The role of rooftops in healthy sustainable building designs
Why Green & Healthy building Rooftops?
Roofs can take up to 15-35% of the total land area of a city, making them a vital surface in urban settings (“Urban”). This often underutilized area of a building envelope can provide smart, healthy, and environmentally friendly design options that are increasingly being executed across cities.
The implementation of green roofs within a sustainable building strategy, for example, can provide benefits such as:
a reduction of Urban Heat Islands
increased energy efficiency
improved rainwater management
improved biodiversity
the provision of amenity spaces
Green roofs are the most holistic and multifaceted design strategy for these surfaces, but other considerations such as cool roofs, the incorporation of rooftop gyms or exercise areas, and solar panels are a few examples of smart rooftop design that contribute to a healthy building or sustainable building strategy.
Sustainable building rooftops Reduce Urban Heat Island Effect
One of the most important influences that rooftops can have is a reduction of Urban Heat Islands (UHI). This phenomenon describes the prevalence of higher temperatures that arise in dense, urban regions, due to the presence of man-made surfaces with higher heat retaining properties than those in natural environments.
Out of the entire building envelope, roofs are subject to the highest amount of solar irradiance, making their albedo properties the most important to curb the effects of UHI (Costanzo).
With the rise of temperatures across the globe comes the rise of heat related deaths. Increased respiratory disease, heat stress, reduced productivity, discomfort, and mental health challenges can all also occur due to increased warming (Swain).
With UHI compounded with the rising temperatures, the physical health and wellness of those residing in cities becomes more dire—making it an essential problem to address.
The most common strategies to reduce UHI on roofs is to implement cool or green roof strategies. Cool roofs use highly reflective coating such as white paint to reduce heat absorption, while green roofs implement plants and other vegetation, which acts as insulation and a cooling mechanism for the building and surrounding microclimate.
Increase Energy Efficiency via green rooftops
The implementation of smart roof design has the potential to greatly increase building energy efficiency. For one, green roofs can reduce building cooling loads and therefore increase HVAC efficiency. Also, Solar panels can be implemented on roofs to grow renewable energy use.
When used in tandem, green roofs and solar panels can be implemented on the same roof and provide dual benefits.
Generally, roofs are dark, heat absorbing surfaces that have the potential to raise building temperatures and increase cooling demands. Plants and greenery naturally reduce the temperature of roofs and add an insulation layer, diminishing the amount of hot and cold air affecting the building’s temperature, further regulating it.
In addition, the cooler microclimate created by rooftop greenery can increase the efficiency of rooftop HVAC systems (“Green Roof Benefits”).
In addition, solar panels can be placed on rooftops to act as a renewable energy source for a building. Although usually thought of separately, if a green roof and solar panels are used together, known as a biosolar roof, the benefits increase.
Like rooftop HVAC systems, solar panels work more efficiently in cooler climates, making the combination of vegetative cooling and solar panel energy creation a beneficial, symbiotic relationship (“Green Roofs-Solar”).
Improve Rainwater Management on green rooftops
Rainwater management and collection is a commonly mentioned concept in many building certification and rating systems, and can be improved through the implementation of green roofs. Impervious surfaces and hardscapes cause excess water runoff, which can disrupt natural hydrology and ecosystems, as well as contaminating water bodies with pollutants.
Pervious surfaces that allow for water absorption, capture, and reuse can be implemented through green roofs and through the incorporation of surfaces such as porous pavement or grid pavers.
Green roofs can capture the water as it falls, and filter out its pollutants naturally, reducing the burden on sewer systems and avoiding flooding, as well as preventing toxins from entering water bodies. It has been found that green roofs can hold 70-90% of the rain that falls on them in the summer, and 25-40% in the winter (“About”).
Once captured, this water can be redistributed throughout the building such as in irrigation, toilets, and other non-potable uses.
The use of green roofs and pervious landscaping can greatly impact rainwater management and reduce water demand within buildings.
