Unlike tall timber, green or living wall technology has yet to register as anything significant with the International Code Council (ICC). There is no task force seeking to conduct tests and present research, no committee to make recommendations to the voting membership. Green walls are not structural, so there is less of a critical need to reign them in with a governing code. But this doesn’t mean that setting clear standards for the burgeoning industry is necessarily undesirable.

“It is incumbent on people interested in [green wall systems] to come forward and provide ways for which the code can address it, and still be within the safety provisions that we have,” says Dave Bowman, manager of codes at the ICC. “I don’t think our regulations are a barrier for this technology.”

Codes that set a safe fire standard for green roof design may be applicable to vertical plantings in some cases, especially since walls using a foam-based or felt-based pocket system can be avenues for fire when not properly irrigated. Fire retardants can help with these systems, and steel or aluminum panels and cage structures (for vines) are quite safe, as are hydroponic systems without planting substrate.

A Localized Industry
Despite their relative safety and lack of regulatory obstruction, many parts of the country have yet to experience living walls. Even on the coasts, demonstration projects can still make an impact, such as the recent transformation of the Edith Green-Wendell Wyatt Federal Building in Portland, Ore.

Over a four-year stretch, from 2009 to 2013, the 18-story Edith Green-Wendell Wyatt Federal Building underwent a $139 million green makeover. The new structure is almost unrecognizable—gone is the generic International Style concrete and tinted-glass façade; in its place, a dynamic all-glass façade with protruding canopies clad in solar panels and reed-like steel shading appendages designed to encourage a tapestry of vines and a vertical habitat. The redevelopment achieved a LEED Platinum rating and a 50 percent reduction in energy use over the old building.

This type of suspended green wall system, an arm’s length from the building itself, opens the door to a more versatile and cost-effective vertical greening, especially involving retrofits. But any building protrusion also has its challenges. (ADA compliance for protruding objects states that “objects projecting from walls with their leading edges between 27 inches and 80 inches above the finished floor shall protrude no more than 4 inches into walks, halls, corridors, passageways, or aisles. Objects mounted with their leading edges at or below 27 inches above the finished floor may protrude any amount.”)

A little more than 600 miles south of the Edith Green building, in the Bay Area, founder and lead designer at Habitat Horticulture in San Francisco, David Brenner, has done many projects for private homes and Fortune 500 companies. The firm recently completed the largest vertical garden in the country: a composition of native redwood forest underbrush species rising several stories from a terrace at the San Francisco Museum of Modern Art.

According to Mike McCullough, business developer and biophilic design consultant with St. Paul, Minn.–based McCaren Designs, the Midwest is also showing signs of life. “We’ve been designing green walls since 1992, but just had our first Minnesota project in 2012 at the Ford Center.” One of McCaren’s projects from back in 1992 still draws attention today: a 3,500-square-foot green wall Rainforest exhibit at the Cleveland Zoo.

“Green walls are really building interest as a strategy to connect people to the natural environment to reduce the overall disconnect with nature,” McCullough says. “[Green wall systems] are becoming more interesting with public education around what they offer and what can be improved.” Although he concedes that after 25-plus years, the U.S. is still in the early adopter phase.

The International Example
Climate, cost, and performance will always be key variables in how fervently builders and policy makers move to adopt living walls. Subtropical regions are naturally suited to year-round exterior plantings and greater biodiversity, but the type of system can have major public health implications. Outbreaks of Dengue Fever in Malaysia, for instance, led to fines and restrictions on irrigation systems with standing water. The tray system, popular in the U.S., is nonstarter there.

Despite such limiting factors, there are often examples of progress and innovation specific to certain regions. In more northerly climes, moss is a plant of choice for efficiently cleaning city air and reducing the urban heat island. Berlin-based Green City Solutions pioneered CityTree a decade ago. This vertical moss plantation behaves as a fabric attached to buildings or moved about cities as a portable framed green wall. CityTree’s moss culture has far greater leaf surface area than any other plant, and can withstand temperature extremes. Its filtration potential is enormous; the company claims its 13-foot-tall, 10-foot-wide invention has an environmental benefit of up to 275 urban trees. At least 20 CityTrees have been installed in Europe and Hong Kong, with plans to donate some to India and other emerging nations with rapid, unchecked urbanization. Despite being cheaper with lower upkeep and water usage than competing green wall systems, moss has yet to make its mark in the U.S.

Moving the needle toward excess, architect Stefano Boeri interprets living walls as external vertical forests, building microclimates and enhancing air quality and livability on the scale of the neighborhood and city. Boeri hit his stride with Milan’s Bosco Veticale, a two-tower residential project for urban reforestation boasting some 900 trees and 20,000 shrubs and flowers on an intricate system of irrigated terraces. Boeri has since referenced this forested tower template for numerous concept designs and projects under development in the Netherlands, Switzerland, and elsewhere. He even has the world’s first master-planned green city under construction in southern China. Liuzhou Forest City will be home to 30,000 people with all its structures—homes, offices, hotels, hospitals, and schools—covered in plants.

Seductive as this work may be, these projects and full-scale green walls are expensive to build and maintain, and should be approached with a measure of restraint. And, short of holistic citywide greening, a building’s on-site greening and oxygen-producing benefits—with claims of complete purification being disproven, though air-quality improvements do exist—may be offset by walls that are over-irrigated and over-fertilized. “The industry has an incredible opportunity to improve the systems and address these negative externalities,” McCullough says. Connecting people to nature is great, but the design community has an opportunity to come together to establish best practices and push for enforceable environmental standards. “This is where more regulation would be a positive for the industry,” he says. It comes as no surprise then that green wall projects are often of a modest scale, located inside buildings, and more inclined toward beautification—it’s something a corporation or residential developer can add at limited cost to market their properties as healthy, enlightened spaces.

The vertical garden projects of Spanish company Paisajismo Urbano include such modest interior treatment, but also one of the world’s largest green walls in Bogotá, Colombia. Completed in early 2016, a patented system of vertical columns of bio-diverse plants was affixed to the exterior of the Santalaia building, climbing several stories and totaling over 33,000 square feet of coverage. Colombia, an emerging nation, boasts a handful of the world’s most impressive green walls.

Future Applications
McCullough notes a few prerequisites to the proliferation of living wall systems in the U.S. First, costs must be brought down. Offshore fabrication is already happening, and costs are still prohibitive for many. “Future savings will have to come through innovation in plant selection and irrigation,” he says. Second, plantings should become more resilient through the use of integrated hydroponic wall systems that impose no real restrictions on root systems. And finally, codes should be established to reign in environmental wastefulness and greenwashing.

In the wake of London’s Grenfell Tower disaster, questions are inevitable as to the fire safety of all types of external building cladding, living or not. London-based landscape architect and living wall specialist Shelley Mosco believes research is needed comparing the safety of different green cladding systems. Her Green Roofs and Living Walls Centre at the University of Greenwich—where she serves as a research assistant and senior lecturer—will look to run a trial to this effect. In her academic role, Mosco “advises living wall companies on latest research being undertaken by ourselves or our colleagues around the globe, to influence innovation.” As she told Horticulture Week in June, the center is researching living wall systems as primary cladding rather than secondary, potentially illuminating a host of new strategies for safety and durability.

As demand for living walls surges globally, for long-term viability, the industry must ally and press for standards that address the dual concerns of safety and environmental impact.