Ivy growing over the boundary wall at Rhodes House along Parks Road in central Oxford

A 3-year 'Ivy on walls - biodeterioration or bioprotection?' research project undertaken by the Oxford Rock Breakdown Laboratory at the School of Geography and the Enviroment has investigated whether ivy (Hedera helix) covering historical walls and buildings was deteriorative or protective.

The study covered England, with 5 field sites located in the north (Yorkshire), southeast (Kent), southwest (near Bristol), and central England (Oxfordshire, Cambridgeshire). Field investigations included using dataloggers to assess and compare temperature and relative humidity above and below the ivy canopy, examining how ivy interacts with dust particulates and pollutants, the construction of a test wall, and 2D resistivity surveys that measured stone moisture content. Laboratory work consisted of surveys of the stone surface at the micro-scale through scanning electron microscopy (SEM) as well as experiments into the physical breakdown of stone surfaces by penetration of ivy growth.

Results showed the bioprotective role of ivy on historical walls as an agent of thermal and moisture regulation and that ivy shielded walls from the pollutants that led to stone decay. The project's findings contribute to the lengthy debate on the role of ivy on historic structures and should influence future practice, management, and policy of ivy on walls.

The project was funded by English Heritage.