Green façades are effective passive systems for buildings, but the research about their winter effects is still few. This study investigated the influence of a green façade during winter nights in a Mediterranean area. The effects on microclimate and heat transfer were evaluated based on experimental data. These data were used to calculate radiative and convective heat transfer by formulae available in literature. The behaviours of the covered wall and a bare wall were compared. Vegetation allowed to keep the air velocity near the wall below 0.9 m s−1. The covered wall external surface and the nearby air recorded a warming of up to 3.4°C and 3.3°C, respectively. The walls lost radiative and convective energy, but for the covered wall these losses were 60% and 38% lower, respectively. Acting as a thermal and wind barrier, the green façade reduced overall heat losses by 57% improving building envelope performance.