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Will Ivy Covered Walls Come Tumbling Down?

Q. Mike: Does English Ivy damage structures? Web searches have turned up mixed answers. Some on campus want it off; others like the way it looks. The buildings in question are mostly wood, some masonry, approximately 100 to 150 years old. Our carpenter is concerned that the ivy is holding moisture and providing a highway for ants and other destructive insects to get to the wood, which never gets sun or a breeze, and is always damp. Thanks,

---Andy; Director of Facilities; Ursinus College; College ville, PA

A. With questions like this, I always reach out to the American Ivy Society ; and was delighted to find that Russ Windle—who helped us discuss the issue of ivy on trees many moons ago—was still their Director of Research. He sent me a number of studies to review but also warned that when people complain about "English ivy", the culprit is frequently a different vine—often the more aggressive "Irish Ivy", or something like Virginia Creeper. (As I drove through Center City Philly recently, I noticed that the majority of "ivy covered walls" were covered with plants that were not ivy.)

So that's job #1: Have your specific climbing plants professionally identified.

Now, the Society has produced an 'annotated reference list' that delivers Abstracts on 18 different articles on the topic. Most of these papers appeared in ivy journals—under titles like "dispelling the myths", "false accusations" and "in defense of ivy"—and make the case that true English ivy poses no danger to a solid wall with sound mortar, and may actually insulate walls against extreme changes in temperature. And, rather than keep them wet, it is suggested that true English ivy, with its waxy coating, may divert rain away from the wall and keep the surface drier. (This highlights the importance of knowing what you got, as other climbing vines may not have water-shedding leaves.)

An article from the Brick Institute of America that appears on the list pretty much sums up the issue with its opening line, "there is no single easy answer." They conclude that it is possible that ivy could dislodge "masonry units" of walls not properly constructed. (And that's a line you hear over and over—the better shape the wall was in before the ivy appeared, the less you need to worry). They also note that ivy growth might keep moisture trapped against the wall or might act to shed rainwater. Worried custodians are advised to remove a small area of ivy for inspection.

A recent lengthy report out of Oxford University (funded by English Heritage and the National Trust) examines the effects of ivy growing on truly old buildings in England. One interesting finding is the role of "ivy as concealer"; the researchers found that some of the buildings had important architectural features that were being hidden by the ivy—plaques, statues in alcoves, inscriptions and such, and that study of the building's historical features had become impossible without removal of the ivy.

But when the ivy WAS removed, most of the area it was covering was found to be "in astonishingly good condition". In addition, rigorous scientific studies concluded that ivy growing on walls provided excellent insulation—moderating daytime temperatures on the other side of the wall by 36% and nighttime by 15%. (Now we're approaching 'Green Building' usefulness!)

Dampness was harder to pin down, but in general, they found that areas under ivy were less humid than unprotected areas. Perhaps most striking was the protective effect against particulate air pollution in high-traffic areas. Ivy clearly kept these staining, discoloring pollutants off the walls—a huge benefit, as I've personally seen the damage air pollution has done to many of Philadelphia's great historic buildings. (When the tower of City Hall was cleaned a while back, it completely changed color.)

And what of the famed 'Ivy League'—the group of colleges named either for their ivy covered buildings, or, as some historians suggest, for the Roman Numeral IV as there were four of them in the original group? Turns out that many of them are covered in Boston 'ivy' (Parthenocissus tricuspidata)—an aggressive plant that is not an ivy of any kind. Ah but Founding Member Princeton University, whose buildings are adorned with true English Ivy, has made a clear pro-plant choice . When it came time for stone work on some of the buildings to be re-pointed, the ivy was carefully removed, attached to scaffolding and replaced when the work was done.

But these are all stone structures, and I could find no reference of any kind for ivy growing on wood, so my suggestion is to follow the advice of the Brick Institute and uncover and inspect a few areas visually. I would also begin measuring the relative humidity under the vines and against bare surfaces. If the area is being kept damp, the ivy should be removed. But if the buildings are sound, and the ivy is true, Ursinus might turn out to be unique—you'd be in an Ivy League of your own!

The American Ivy Society Presents:

Annotated Reference List
Compiled by Dr. Sabina Mueller Sulgrove, Director of Ivy Research
American Ivy Society, P.O. Box 2123, Naples, Florida 34103-2123 USA

The Ivy League:

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