The role of shrubs and climbers on improving thermal performance of brick walls during winter

Thermal regulation is increasingly cited as one of the ecosystem services provided by urban plants. In addition to summer cooling, plants can help insulate buildings against heat loss in winter. Research was conducted using replicated small-scale physical models to simulate buildings and cavity walls and to investigate the insulation properties of plants during cold weather. Covering heated cuboids with ivy (Hedera helix) reduced energy consumption by 20-30% compared to non-covered cuboids. Parallel work with wall shrubs monitored temperature profiles on the exterior and internal cavity of walls. The presence of shrubs enhanced temperatures significantly compared to bare walls. Temperature differences were affected by weather parameters, aspect, time of day and plant morphology. For example, Prunus laurocerasus with dense foliage of large evergreen leaves proved a better insulating species than Cotoneaster franchetii (with fewer, smaller, narrower leaves). Similarly, a double row of Prunus plants gave greater insulation than a single row. These empirical studies with replicated treatments augment previous research based on urban modelling and data from non-replicated individual buildings in situ. They also indicate that plant choice and planting design requires more attention to ensure the heat saving aspects associated with green walls and shelter belts are optimised. These aspects are discussed within context of wider urban ecosystem services provided by shrubs/wall climbers.