One study done by researchers at Pennsylvania State University found that green roofs retain around 80% of fallen water, while traditional roofs captured closer to 24% of rainfall (“Green Roof Benefits”). However, when designing roofs for rainwater capture and reuse, it is essential that loads are calculated, and proper sealing of the building envelope is executed to avoid any leaks.
Improve Biodiversity with a green rooftop
Cities are barren compared to the natural world, and therefore provide fewer habitats for flora and fauna. Implementing green roofs within urban regions is a way to use often underutilized spaces to increase the presence and diversity of species within the built environment.
Increasing biodiversity in cities can not only improve the health of those ecosystems themselves, but also the systems that function around them--such as the hydrological or nutrient cycles. In addition, from a mental health standpoint, the visual presence and interaction with a diversity of species can be positive for human well-being (“About”).
Plants, especially native species promote the livelihood of birds, insects, and butterflies and restore the ecological cycles that are often disrupted in cities. In addition to providing an immediate habitat for animals, green pockets can provide places of respite for animals and provide more closely connected habitats for migrating birds and other species that would otherwise be fragmented by cities (“About”).
In addition to greenery, when solar panels are implemented as well on biosolar roofs, they can provide additional landscape diversity. The panels provide shade and protection, as well as a place for water runoff, creating a wetter side and a drier side. The implementation of PV can therefore cause a “habitat mosaic”, attracting a wider variety of flora and fauna and further increasing biodiversity (“Green Roofs-Solar”).
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Provide Amenity Spaces with a healthy building rooftop
In addition to the ecological benefits of green rooftops, they can also provide social and mental health benefits for building users. Strategies such as rooftop gyms and community gathering spaces can provide further benefits.
Outdoor exercise has been proven to have additional benefits when compared with traditional exercise, such as greater mood improvements, decreases in anxiety and increases in the desire to be active. Due to the mental and physical health benefits from both nature exposure and exercise, the combination of the two provides even greater gains (Loureiro).
Implementing exercise spaces and gyms on rooftops is an impactful way to improve the health and wellness of building users, while avoiding building footprint increases.
In addition, publicly accessible rooftops can provide places of respite and locations to gather as a community. Community gardens can be placed to encourage building users to spend time outside in nature, provide educational opportunities, improve nutrition and food awareness, and reduce the local community’s food footprint (“About”).
Finally, aesthetic roofs with various amenities can encourage occupants to utilize the space for events and social gatherings, further promoting community, connection to the outdoors, and overall wellness.
Sources
“About Green Roofs.” Green Roofs for Healthy Cities, https://greenroofs.org/about-green-roofs.
Costanzo, V., et al. “Energy Savings in Buildings or UHI Mitigation? Comparison between Green Roofs and Cool Roofs.” Energy and Buildings, Elsevier, 12 May 2015, www.sciencedirect.com/science/article/pii/S0378778815003527.
“Green Roof Benefits.” National Parks Service, U.S. Department of the Interior, https://www.nps.gov/tps/sustainability/new-technology/green-roofs/benefits.htm.
“Green Roofs and Solar Power – Biosolar Roofs Are Smart Green Infrastructure.” Livingroofs, 29 Oct. 2019, https://livingroofs.org/green-roofs-solar-power/.
Loureiro, Ana, and Susana Veloso. “Green Exercise, Health and Well-Being.” ResearchGate, Springer, Aug. 2017, https://www.researchgate.net/publication/308099577_Green_Exercise_Health_and_Well-Being.
Swain, Sunanda SwainSunanda. “Urban Heat Island Effect: Causes, Impacts and Mitigation.” Blogging Hub, 4 June 2019, www.cleantechloops.com/urban-heat- island-effect/.
“Urban Roofscapes: Using ‘Wasted’ Rooftop Real Estate to an Ecological Advantage.” Scientific American, Scientific American, 25 July 2008, https://www.scientificamerican.com/article/urban-roofscapes-ecofriendly-rooftops/.