Design Goals and Green Wall Benefits

The benefits of green wall systems apply not only to the individual buildings that they are a part of, but also their surrounding community. Indeed, a concentration of buildings with green walls has the collective potential to make a dramatic impact on that community. This concept was developed and popularized in the Garden City Movement in England and in the US in the 1900’s and continues today. Further, the work of the US Green Building Council and the LEED® program has promulgated the building specific and community benefits of creating green buildings, some of which can be accomplished through green wall systems as discussed further below:

• Urban Heat Island (UHI) Reduction. The urban heat island (UHI) effect is the temperature increase in urban centers caused by the replacement of “natural vegetation with pavements, buildings, and other structures necessary to accommodate growing populations” (Wong 2005). These impermeable surfaces convert sunlight to heat, while the disappearance of vegetation and construction of tall buildings prohibit the occurrence of natural cooling processes such as evapotranspiration and wind. UHI has been shown to increase the incidence of smog days and summer time demand for cooling. It has been reported that as many as a thousand people in the US die each year due to extreme heat, a figure higher than all other weather events combined. The reintroduction of vegetation into urban environments promotes the occurrence of natural cooling processes through evapotranspiration since the sunlight absorbed by vegetation would otherwise be converted into heat energy.  These processes contribute significantly to the reduction of ambient temperature in densely packed urban environments.  Furthermore, with strategic placement of green walls, plants can create enough turbulence to provide wind breaks cooling air at the same time as it slows it down.

• Building Energy Efficiency. Greening a building’s envelope is one technique used to improve its thermal properties through external temperature regulation. Those structures located in more extreme climate zones are exposed to a higher degree of fluctuating conditions and require more energy to maintain constant interior conditions than those in milder climates. Green walls have been shown to reduce temperature fluctuations at the wall surface from 5 to 30 ºC (41 to 86 ºF). The natural processes that contribute to this improved energy condition include wind, shading, and evapotranspiration.  

• Improved Exterior Air Quality. Air quality is directly linked to the UHI effect.  A reduction in urban temperatures (e.g. through the reintroduction of greenery) would positively affect air quality through the reduction of smog days and the reduction of air born particulates. Beyond the temperature benefit, plants directly absorb carbon dioxide while giving off oxygen in their life-dependent process of photosynthesis. This natural air filtering and processing of one of the more significant greenhouse gases is a notable improvement to air quality. Further, plants can act as collection sites for dust and other air particles. Leaf surfaces collect dust particulates until they are washed to the ground during a rainstorm. The degree to which plants can fulfill this air quality improvement function depends upon the Leaf Area Index (the ratio of total upper leaf surface of vegetation divided by the surface area of the land on which the vegetation grows) meaning that, the greater the leaf surface, the more particulate matter a plant or green wall will retain.  Therefore, dust and particulate matter counts can be reduced by as much as 75 percent downwind of urban plantings. Similarly, fumes and bad odors can be intercepted by plants or even masked by the scent of some plants to further improve air quality.

• Improved Interior Air Quality. Living walls located inside of buildings can directly contribute to improved interior air quality. It is commonly acknowledged that most North Americans spend 80 to 90 percent of their time indoors and as a result are highly influenced by the effectiveness of interior air circulation systems. Poor indoor air quality can be caused by such things as inadequate ventilation and chemical contaminants from indoor or outdoor sources. Scientific testing has established a list of indoor plants that have the ability to filter at least three of these chemical contaminants: benzene, formaldehyde and trichloroethylene. Benzene is a solvent used in ink, oil, paint, plastic and rubber. Formaldehyde is present in virtually all indoor environments: urea formaldehyde resins are used in foam insulation, particleboard and pressed-wood products; it is also present in tobacco smoke, natural gas and kerosene. Trichloroethylene is used in metal degreasers, dry cleaning solvents, inks, paints, lacquers, varnishes and adhesives.  Green walls that use appropriate plants can act as natural “bio-filters” for these chemicals as well as others when implemented as part of an integrated building strategy.

