Ivy on Walls
Ivy (Hedera helix) is commonly found growing over walls. A covering of ivy may not necessarily be harmful as it can protect surfaces from weathering processes. However, ivy can sometimes root into a structure and this is likely to cause damage.
Historic England has researched the benefits and problems caused by ivy and this can be found in our Ivy on Walls research report.
Physical damage by ivy growth
The potential for ivy to cause damage to historic walls is primarily controlled by the condition and physical characteristics of the underlying structure.
Ivy cannot actively 'bore' its way into walls but it can cause serious problems where it grows into existing defects such as holes, cracks and crevices. Where defects do exist ivy stems can grow into them and may push stones apart or dislodge them.
The potential for damage can be minimised through appropriate management, including regular pruning to prevent growth onto roofs and over guttering, and removing excessive arboreal growth.
Rooting-in
The greatest damage often occurs when ivy 'roots-in' to walls. This is not common but can be stimulated when shoots come into contact with darkness, moisture and weathered material (protosoil) within already deteriorating walls.
The common practice of killing ivy by cutting it at its base can also stimulate rooting-in and this is no longer recommended.
Surface attachment: juvenile ivy stems attach and climb up walls via aerial rootlets. Attachment is remarkably strong but is entirely superficial – aerial rootlets do not penetrate into the materials they are attached to, and they do not extract moisture or nutrients (the same is true for ivy growing on tree trunks). Forceful removal of stems can cause physical damage to the substrate underneath, and it may leave marks that may be an aesthetic issue for some assets.
Microclimate buffering and weathering
Ivy is very effective at reducing extremes of temperature and relative humidity, and the frequency and range of variations that can otherwise contribute to deterioration over time. Ivy also reduces the frequency, severity and duration of frost events that cause damage to vulnerable masonry materials.
Surface soiling and pollution filtering
Ivy foliage is an effective trap of fine airborne particulates. It reduces the amount of pollution reaching the surface of walls that contributes to soiling and chemical degradation. Ivy cover can limit greening or blackening of stone (by algae growing within the stone matrix) through its shading effects.
Moisture
The influence of ivy on the moisture content of walls is complicated and 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 different wall heights and aspects.
A thick cover of ivy certainly shields walls from rain, but it may reduce evaporation of ground-level moisture where there is an existing damp problem.
Long-term monitoring of test walls shows that a covering of ivy typically stabilises surface humidity to levels well within the typical range of moisture variations found on exposed wall surfaces.
There is no evidence that ivy influences deeper-seated moisture in walls.
