The Top 10 Social and Environmental Benefits of Living Green Roofs in Urban Areas

Green roofs, living roofs, vegetated roofs or eco-roofs have existed for thousands of years [1]. The Hanging Gardens of Babylon, one of the Seven Wonders of the World, used an elaborate irrigation system to create a terraced garden paradise outside of modern-day Baghdad while Europeans once used traditional sod roofs as a means of insulating houses.

Modern cities are places that are generally filled with concrete and other built structures. When one thinks of a city, nature doesn’t typically come to mind. However, with green roofs, roofs on buildings that contain living plants, nature is returning to cities in a number of new and innovative ways.

Because green roofs have a variety of benefits in urban areas, they are being built in many large cities around the world today and are a great innovation of our time.

How do green roofs work?

A living green roof allows for the growth of vegetation. Such roof consists of components like a waterproofing layer, a root barrier, a drainage system and growing medium for the plants [1].

Green roofs are also relatively easy to construct and can be fitted to most buildings with a relatively flat roof. More specifically, they work best when there is less than 20 to 30 degrees of slope [2].

You should keep in mind that the roof needs to be able to take the weight of a full garden. This is not only the dry weight of the garden but the additional weight of any rainfall or irrigation activities. Most roofs should be able to withstand this weight but conducting an expert survey is advisable.

Installation of a green roof

If you are looking to install a green roof, you may wish to first install a protection board that covers your normal roof. A layer of waterproof membrane is placed on top, followed by a layer of soil and on top of that the preferred vegetation is planted.

Some roofs, called extensive roofs, have a thinner layer of soil and are best suited for plants with shallow roots such as mosses and sedum. Other roofs, called intensive roof gardens, have a deeper layer of soil or other growing medium and so can sustain hardier plants including trees with stronger roots.

The waterproof membrane is normally made from a material such as ethylene propylene diene monomer, a rubbery material similar to the lining put down when you build something like a duck pond in the garden. This layer prevents water getting in but also stops roots from the plants growing down into the roof. There is also a possibility of adding a further insulation layer that can be placed either on the roof beams or above the waterproof layer [2,3].

To effectively maintain and water your garden, a filter layer, a drainage layer and a water retention layer are placed. These various layers also help ensure that the soil is not washed away. On top of that, a mix of porous material and soil is placed which is the growing layer.

Installers of green roofs rarely use soil as the growing medium because it is heavy and packs tight after repeated rains, reducing water retention and aeration for plant roots. Instead, manufactured materials such as granulated clay or shale are commonly applied. Organic compost and fertilizer is added as nutrients [4].

Lastly, the selection of plants will depend on whether you opt of an intensive or an extensive green roof.

A green roof maintenance

Maintaining your green roof is no different to maintaining your garden. Extensive green roofs are easier to maintain compared to intensive ones, but they all need weeding and cutting.

This is why it is important to ensure that there is safe and easy access to the green roof. What is more, you can choose to cover either the entire roof or just a part of it.

The green roof advantages for you and the urban environment

The following list shows some of the main benefits that green roofs can provide to urban areas and their inhabitants.

#1 Green roofs save energy

Conventional roofs are a large source of building heat loss in the winter and heat gain in the summer. Because green roofs help to insulate buildings, they also help to reduce building energy demands and their associated energy costs for heating and cooling.

To compare how much energy is required by a building with a green roof with buildings that have dark roofs or white (reflective) roofs, check out the Green Roof Energy Calculator from Arizona State University.

#2 Green roofs reduce stormwater runoff

Rainwater is stored by the green roof substrate and then is used by plants. The plants then undergo transpiration and respiration, where the water is released into the atmosphere as water vapor. Any small amount of rainwater that is not absorbed gets filtered by the plants before it runs off the roof.

When rainwater flows through green roofs, the green roof reduces and slows down the flow of stormwater, assisting with stormwater management problems that are common in cities.

#3 Green roofs help to reduce the urban heat island effect

The urban heat island effect occurs when the temperatures in cities increase more than the temperatures in surrounding rural areas. This difference in temperature is due to the reduced vegetation in cities and the presence of large amounts of concrete and other impervious urban surfaces that collect and radiate high amounts of solar heat during the summer.

Because plants undergo dew and evaporation on a daily basis, plants on green roofs and other urban outdoor surfaces can help to cool cities and reduce the excessive heat that accumulates in cities due to the large amounts of concrete. Plants also absorb sunlight that would otherwise be converted into heat.

#4 Green roofs are great places to grow a community garden or an urban farm

Many cities are now realizing the benefits of using previously underutilized space as a place to grow edible plants.

Many restaurants are even getting in the action by growing produce right on their own roof, giving their chefs the freshest ingredients available. Some green roofs even house beehives!

#5 Green roofs provide opportunities to increase the presence of nature in cities

In most urban environments, available habitat for wildlife is greatly reduced when compared to many rural areas that contain more of their natural habitat.

Vegetative roofs can provide habitat for birds and insects and act as “stepping stone habitats” between the isolated habitat patches that exist in the middle of cities. While many green roofs are similar to a more natural type of lawn in appearance, some green roofs even have trees and shrubs, like this one in Toronto, Canada, where birds could potentially live.

Further to adding green to our cities and other urbanized areas, another type of roof is now also beginning to provide shelter to wildlife such as birds and insects. These types of roofs are called biodiverse or brown roofs and work in a similar way to green roofs but have individual characteristics that attract certain fauna and might include sand, stones and specific plants.

#6 Green roofs have aesthetic benefits

Green roofs and other urban green spaces add beauty and charm to the built environment of cities.

#7 Green roofs improve air quality

Plants on green roofs and plants that are present on other surfaces can capture pollutants from the urban air and filter out gases from the air that could potentially be toxic to the environment and human health. Green roofs can also help to reduce dust, particulate matter, and smog in the city air.

Also, because green roofs help to moderate the temperature of both buildings and of the overall urban area, there is reduced energy demand, and therefore helps to reduce the overall amount of pollutants generated by power plants, including greenhouse gas emissions.

#8 Green roofs increase the usable spaces in cities without increasing the urban footprint

Green roofs can be used to add usable space to a building, and can provide community value, such as through recreational spaces like parks, community gardens, or commercial spaces like display areas and restaurant terraces.

#9 Green roofs create local jobs

When green roofs are being built and maintained in cities, new opportunities arise in order to meet the demand of green roof-specific manufacturing, the production and growth of plants for the roofs, and for green roof design and maintenance.

These opportunities require qualified people to work and meet that demand, thereby creating an entire new industry and the many associated jobs that go with it.

#10 Green roofs increase the lifespan of roof materials

On a green roof, the vegetation helps to reduce the exposure of the underlying roof materials to fluctuations in weather and temperature, as well as UV radiation from the sun, which can lead to wear and tear and damage to roof materials over time.