• Urban Agriculture. There is an emerging trend to grow more local food, particularly in urban locations. Green wall systems are well suited for this possibility as long as several design factors are addressed that influence their ability to produce food. These include the level of desired maintenance (food growing and harvesting requires more maintenance than ornamental plants), the level of nutrients available, sun exposure, and the height of building.

Chef Mario Batali's Pizzeria Mozza restaurant in Los Angeles grows a variety of vegetables and herbs on this living wall on premises. Photos courtesy of Tournesol Siteworks LLC

• On-site Waste Water Treatment. Currently, cities occupy approximately 2 percent of the surface of the planet but house 50 percent of the inhabitants of earth. Every day 180,000 more people become city inhabitants. All of this population creates, among other things, a demand for waste water treatment. Innovative ways to naturally treat waste water on site are being seen in some of the most urban areas. For example, the proposed Editt Tower in Singapore is under construction and is an attempt to address this issue. According to Ken Yeang, Architect, it will house “a fascinating system of water collection… involving a sculptural rain scoop on the roof and a system of water collection that scallops down the façade combined with a proposal to recycle gray water through soil filter beds in the vertical landscaping.”

• Increased Biodiversity. Biodiversity is defined as the variation of life forms within a given ecosystem. Biodiversity boosts the overall ecosystem productivity where each species, no matter how small, all have an important role to play in that ecosystem. The benefits of biodiversity, even in urban environments include stabilization of local ecosystems overall and aesthetic and psychological benefits for inhabitants. However, despite the benefits of designing for biodiversity, not all building owners would like to attract wildlife and would rather repel insects, birds, and mammals. It is possible to discourage their presence through careful design of a green wall. One of the primary techniques used to repel wildlife is the selection of plants that do not fruit, go to seed or offer a food source. Similarly, climbers with small leaves and with a thinner profile cannot provide nesting sites for birds and small animals. Projects with thick layers of foliage can be pruned once a year and deadwood removed to limit this occurrence. 

• USGBC LEED® Credits. Currently not many green wall projects have been specifically LEED® certified, since they are not explicitly incorporated into the standard. Nonetheless, green walls can contribute to points in all of the categories of this voluntary rating system. Since LEED® has been adopted by many municipalities as a minimum construction standard the use of green walls can help achieve certification at any targeted level.

• Marketing and Green Branding. The trend of users and developers toward greener buildings continues to be an important marketing consideration. Part of this phenomenon is related to the commitment of so many people to green technologies including green procurement, green roofs, and green walls. According to facilities.net “In New York City, landlords with attractive green features are definitely able to charge a premium. Tenants interested in green features are either petitioning landlords to make green improvements to space they already lease or are doing their own green renovations.” This trend is fueled in part by employers that are finding easier employee recruiting and lower employee turnover in green buildings. Developers are also finding easier lease outs, lower turnover of tenants, and increased property value due to increased efficiency.

• Building Façade Protection. It is a common misconception that green walls will always damage the structure to which they are affixed.  If the building façade is in good repair then clinging vines or other plants will not threaten its integrity. However, when a façade is in poor shape or defective, plants should be grown on a separate structure (e.g., metal cables or trellises) that is kept away from the wall. If periodic maintenance of the building façade is required, then the green wall system should be able to be removed or hinged out of the way while keeping plants intact. Of course, damage to a building structure or façade can in fact be caused by other things such as UV radiation, rain, snow, wind, and thermal variation. A green wall, whether a green façade or living wall system, will shield the building from all of these things and can thus help to extend the useful life of the building façade.

• Aesthetic Improvement. Aesthetic improvements in clinical settings have been demonstrated to lead to psychological improvements (e.g. increased patient recovery times). But in the everyday built environment, (exterior and interior) things such as blank or stark concrete walls and fences along transportation corridors and buildings are hardly an appealing aesthetic and are described more as blight on the landscape. These areas are opportunities for improvement through greening.

• Noise Reduction. In some cases, green walls can be used to soften or deaden sound inside or outside of buildings. Factors that affect a green wall’s ability to reduce noise levels include depth and composition of the substrate or growing medium as well as the plants selected and their overall coverage.

• Local Job Creation. Green walls draw upon multiple disciplines for their design, installation and maintenance. As the demand for this technology increases, so will the demand for professionals who specialize in green wall installations.