Wall-to-Wall Gardening

Green technology goes vertical

Photo by the HOK Building Group

The practice of planting ivy to climb up the walls of buildings has existed for centuries. Now, the trend towards sustainability and green building practices can lead to the development and use of living walls as a means of filtering and improving a building’s indoor air quality. Green walls are a living, breathing, regenerating type of cladding that can be as simple as a living art installation or as complex as a biological air filter.

The first category of living walls is simply a vertical garden with all the benefits customary to a garden. Green walls, both indoors and out, decrease local CO₂, increase local humidity, trap dust, reduce noise and create a habitat for urban wildlife. Interior green walls can boost morale and productivity. The fresher indoor atmosphere keeps building occupants more alert and a feeling of overall health. Exterior green wall installations reduce solar gain (the entrapment of heat by passive solar gain on the building surface) and, by extension, building energy costs; provide protection from the effects of UV radiation and acid rain; and help lessen the building’s contribution to the heat island effect (when forest is replaced with concrete and asphalt, causing urban centres to become warmer than nature areas).

The second major category of living wall goes beyond these basic benefits by employing microbes within the planting substrate as a bio-filtering mechanism that removes potentially harmful hydrocarbons from a building’s ambient air. The bio-filtration system is structurally similar to the first type but is a closed loop system, controlling the circulation of the indoor air through the building’s mechanical equipment. Airborne, potentially harmful volatile organic compounds (VOCs) are drawn through the vegetative wall and then metabolized by microbes that naturally exist within the plant roots and planting medium before being re-circulated throughout the building. Plant species are specifically chosen for their VOC metabolic prowess and CO₂ and water are the by-products of the decomposition process.

Although the technology of biofiltration has been around for at least three decades, the practical application of green walls is a relatively new technology, so it’s not entirely trusted or proven. Alan Darlington and Michael Dixon, founders of Air Quality Solutions, have worked at correcting the historic problems of invading mosses and the clogging of porous lava rock by eliminating the use of moss and changing the base wall material. They’ve also decreased problems associated with high local humidity by changing from a misting to a drip water distribution system. They’ve been able to prove that continuous operation of a green wall doesn’t increase the amount of spores and allergens in the air, an issue that was a major roadblock to commercial success.

Despite the technical advances and positive findings of Darlington and Dixon it does not appear that there has been a dramatic increase in green wall installation over the past decade. Given the vitality of the environmental movement and the public acknowledgment that traditional HVAC filtering systems do not do much to alleviate sick building syndrome, it’s surprising that living walls have made little headway. It’s also surprising that outdoor green walls are not more prevalent given that it’s common knowledge they increase insulation and reduce building energy costs while providing an urban habitat and an aesthetically pleasing cladding system.

Arguably it’s the building designers’ responsibility to educate themselves and the client about the green wall systems and move passed this apparent hesitance to work with this technology.

Eddie Wu is a senior landscape architect and an industry-leading advocate of sustainable design solutions at The Group in Toronto.

Ashley Smith is a landscape architect focused on environmentally sustainable projects at The HOK Planning Group in Toronto.

This article appears in our January – February 2008 Issue