Boosting Energy Efficiency with Facade and Roof Greening

In times of climate change and increasing energy demand, energy efficiency is becoming increasingly important. Using energy efficiently can reduce greenhouse gas emissions and water use, among other environmental benefits. In addition, it can maintain stable electricity prices and reduce overall electricity demand. ¹ The energy sector offers numerous technologies and methods to enhance efficiency. Moreover, we can design our buildings to be energy efficient or use greenery to provide additional cooling. This blog post will explore how energy efficiency can be increased with facade and roof greening.

Advantages of Facade Greening for Energy Efficiency

Façade greening can decrease the amount of energy needed for cooling and, as a result, improve energy efficiency due to two phenomena: evaporation and the relatively high albedo of plants. Both contribute to how façade greening can lessen the impact of the urban heat island. Heat islands are urban areas which have a higher temperature than the surrounding area due to structures like buildings and roads which absorb and re-emit the sun’s heat. This creates a concentration of heat, relative to surrounding areas with more natural landscapes. ² But how exactly can façade greening reduce this urban heat island effect?

Firstly, façade Greening can reduce ambient temperature through evaporation because energy is required to evaporate water. ³ Plants use this evaporation process to uptake nutrients and regulate their metabolism. Consequently, the plant takes the energy needed for evaporation from the surrounding air in the form of heat, which causes the ambient air temperature to drop.

Secondly, facade greening cools a building, by shading it from direct sunlight. Furthermore, green facades have a higher albedo than normal ones. This means, that they can scatter more sunlight and lower the temperature in the microclimate. ⁴ How much energy do we save through these two cooling processes of façade greening? What do numbers say?

Saving energy with façade greening

Researchers at the University of Genoa examined the energy savings for heating and cooling in a virtual building with one south-facing greened façade . Due to the greening of the facade, they anticipate a 10–20% energy savings for air conditioning at the potential location. However, this economic benefit varies with the type of external wall.

Furthermore, façade Greening can also lead to additional thermal resistance by creating “a stagnant air layer in and behind the foliage” (Perini and Rosasco, 2013). As a result, façade greening can lower heating costs, though these savings are much smaller than those from cooling. In a building with a direct green façade, façade greening can decrease air conditioning costs by up to 1130 euros annually, while heating costs are saved by 7,41euros annually in the best-case scenario. However, Perini and Rosaco note in their paper that due to the high initial, maintenance, and disposal costs, the advantages of façade greening do not always outweigh the costs. Thus, to make façade greening economically sustainable, the government must offer incentives and tax deductions. ⁵

Green roofs for energy savings

Green roofs contribute in a similar way to energy saving as façade greening does. When compared to flat roofs, all types of green roofs offer energy savings throughout the entire energy life cycle. The amount of these savings depends on the type of roof greening and the climate zone and can vary from 8-31%. Extensive green roofs offer the highest life cycle energy savings with 15% – 31% dependent on the climate zone. ⁶

In addition, green roofs increase the durability of the underlying roofing materials through their protective effect. However, it must also be mentioned at this point that roof foundations can greatly increase the total water consumption of a house. This can be problematic, especially in regions with water scarcity. But also in this case, extensive green roofs perform relatively well compared to other green roofs. In a nutshell: Extensive green roofs may be sustainable solutions if high water requirements and installation costs are addressed through innovative technology and financial support. ⁶

Note: Assuming high maintenance costs for green roofs, they are a poor economic choice compared to flat roofs, if government subsidies are not considered. Subsidies of this kind can be part of an urban sustainability strategy and thus promote local action against climate change. ⁶

Conclusion

We learned in this blog post how we increase energy efficiency with facade and roof greening. To sum it up, green roofs and facades offer sustainable solutions for improving energy efficiency in buildings. Both can reduce the energy needed for cooling through plant evaporation and albedo. Research suggests that façade greening can lead to 10-20% energy savings for air conditioning and green roofs can save between 8-31% of energy, depending on the type and climate zone. While initial, maintenance, and disposal costs can be high, governments can support energy efficiency with facade and roof greening with incentives and tax deductions to make them economically sustainable.

Learn more about the subject of energy efficiency in my blog post about Technical Solutions for Intermittency in Renewable Energy.

References:

1. US EPA, O., 2017. Local Energy Efficiency Benefits and Opportunities. URL https://www.epa.gov/statelocalenergy/local-energy-efficiency-benefits-and-opportunities (accessed 5.2.23).
2. US EPA, O., 2014. Heat Island Effect. URL https://www.epa.gov/heatislands (accessed 5.3.23).
3. Facade Greening: A Way to Attain Sustainable Built Environment, 2016. International Journal of Environmental Monitoring and Analysis 4, 12. https://doi.org/10.11648/j.ijema.20160401.13
4. Mohammed, A.B., 2022. Employing systems of green walls to improve performance and rationalize energy in buildings. Journal of Engineering and Applied Science 69, 99. https://doi.org/10.1186/s44147-022-00154-9
5. Perini, K., Rosasco, P., 2013. Cost–benefit analysis for green façades and living wall systems. Building and Environment 70, 110–121. https://doi.org/10.1016/j.buildenv.2013.08.012
6. Koroxenidis, E., Theodosiou, T., 2021. Comparative environmental and economic evaluation of green roofs under Mediterranean climate conditions – Extensive green roofs a potentially preferable solution. Journal of cleaner production 311, 127563-. https://doi.org/10.1016/j.jclepro.2021.127563