Benefits of Ivy

Thermal blanketing and weather shielding

Masonry walls are exposed to a range of climatic and environmental conditions, such as fluctuating temperature and changes in moisture content. These cause deterioration and erosion. In our research project, we monitored test walls for several years. The results show that a covering of ivy can create a microclimate with a more stable environment at the wall face. The ivy acts as a thermal blanket, protecting the stones, bricks, mortar and plaster from frost damage. It also shields the wall from heavy wind-driven rains. The beneficial buffering effects increase with the thickness of the ivy covering.

Moisture and damp

The effect of ivy on the moisture content of walls is complicated. There is no simple answer as to whether it increases or decreases damp. Its relative importance varies between different construction materials and locations, and between wall heights and aspects. A thick covering of ivy may shield walls from rain, but it may also stop damp (caused by ground moisture or building defects) from evaporating effectively.

Our research looked at deep-seated damp in walls, but found no evidence that ivy exacerbates deterioration associated with damp. Further research by the Royal Horticultural Society (RHS) and the University of Reading confirms that green walls with climbing plants, such as ivy, do not increase relative humidity and damp issues within walls.

Pollution and biological soiling

Pollution particulates can both soil and chemically degrade stonework. A covering of ivy traps fine airborne particulates, from traffic pollution for example. It also reduces the amount of salt-contaminated rain or traffic spray reaching the wall surface. By preventing light from reaching the wall surface a covering of ivy limits the ability of algae, mosses, liverworts and lichen to grow.

Wildlife habitat

As an evergreen, common ivy provides year-round shelter for birds and animals, and a place for butterflies to hibernate over winter. For example, the RHS has investigated the beneficial habitat for invertebrates provided by ivy on walls. The late summer/autumn flowers are an important nectar source for insects, such as bees, hoverflies and common wasps, holly blue and red admiral butterflies, and many moth species. The berries, which appear in November, are a good food source for blackbirds, black caps, collared doves, thrushes and robins.

Dense ivy growth is often used by nesting birds during spring and summer. Bats may also use ivy in the summer, and may even overwinter deep within very dense stands.

Work to cut back or remove ivy should be timed to avoid disturbing wildlife, particularly nesting birds.

Green walls

Green walls of living plants can provide an extra layer of insulation for occupied buildings. They help keep buildings warm in winter and cool in summer, thus reducing carbon emissions. They can also slow the rate of water run-off in built-up areas.

Common ivy, as well as other climbers, can be planted and trained as a green wall, but it needs to be carefully managed on historic buildings. As ivy can root into walls it should only be grown against masonry in good repair, and growth should be checked regularly.

The RHS and University of Reading research shows that common ivy is the best plant for summer cooling, compared to Boston ivy (Parthenocissus tricuspidata) and climbing hydrangea (Pileostegia viburnoides). In these research trials, ivy reduced the internal and external wall temperatures of model 'mini buildings' by 7.2°C and 5.7°C, respectively, compared to bare structures with no plant cover.

Unlike some other climbers, ivy is self-climbing and does not require a trellis for support. If rooted in the ground the plants probably do not need irrigation. However, green walls need to be maintained and kept lush to realise the cooling benefits. Ivy should be cut back if it is at risk of growing into roof spaces or rainwater disposal systems.