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Green walls in Harvard University

Green walls in Harvard University (Daderot, Wikimedia Commons)

STEM in Context

Green Walls

Yevin Christine Cha

Summary

Green walls use plant processes to improve air quality in buildings.

Imagine walking through a field of green. You’re breathing in fresh air from all the plants around you. But you’re not outside in nature. You’re in a shopping mall! 

By 2050, 66% of the world’s population could be living in cities. As urbanization increases, the amount of green space in cities decreases. Urban designers and architects are finding ways of making buildings “greener” to help people in cities experience nature. One way of making a building greener is to give it a green façade or green wall.

What Are Green Façades?

On some buildings, climbing plants stretch over an entire wall. The plants are rooted at the base of the wall to create what is called a green façade. Today, you’ll find green façades on all sorts of buildings in a city, from houses to high-rise office buildings.

Did you know?

Ancient civilizations also used plants in urban areas. One example is the Hanging Gardens of Babylon (circa 600 BCE). Not everyone agrees that these gardens existed, but they are considered one of the seven wonders of the ancient world.

Green facade on an apartment building
Green facade on an apartment building (baona via iStockphoto).

What Are Green Walls?

Green walls, which are also called vertical gardens or living walls, are a newer type of plant wall. The plants growing on green façades are rooted at the base of the wall. But on green walls, the plants are planted directly into the wall. 

Did you know?

A person who specializes in taking care of plants and gardens is called a horticulturalist.

There are three main types of green walls:

  • Panel systems
  • Felt systems
  • Trellis systems 

Panel systems use wall panels with pre-planted plants. The panels are installed directly onto the wall of a building using a support structure.

 

 

Modular panel green wall system (Iran Green Agent
Modular panel green wall system (Iran Green Agent [CC BY-SA 4.0] via Wikimedia Commons).

Felt systems use a growing medium with felt pockets where you put the plants. Plastic pipes run through the wall,keeping the felt moist so the plants can grow.

 

Misting plants in a felt pocket system
Misting plants in a felt pocket system (tomazl via iStockphoto).

In a trellis system, plants grown in containers are trained (directed) to grow up a wall trellis. A trellis is a structure of wood or metal bars designed to support climbing plants. This system is similar to a green façade, except the plants are rooted in pots and not in the ground.

Climbing plants on an indoor trellis next to a window
Climbing plants on an indoor trellis next to a window (Foto_by_M via iStockphoto).

What Are Some Benefits of Green Walls?

Green walls have many benefits. First of all, they help clean the air that we breathe. Like all plants, the plants in green walls photosynthesize. That means they use sunlight, water and carbon dioxide to produce oxygen and sugars for energy. This process removes harmful carbon dioxide from the air and releases oxygen that we need to breathe.

Plants also have a natural ability to clean the air by absorbing pollutants and toxic chemicals. They do this through the microscopic holes in their leaves called stomata. Microorganisms (very small living creatures) living on and inside of plants can also help clean the air. They do this by breaking down toxic chemicals and releasing them back into the atmosphere in a form that’s less harmful. 

Green wall construction (2018) by Craighton Ellingsworth, President of GreenWall (1:24 min).

Did you know?

Scientists have genetically modified a common house plant to help clean the air. The plant breaks down 10 times as many pollutants as a regular variety. It’s called “golden pothos” or “Devil’s ivy.”

Green walls can also provide psychological benefits. According to the American Psychological Association, studies show that people who regularly see nature or have a view of trees from their school or office window feel happier. People tend to prefer the look of buildings that include natural elements, instead of just bare brick or concrete.

Green walls can also save money. For example, a building’s air-conditioning costs will be lower if it has a green wall. Air-conditioning requires a lot of energy. So a green wall means lower utility bills! 

What Is the Urban Heat Island Effect?          

As cities become denser, they also grow hotter. That’s because of a process called the urban heat island effect. New buildings end up crowded in a small area. The concrete in these buildings can store a large amount of heat. This heat gets released into the air over time. 

Scientists predict that between 2051 and 2080, many Canadian cities will see a yearly average of at least four times as many days over 30 degree Celsius. This is because of global warming and the urban heat island effect. Green walls can help tackle this issue. They provide shade from the sun and cool surrounding areas by preventing the concrete from overheating. 

Green walls can also help lower the surrounding air temperature through evapotranspiration. Evapotranspiration is the combination of two different processes: evaporation and transpiration. 

Evaporation is the conversion of liquid water to water vapour. The evaporation of water from the surface of plants’ leaves takes energy from the surrounding environment. Since heat is a form of energy, heat energy will decrease around the green wall. As a result, the temperature goes down. 

Transpiration is essentially how plants breathe. Liquid water travels through the plant. It is converted to water vapour as it exits through the stomata in plants’ leaves. Transpiration uses the same principles as evaporation. Converting liquid water to water vapour removes heat from the surroundings. This lowers the overall temperature. 

Maintenance being done on a green wall in Spain
Maintenance being done on a green wall in Spain (AlejandroOrmad [CC BY-SA 3.0] via Wikimedia Commons).

Are There Any Downsides to Green Walls?

Green walls require regular upkeep. On average, they have 50 plants per square metre. That’s a lot of gardening! Maintaining green walls that contain soil comes with other challenges. The biggest challenge is keeping the soil in the wall. As the plants grow, soil gets knocked out. Plants also need to be replaced as they get larger and no longer fit on the wall.

With indoor green walls, drainage can also be an issue. If the proper systems aren’t put into place, then the plants may receive too much water. Overwatering can lead to mould or cause the plants’ roots to rot. Rotten roots can kill a plant.If the irrigation (watering) system isn’t correctly installed, it can also cause water damage to the wall itself. 

Did you know?

