Green Walls To Tackle Climate Change?

“To plant a garden is to believe in tomorrow”

—Audrey Hepburn

Carbon emissions generated through cities consume as much as 80 percent of energy production and account for a similar share of global greenhouse gas emissions. Mitigating increased temperatures in urban climates will increasingly become a priority as climate change progresses. The negative warming effects in cities should be a priority for governments, designers and planners around the world. Green walls can act as a passive system reducing energy demand and greenhouse gas emissions. However it’s important to take into consideration the type of system, the depth of the greenery, the design and the plants to be selected given that vegetation has a direct effect on thermal performance and its thermal conductivity and will vary according to these variables, among others.

green wall
Credit: Paul Hanaoka, Unsplash

Green walls have numerous positive environmental benefits that can be perceived by the users, being healthy clean air the primary according to a survey carried out in 2016. However, most of the respondents felt that vertical greenery enhances aesthetics in the city, and contribute to biodiversity and thermal comfort. The experimental monitoring showed how green walls can provide a cooler ambient temperature and reduce wind velocity creating an external microclimate during summer.

Surface temperatures differences have been recorded to reach up to 12°C lower in summer in Living wall systems. Ambient air can reach a temperature of 4.1°C lower creating a cooler exterior microclimate. Furthermore, wind speed can be decreased up to 0.7 m s-1 in front of a green façade and be reduced to nearly zero into the leaves foliage. This creates a layer of still air in between the foliage that performs as insulation with less temperature fluctuation.

Radiation can be blocked through the greenery through shading encouraging lower solar heat gain on the building envelope, hence lowering the surface temperature. Ambient temperature is decreased due to additional moisture in the air through evapotranspiration. The combination of these factors reduces the cooling load of the building, mitigates urban heat stress and climate change. However, there are some considerations to take into account like costs and maintenance of LWS (living wall systems). Due to the excessive costs of some LWS indirect facades can be a more accessible solution at present. However, for excessive temperatures, LWS can become a more sustainable economic option for future and extreme climates because of its improved thermal resistance (R).

Healthy sustainable cities should take into account future climates as a key factor to design spaces that provide comfort and a better quality of lives. The integration of green walls in buildings doesn’t necessarily need a large area of space in order to create cooling effects and provide numerous environmental and social benefits. Other cities around the world like Seattle have effective programs and policies encouraging new developments to have 30% percent of vegetation coverage. Singapore utilizes financial schemes to fund 50% of the costs of a green wall. London can benefit from similar policies to support the transition into a sustainable climate-resilient city. Green walls can be used as a strategy to improve the building energy performance in a temperate climate and reduce CO2 emission if used on a larger scale. More importantly, for most of us that don’t possess a garden, we can still create a natural zone that helps build a better tomorrow.