Extension of a 1935 home in Valldoreix. With insulation reaching a U-value of 0.16 W/m²K (well below the 0.53 required by the CTE), a vapour barrier and a ventilated façade, we showed that retrofitting to Passivhaus criteria is perfectly viable in existing buildings. The prefabricated timber structure, from sustainable forests, allowed a fast and clean execution. The project took part in the Endesa Awards 2012 in the retrofit category.