Rooftop Gardens: Benefits for Energy Consumption

In cities all around the world, forgotten rooftops can change the way we conserve energy. These vast and underutilized spaces have the power to reduce energy consumption and produce food. They also have the power to provide homes for vulnerable wildlife.

All that’s required is a simple rooftop garden. By creating more green spaces in the sky, we can transform our cities with eco-friendly measures. That will benefit everyone.

What are Rooftop Gardens?

The concrete behemoths that dominate a city’s skyline often ignore the extra land space tucked out of our line of sight. With the amount of available ground-level land shrinking in urban areas, it’s more important than ever to think about how we can expand upwards.

Rooftop gardens offer a solution to our urban crisis. They are an easy, cost-effective way to reduce a building’s energy consumption while promoting a variety of other benefits.

Types of Rooftop Gardens

There are two main types of rooftop gardens: intensive and extensive.

1. Intensive Green Roof

This system uses a thick layer of soil, often several inches deep, spread across a flat roof. Sometimes, a raised garden bed may be used to cultivate a more diverse range of plants. Those can include vegetables. The large amount of nutritious soil people use there allows for larger plants and trees to flourish.

Intensive green roofs are often on commercial buildings. The structure must be sturdy enough to bear the weight. They often require more maintenance than other types of rooftop gardens.

However, they have the extra benefit of producing food right in heart of a city. If done correctly, a bland and otherwise unusable area can be revamped into a beautiful and relaxing space for residents and employees alike.

2. Extensive Green Roof

The extensive green roof system uses a lighter load of growing medium compared to the intensive system. A thin layer of soil is spread across the roof and populated by hardy species. Those can include succulents and grasses.

These low-maintenance plants grow quickly and can absorb heat. They cool the entire building in the process.

They are just a few inches thick. As a result, these mini gardens are suitable for a variety of different rooftops, like slanted suburban homes (and, yes – earthships).

Extensive green roofs can be aesthetically impressive. They cover unsightly concrete with unique vegetative designs.

The drought-resistant plants can survive even the worst weather. They are a great option for smaller residential buildings looking to cut down on their energy bill.

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How Rooftop Gardens Conserve Energy

Rooftop gardens employ some of the best insulation around: soil and vegetation. From the tropical jungles of South America to the coniferous forests of Europe, vegetation has always provided a natural refuge from the heat. The tree cover and thick underbrush protects against the harsh sun, allowing for the underneath to stay cool and breezy.

Hot, sunny days can cause the tops of buildings to reach mind boggling numbers, even as high as 150 degrees F. Without an insulating layer, this heat will naturally pass through the building as its concrete exterior acts as a conductor.

Air conditioning systems must be used to regulate the temperature, causing an unnecessary expenditure of money, energy and resources. In hot climates, it’s not uncommon for residents to spend 70% of their electricity bill on cooling costs.

Rooftop gardens are incredibly effective insulation systems and can help to lower the cost of cooling a building. While soil naturally functions as an insulator, the plants on top can also drop the temperature through photosynthesis and transpiration.

These natural processes are why the shade of a tree often feels 2–9°F cooler than shade created by a roof or structure on a blistering day.

When water is added to the equation, the cooling effect is twofold. Moist soil naturally cools as water evaporates from it, refrigerating the surface below.

While this process is especially beneficial in the summer, rooftop gardens can also keep the building from losing heat in winter. A layer of insulation on roofs is useful in most weather conditions, keeping temperatures stable in buildings and protecting it from extreme and harsh weather conditions.

The Heat Island Effect

Traditional rooftops have materials that absorb large volumes of heat that the sun radiates. In urban areas, the density of buildings creates pockets of warmth called “heat islands”, which can spike the surrounding air temperature.

On average, cities are hotter that the open countryside. With large cement structures absorbing heat and obstructing the natural cooling process, the difference in temperature can be as high as 1.8–5.4°F during the day and a whopping 22°F in the evening.

City dwellers end up using a considerable amount of energy to cool down their homes, producing more emissions than their rural neighbors.

Covering urban rooftops with greenspaces would be a great solution for the heat island effect. Not only would these rooftop gardens lower the temperature, but they also work in removing harmful pollutants from the air through natural filtration systems. Urban jungles can make our work and living spaces healthier for our bodies and the environment.

Saving Money and Energy

The amount of money saved is largely down to climate and, of course, electricity consumption. In more temperate climates, the savings will not be as much as those living in more extreme temperatures as heaters and air conditioners are rarely used. However, regardless of the weather, rooftop gardens can help to reduce energy expenditures overall.

One study found that the amount of energy saved in the summer by Canadian buildings with rooftop gardens to be 20% for the upper floor. This translates into a 6% decrease of energy consumption for the entire building if it is five or more floors, and 10 – 12% if the building only consists of two floors.

In fact, the city of Toronto has estimated that it could save an approximate $22 million if it had to implement a full-scale city initiative.

