Hedera helix is the most effective plant cover for cooling buildings during hot summer months. This has been found in research carried out by the Royal Horticultural Society and University of Reading.
The RHS and the university have investigated the impact of green walls on the temperature and relative humidity within buildings. The walls were covered with three plant species: Hedera helix (ivy), Parthenocissus tricuspidata (Virginia creeper) and Pileostegia viburnoides (evergreen climbing Hydrangea).
All species reduced the air temperature, both inside and outside the building by at least 1°C compared to bare buildings. Hedera helix proved to be the best cooling plant: the internal wall temperature dropped with 7.2°C and the external wall temperature with 5.7°C. Ivy showed also the best results during warm winter afternoons: the relative humidity was 5.7% lower inside the building, compared to buildings without ivy covered walls. This means that these walls would keep buildings less humid in winter months.
According to the RHS, green walls with climbing plants are ideal for confined spaces. There have been concers in the United Kingdom that such walls may increase the humidity inside buildings and may cause damp issues, but the research demonstrates the opposite.
Photo by RHS