Green walls help purify the air, filtering various allergens from furniture and indoor machines. This can help with allergies!

Green walls are also expensive to install. The average cost is between $900 and $1 500 per square metre. This makes them a luxury item. However, many experts believe that their overall benefits outweigh the initial cost of installation.

Summing up...

As the world urbanizes, we need to find new ways of bringing the benefits of nature into cities. One way of doing this is by growing more green walls. They will help people in cities reconnect with nature and find comfort in the shade.

Starting Points

Connecting and Relating
  • Have you ever seen a green wall in person? Where was it? What did you think of it? 
  • Do you like to have plants in your home or in the indoor environments you visit regularly? Why or why not?
  • Where would you consider building a green wall to enhance an indoor space? Explain.
  •  
Connecting and Relating
  • Have you ever seen a green wall in person? Where was it? What did you think of it? 
  • Do you like to have plants in your home or in the indoor environments you visit regularly? Why or why not?
  • Where would you consider building a green wall to enhance an indoor space? Explain.
  •  
Relating Science and Technology to Society and the Environment
  • Looking ahead, should it become mandatory for all new public buildings to have green walls? Why or why not? 
  • Would it be better for all levels of government to support building and maintaining outdoor urban green spaces or to encourage creating indoor spaces with green walls? Explain.
  •  
Relating Science and Technology to Society and the Environment
  • Looking ahead, should it become mandatory for all new public buildings to have green walls? Why or why not? 
  • Would it be better for all levels of government to support building and maintaining outdoor urban green spaces or to encourage creating indoor spaces with green walls? Explain.
  •  
Exploring Concepts
  • How do green walls affect air quality? Explain.
  • How is a green façade different from a green wall? 
  • What are the three basic types of green wall systems? How do they differ?
  • What is an urban heat island? How do green walls help reduce heat?
  •  
Exploring Concepts
  • How do green walls affect air quality? Explain.
  • How is a green façade different from a green wall? 
  • What are the three basic types of green wall systems? How do they differ?
  • What is an urban heat island? How do green walls help reduce heat?
  •  
Nature of Science/Nature of Technology

  • How is the science of psychology informing the design of indoor spaces? 

Nature of Science/Nature of Technology

  • How is the science of psychology informing the design of indoor spaces? 

Media Literacy
  • Where have you noticed green walls featured in popular media (e.g. TV programs, magazines, online blogs or articles, advertisements)?
Media Literacy
  • Where have you noticed green walls featured in popular media (e.g. TV programs, magazines, online blogs or articles, advertisements)?
Teaching Suggestions
  • This article can be used to support teaching and learning in Environmental Science and Biology related to horticulture, photosynthesis, plant processes and air quality. Concepts introduced include urbanization, green façade, green walls, vertical gardens, panel systems, felt systems, trellis systems, trained (plants), photosynthesize, pollutants, stomata, microorganisms, urban heat island, evapotranspiration, evaporation and transpiration. 
  • After reading this article, teachers could have students conduct a Concept Definition Web learning strategy to consolidation their understanding of the concept of green walls. Ready-to-use Concept Definition reproducibles are available in [Google doc] and [PDF] formats.
  • Teachers could also have students consolidate the information presented in the article by creating a graphic organizer or infographic that compares the different types of green wall systems. See the Infographic Creator learning strategy. 
  • To go further, teachers could use the Issues & Stakeholders learning strategy to have students consider the installation of a green wall system from the perspective of different stakeholders (e.g. architects, staff working in the building, members of the public, clients, maintenance staff, building owner, etc.). Ready-to-use Issues & Stakeholders reproducibles are available in [Google doc] and [PDF] formats. 
  •  
Teaching Suggestions
  • This article can be used to support teaching and learning in Environmental Science and Biology related to horticulture, photosynthesis, plant processes and air quality. Concepts introduced include urbanization, green façade, green walls, vertical gardens, panel systems, felt systems, trellis systems, trained (plants), photosynthesize, pollutants, stomata, microorganisms, urban heat island, evapotranspiration, evaporation and transpiration. 
  • After reading this article, teachers could have students conduct a Concept Definition Web learning strategy to consolidation their understanding of the concept of green walls. Ready-to-use Concept Definition reproducibles are available in [Google doc] and [PDF] formats.
  • Teachers could also have students consolidate the information presented in the article by creating a graphic organizer or infographic that compares the different types of green wall systems. See the Infographic Creator learning strategy. 
  • To go further, teachers could use the Issues & Stakeholders learning strategy to have students consider the installation of a green wall system from the perspective of different stakeholders (e.g. architects, staff working in the building, members of the public, clients, maintenance staff, building owner, etc.). Ready-to-use Issues & Stakeholders reproducibles are available in [Google doc] and [PDF] formats. 
  •  

Learn more

Our World in Data: Urbanization (2018)

Article by Hannah Ritchie & Max Roser which discusses global urbanization, with data and interactive graphics.

DIY Sub-irrigated Green Wall (2017)

Short documentary video (5:35 min.) by Plant One On Me about a young woman in New York who has hundreds of plants in her apartment. Includes information about how she takes care of the plants and about the systems she’s put in place to help them grow.

Living Off the Wall… Literally (2013)

Article by Jean-Marc Dufrense, University of Ottawa which discusses living walls, including information about a very tall living wall at the University of Ottawa.

References

BBC. (n.d.). What is photosynthesis?

Climate Atlas of Canada. (n.d.). Urban heat island effect.

Loh, S. (2008). Living walls - a way to green the built environment. BEDP Environ Des Guide, 1.

Prendergast, D. (2015, December 1). The pros and cons of a living wall from the garden gnome. Spirit News.

Ritchie, H., & Roser, M. (2018, September). Urbanization. Our World in Data.

Urban Green-Blue Grids. (n.d.). Green facades.