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The Future of Vegetative Roofs

  • Writer: Sophia Yang
    Sophia Yang
  • Apr 8
  • 6 min read

Updated: Apr 10

Roofs covered in plants were a common sight in Europe due to their insulating properties at a low cost. Yet, as urbanization increased, buildings were constructed to meet the needs of industrialization, and, with no space for them, green roofs fell out of fashion (Berndtsson & Emilsson, et al., 2006). However, these green roofs are making a comeback, both for their environmental benefits and aesthetics. 



Green roofs utilize vegetation and the space on top of buildings to improve air quality, drainage, energy efficiency, and more (Green Roofs). There are many types of green roofs, some of which include solar garden roofs that utilize solar panels and blue roofs that specialize in stormwater retention. Vegetative roofs incorporate plants and greenery to reduce the impact of environmental issues while maintaining aesthetics. There are two main types of vegetative roofs according totheir size; extensive roofs are shallow and require less maintenance, while intensive roofs are deeper and often boast parks with trees, thus requiring more maintenance (US EPA, 2014). 


Vegetative roofs are more complex than rooftop gardens: they use a series of layers built on top of a conventional roof. While the type of vegetative roof—either intensive or extensive—determines which layers a green roof will have, common layers include, from bottom to top: structural support, vapor barrier for waterproofing, insulation, root barrier, drainage layer with filter fabric, growing medium, and vegetation (US EPA, 2014). These layers work together to ensure stability and water management while reducing the possibility of leaks. 


Advantages

There are numerous advantages to vegetative roofs: these roofs reduce the heat island effect, which is when urban areas experience hotter temperatures than rural areas with natural landscapes because infrastructure like buildings and roads absorb and re-emit energy from the sun as heat (US EPA, 2014). Because plants absorb solar radiation without converting it to heat, any park naturally helps to cool down an urban area, but green roofs especially assist in this endeavor by covering black rooftops, some of the hottest surfaces in cities (Green Roofs). However, the exact reduction in air temperature varies depending on the composition, moisture, and height of vegetation: taller vegetation creates a cooler airflow, and moisture retention plays a key role in preventing air from getting too dry (Barriuso & Urbano, 2021).


Vegetative roofs have also proven to improve air quality. Urban areas release a large quantity of carbon dioxide into the air, but plants absorb carbon dioxide and release oxygen, thus reducing the greenhouse effect. Additionally, plants and their substrates, or growing mediums, capture pollutants and filter harmful gasses out of the air (Barriuso & Urbano, 2021). 


Furthermore, these roofs have a useful ability to slow down and reduce runoff water in storms, which is extremely helpful for modern drainage issues in urban areas. However, how much runoff a roof can capture depends on the design of the roof, rainfall patterns, and how big of a storm it is (Berndtsson & Emilsson et al., 2006). Nevertheless, this delay in runoff can decrease the stress sewer systems experience during heavy storms (Green Roofs). 


Energy efficiency can additionally be improved by implementing a vegetative roof. Plants on these roofs cool surrounding air through their natural process of evapotranspiration, the process when water is released into the atmosphere, thus minimizing the transfer of heat through the building roof (US EPA, 2014). By acting as an insulator for the building, these plants allow buildings to save energy on air conditioning and potentially heating, saving money in the process. 


Moreover, vegetative roofs play a role in noise reduction. In bustling urban areas, noise pollution acts as a serious problem. Plants can be used to absorb and scatter sound waves to dampen noise in the surrounding area. A 3.0 dB decrease in noise is equivalent to a 50% reduction in the discomfort caused by traffic, and a study from the European Commission found that greenery on roofs can reduce noise up to 7.5 dB (Barriuso & Urbano, 2021). 


All in all, vegetative roofs have a variety of benefits: they last longer than conventional roofs with proper maintenance, they increase biodiversity by providing habitats for plants and animals, and they also have social benefits for communities (GSA, 2021). Green roofs, depending on the type, can contain community gardens and provide recreational spaces, and they are more aesthetic than conventional roofs, thus adding value to the building (GSA, 2021). The sight of and interaction with nature has physical and mental health benefits, and can even reduce blood pressure and hospital stays (US EPA, 2014). Additionally, the production of green roofs creates job opportunities in design, manufacturing, and maintenance (Green Roofs). 


Disadvantages

However, the drawbacks to vegetative roofs are what make them less common in many places. Unsurprisingly, the main disadvantage of green roofs is the initial cost of installing one, which can be up to twice the cost of a conventional roof, if not more (GSA, 2011). However, despite the hefty installation fees, the longevity of the roof and money saved through energy conservation and stormwater management savings may make up for some of the cost (GSA, 2011).


Unfortunately, the price of a vegetative roof doesn’t end at installation. Maintenance is essential for a green roof in order to minimize leaks and ensure proper stability. Many of the issues that deter companies and people from installing green roofs come from improper maintenance, but nowadays, sensing technology can make maintenance more cost effective (GSA, 2011).


Another inconvenience that must be accounted for before implementing a vegetative roof is the increase in weight load. Given green roofs are built on top of conventional roofs, the roof and the building itself must be strong enough to support layers of soil and plants (GSA, 2011). Intensive roofs, which are heavier and contain trees and dense plants, require a greater increase in weight load that extensive roofs may not necessarily need. When retrofitting a historical building with a green roof, weightload information cannot be ignored.


Lastly, with dry conditions and increasing wildfires, fire protection should be sought for in every building. Vegetation, if properly moisturized, does not increase potential fire risks; however, shrubs and dead plant material and high wind exposure greatly increase a fire’s ability to spread, especially in dry climates (Gerzhova & Dagenais et al., 2022). Luckily, by removing dead material, having effective irrigation, and providing shade, maintenance will reduce the fire risk a vegetative roof may have.


Present and Future Implementations

Today, many countries have implemented a great deal of green roof architecture. Europe is at the forefront of green roof research, led by countries like Germany and Switzerland. Basel, Switzerland has the world’s highest green roof area per capita, as the city passed Building and Construction Law mandating all new developments with flat roofs to implement a green roof (Climate Adapt, 2020). The United States, Canada, and Singapore also have large markets for green roof technology, and cities like Chicago and Toronto have implemented a great deal of vegetative roofs. However, developing countries are put at a disadvantage when it comes to making this new technology widespread. In this case, small government loans and tax rebates promote green roofs, and mandatory policies naturally have large success rates (Durdyev & Koc et al., 2022). In some Southeast Asian countries where development levels aren’t evenly distributed and hot and humid climates impact green roof technology, adapting technology to fit the needs of each area is necessary (Pratama, Sinsiri, Chapirom, 2023). Moving forward, it is probable that this technology will only increase in popularity - it likely will be here to stay.


 

Written by Monisha Sevak


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