This has been a subject of debate for many years and has particularly exercised the minds of those involved in the heritage industry who protect, conserve and restore our architectural heritage.
Ivy may add character to walls, but it is commonly thought that it will damage walls where the existing mortar is already weakened or loose. It is reported that this will either allow water to seep in-between the joints, or stop moisture, making the wall dry and crumbly. Removal of the ivy will additionally cause further damage.
In an attempt to establish the true position, English Heritage commissioned research by a team from Oxford University’s Rock Breakdown Laboratory. This laboratory researches weathering and rock breakdown in natural environments. The project lasted three years. The team examined common ivy growing on walls in five different locations in England, each providing a different climate and situation.
The result of the research has just been announced. Their conclusion was that there was some evidence that ivy played a protective role shielding the wall from extremes of temperature and moisture which can cause cracks in the stone and damage to the mortar. The ivy was found to act as a ‘thermal barrier’. They also discovered less pollution and salts where the wall was covered by ivy. These pollutants and salts can lead to stone decay.
They did, however, confirm that where walls are already damaged, ivy would find its way into the cracks and holes and damage the structure further.
So it seems that providing the mortar and stone work is in good condition, the ivy can remain. Do note however, that this research was on perimeter walls, not house walls.
The research will allow English Heritage, and even the ordinary householder, to reconsider whether the ivy on their walls should be removed or left in place.
Oxford University School of Geography and the Environment: Ivy on walls – biodeterioration or bioprotection?
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