The Science Behind Green Roofs: How They Improve Urban Environments

Are you looking for innovative ways to reduce your facility's carbon footprint? Have you considered the long-term ROI of green infrastructure but need more data to make an informed decision?

In this article, we'll provide you with the comprehensive insights you need. We'll explore the science behind green roofs, explaining how they can significantly lower energy costs, manage stormwater, improve air quality, and even enhance the well-being of your employees.

Table of Contents

• What is a Green Roof?
• How Green Roofs Regulate Temperature
• Stormwater Management
• Air Quality Improvement
• Psychological Benefits

What is a Green Roof?

A green roof, also known as a living roof, is a roof that is completely or partially covered with vegetation. At a minimum, green roofs include a waterproof membrane on which a growing medium with plants is placed, while more advanced green roofing systems may incorporate drainage and irrigation systems. 

A typical green roof consists of several layers:

Waterproof Membrane

This is the foundational layer that protects the building from water leakage.

Root Barrier

This layer prevents roots from penetrating the waterproof membrane.

Drainage Layer

This section allows excess water to drain away, preventing waterlogging.

Soil Layer

This is where the plants grow. The soil is specially engineered to be lightweight and provide the necessary nutrients.

Vegetation

The topmost layer consists of plants that are well-suited for rooftop conditions, usually drought-resistant species like sedums.

How Green Roofs Regulate Temperature

Traditional roofing materials, like asphalt, concrete, and black rubber are notorious for their heat-absorbing properties. These materials can reach temperatures as high as 190°F on a hot summer day.

Green roofs, however, can be 30–40°F cooler than conventional roofs, and can reduce heat flux (the rate of transfer of heat energy) from roof to building by 72%.

As a result, green roof systems may reduce energy use for air conditioning by up to 75%.

This cooling effect is the result of the evolved capacity of plants to cool themselves through numerous methods, including evapotranspiration (releasing water vapor through their leaves, much as humans release it through the skin in the process of sweating), and solar reflectance (reflecting solar radiation back into the atmosphere rather than absorbing it). 

Stormwater Management

Better stormwater management is a big focus of environmental sustainability. Historically, stormwater management has focused primarily on the process of channeling water from the built environment as efficiently as possible, through networks of pipes, gutters, and treatment plants.

Unfortunately, much of this old infrastructure can be overwhelmed during extreme storms, causing polluted water to overflow into the local environment and contaminate nearby streams, lakes, and oceans. 

Vegetative roofs can be a component of "green stormwater management". By retaining water, green roofs can turn it into a sustainable resource, utilizing it for plant growth and to cool the surrounding air. Water that is not used by the vegetation can be retained for a longer period of time and released slowly into gutters and drains, preventing traditional stormwater management infrastructure from being overwhelmed.

What's more, the soil acts as a natural filter, trapping pollutants which would otherwise end up in storm drains and, eventually, natural water bodies.

Air Quality Improvement

The issue of air quality in urban environments is a growing concern, especially as cities continue to expand and become more densely populated. Traditional roofing systems do little to mitigate this problem, but green roofs may be a compelling solution.

Plants are nature's air purifiers. Through the process of photosynthesis, they absorb carbon dioxide and release oxygen. This is a well-known fact, but what's less commonly understood is the plant's ability to absorb other harmful pollutants from the air. These include volatile organic compounds (VOCs), nitrogen oxides, and particulate matter. Plants capture these pollutants through their leaves and roots, effectively removing them from the air we breathe.

Traditional roofing materials like asphalt and concrete absorb and retain heat, contributing to localized temperature spikes. These elevated temperatures can exacerbate the formation of smog. Smog is essentially a cocktail of pollutants, including nitrogen oxides and volatile organic compounds, that react with sunlight to form ground-level ozone. Elevated temperatures accelerate these chemical reactions, making smog formation more likely and more intense.

By introducing vegetation, green roofs act as natural coolants, absorbing less heat and reflecting more sunlight than conventional roofing materials. This cooling effect can significantly lower local temperatures, reducing the rate of smog-forming chemical reactions.

Psychological Benefits

The concept of biophilia suggests that humans have an innate affinity for nature and natural processes. This idea, popularized by biologist E.O. Wilson, has been supported by numerous studies showing that interaction with nature can have profound effects on mental health. For instance, research has found that even brief exposure to green spaces can reduce stress, improve mood, and enhance cognitive function.

Green roofs, as accessible natural spaces in urban environments, can serve as a practical application of biophilic design, bringing these psychological benefits right to your doorstep—or rather, your rooftop.

Moreover, the visual appeal of green roofs can stimulate mental engagement and creativity. The colors, textures, and biodiversity offer sensory stimulation that can inspire and uplift. This is particularly beneficial in corporate settings, where employee well-being is closely tied to productivity and job satisfaction. Companies that invest in green roofs may find that they are not just saving on energy costs but also improving the overall work environment, leading to higher levels of employee engagement and lower turnover rates.

Green roofs can also serve as communal spaces, encouraging social interaction and community building. Social support is a significant factor in mental health, and communal green spaces offer a setting for social activities, whether it's a casual chat or organized events.

The Bottom Line

Green roofs are more than just an aesthetic choice; they're a multifaceted solution to several of today's most pressing environmental challenges. From regulating temperature and managing stormwater to improving air quality and enhancing mental well-being, the science-backed benefits of green roofs make them a compelling solution to modern problems.

If you're committed to sustainability and operational efficiency, consider taking the first step by talking to GIDEON about conducting a comprehensive roof audit. Your roof isn't just a barrier against the weather; it's an untapped resource for sustainable innovation.