The savings accrued by buildings in more extreme weather systems can be far greater. Another study found that green-roofed homes in the Middle East reduced their energy consumption by 24%-35% on average.

In climates with extremely hot temperatures, 70% of energy is spent on air conditioning systems. By implementing a simple rooftop garden, buildings could save as much as 50% on their average electricity expenditure.

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The History of Rooftop Gardens

Historically, green roofs have been the norm in many Scandinavian cultures. In the past, a layer of turf was used to cover the roofs of homes, churches and other small buildings. These systems are often referred to as “sod roofs” and were commonplace up until the 18th century.

People living in northern countries during this period understood the benefits of padding their roofs with nature. The layer of soil and vegetation on the roof insulated their homes, protecting them from the harsh snow in winter and heat of sweltering summer days.

The system must have been quite effective if you consider how labor-intensive it was to create a sod roof without the use of modern-day tools.

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The Extra Benefits of Green Roofs

Beyond the insulating effects of rooftop gardens, utilizing concrete slabs to create green spaces comes with a whole host of benefits. With urbanization slowly encroaching on natural habitats and landscapes, vast regions have been stripped of their natural ecosystems.

This has had a devastating effect on pollution, wildlife populations, and our collective mental health. By reintroducing nature, we can help to reverse some of the more damaging aspects of urban sprawl.

1. Reduces CO2 Emissions

A city littered with green roofs would do wonders in reducing the total amount of CO2 escaping these areas. Rooftop gardens can absorb CO2 from the air and release oxygen in its place, creating a healthier urban environment.

Currently, CO2 emissions are the largest contributor to greenhouse gases released by humans. If we installed green roofs, we would be able to reduce this percentage while still conserving energy.

A study in Michigan estimated that if every rooftop in Detroit had greenery, these roofs would have the ability to remove the same amount of CO2 produced by 10,000 trucks over the course of two years.

This is also carbon that is being absorbed in the areas that need it the most, as cities have far less vegetation and produce far more CO2 on average than surrounding regions.

2. Provides a Habitat for Wildlife

The destruction and clearing of large swaths of natural habitats for urban development has displaced many creatures. Rooftop gardens offer nesting areas and homes for insects, which attracts a range of birds. Flowering plants on roofs provide very necessary food and habitats for bees, which have been in desperate need of help recently.

We shouldn’t underestimate the ecological value of these rooftops, as a report noted that  37 species of birds were on just ten rooftop gardens in New York. This population of birds included some uncommon species, such as woodcocks, magnolia warblers, flycatchers, falcons and hummingbirds. These birds do not usually live in cities, although they’re an essential part of the ecosystem.

3. Allows for Better Storm Water Management

Rooftop gardens trap water and slow its descent to road-level surfaces, thereby helping cities manage the huge amounts of water passing over them during severe storms. Green roofs have been found to reduce water run-off by an average of 50%, allowing cities to retain healthy amounts of water that can keep them cool when the sun comes out again.

When several major city buildings implement green roofs, it greatly relieves the pressure of the storm water drainage systems that are already dealing with the brunt of climate change and its resulting super storms.

4. Can Produce Food

Rooftop gardens have the ability to produce food right where the demand for it is at its highest: in densely populated cities. Growing food in the center of a city reduces transportation costs. That’s because customers are in the direct vicinity of the farm.

It also results in a smaller carbon footprint. People then don’t need trucks to deliver food from outside areas.

The food produced on these rooftops is often more nutritious than other food on the plate. That’s due to its freshness and the lack of processing people need to do to preserve it.

Vegetables lose their nutritional value rather quickly after being people harvest them. This number is far higher than most would expect. Spinach can lose over 50% of its vitamin C content by the time it reaches someone’s plate.

Cultivating crops on rooftops also reduces the need to create new farmlands through forest clearing, which has a significant impact on environmental degradation and global warming. Luckily, we as humans have a diverse range of edible species at our disposal that we can grow in a range of climates on rooftops.

Those need relatively little maintenance. This type of rooftop food production not only has a smaller carbon footprint than other foods, but it can often be “carbon negative” as it also reduces energy expenditures.

5. Can Boost our Mood

Green spaces in cities may significantly reduce overall stress in a population. A hypothetical city that has green roofs full of chirping birds, beautiful foliage and healthy food could do this even more effectively.

A rooftop garden offers a refreshing reprieve for employees and residents who live in constricted, industrial spaces with little access to nature.

We can’t underestimate the effects of these green spaces. In one study, people that grew up in areas with few green spaces had a 55% higher chance of developing mental disorders, such as anxiety, depression and substance abuse, than those living in natural environments. This lessens the burden of healthcare costs as fewer individuals rely on costly pharmaceuticals or doctor visits.

Rooftop gardens not only reduce stress and incidents of mental strain, but they actually increase productivity. Offices that include a considerable amount greenery have been found to boost the productivity of employees by up to 15%. A city that is 15% more productive as a whole would have huge economic and social benefits, leading to a happier and healthier life for all.

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