia fiber to isolate the roofs of a real prototype building and, the use of cross ventilation design with the help of an electronic meter to decide when should exterior air flow through dwellings. Both techniques present different advantages in terms of energy savings in the Mediterranean area, allowing to construct and operate buildings more efficiently.