Green roof

A green roof or living roof is a special kind of roof on a building. Instead of being made just of concrete or metal, it is covered with plants and soil, placed over a special waterproofing membrane. This helps keep the water out and protects the building. Green roofs might also have extra layers, like a root barrier, drainage systems, and even irrigation to help the plants grow.

Green roofs are helpful in many ways. They can catch and absorb rainwater, which helps prevent flooding. They also act like insulation, keeping the building cooler in summer and warmer in winter. These roofs give a nice, pretty look that can make people feel happier. They also give wildlife a place to live and help cool down hot city air, lessening something called the heat island effect.

There are mainly two types of green roofs. One type, called an intensive roof, is thicker and can hold many kinds of plants, but it is heavier and needs more care. The other type, an extensive roof, is thinner and lighter, needing very little care. Both types help make cities cleaner and more pleasant places to live. Sometimes, the word "green roof" is also used for roofs that have special green technology, like solar thermal collectors or photovoltaic panels.

Environmental benefits

Thermal reduction and energy conservation

Green roofs help save energy and keep buildings cooler. They can make buildings warmer in winter and cooler in summer by adding layers that keep heat in or out. This also helps cities stay cooler during hot weather. Studies show that adding green roofs can make a whole city a little bit cooler.

Green roofs can cut down how much cooling a building needs by a lot, especially if they are covered to trap heat. In cities, green roofs can help lower temperatures during summer.

Water management

Green roofs help manage water by holding onto rainwater. The soil and plants take in water and slowly release it back into the air. This means less water runs off quickly from the roof. Green roofs can keep a lot of rainwater and help keep pollutants out of waterways.

Ecological benefits

Green roofs give animals like birds, bees, and butterflies a place to live even in busy cities. They also help clean the air by taking in harmful substances.

Carbon sequestration

Green roofs can also help the environment by storing carbon, which is found in plants and soil. This helps reduce the amount of carbon dioxide in the air. The plants and soil in green roofs keep carbon inside them, helping to fight climate change.

Other

Green roofs can also help block sounds, earn special points for green building standards, provide space for growing food, and keep the temperature of rainwater balanced.

Costs and financial benefits

A well-built green roof can cost between $108 and $248 for every square meter, or $10 to $23 for every square foot for a simple design. A more complex green roof can cost between $355 and $2,368 for every square meter, or $33 to $220 for every square foot. However, since many materials can be reused, replacing a green roof usually costs about one-third of the original price.

There are many benefits to having a green roof. It can make a roof last much longer by protecting it from harmful sunlight and damage. It can also raise the value of a house by about 7%. Green roofs help save energy by keeping buildings warmer in winter and cooler in summer. This can lower the energy needed to heat and cool a building, saving money all year. Some places even offer tax breaks or other rewards for adding green roofs, especially in areas with problems like too much stormwater or very hot temperatures. For example, New York City offers a tax credit for owners who green at least half of their roof.

Disadvantages

Green roofs can be more expensive to install than regular roofs, sometimes costing twice as much. They also need more care, like cleaning and checking for weeds. Because they hold water, the roof’s waterproofing must be very strong to keep water out.

The extra weight from soil and water can be a problem for buildings. Not all buildings can support this weight, which makes it hard to add green roofs to many places. In some areas where the ground shakes, special strong building rules are needed. Sadly, the weight once caused a big roof to collapse.

Green roofs also need more energy for things like watering plants, especially when it doesn’t rain much. Making the materials for green roofs can also create more carbon dioxide than regular roofs. When green roofs are old and need to be replaced, rules about what to do with the old materials are not yet clear.

Types

Green roofs can be divided into different types based on how deep the soil is and how much care they need. Some green roofs need a lot of care and have deeper soil to grow bigger plants, like shrubs or small trees. These are called intensive green roofs. Others need very little care and have a thin layer of soil, often just enough for small plants like Sedum and mosses. These are called extensive green roofs.

Some green roofs mix features of both types, and there are also special designs for roofs with a slope, like those found in Scandinavian buildings.

History

Long ago, green roofs were made from natural materials like earth and plants, often used for growing food or building homes. These early roofs helped protect people from bad weather and kept homes cool in summer and warm in winter. But they were not good at keeping water out or stopping animals from getting in.

Today’s green roofs are made with special layers designed to support plants and soil. They began in Germany in the 1960s and have become popular in many places. Countries like Germany, Switzerland, and the Netherlands have groups that help people build green roofs. Some cities even give money to developers who use them. In North America, cities such as Toronto and San Francisco require new buildings to have green roofs. Scientists study green roofs to learn how they can help cool down busy city areas.

Brown roofs

Industrial areas can be important homes for rare plants, animals, and insects. As these areas are often rebuilt, these special homes are lost. "Brown roofs," also called "biodiverse roofs," help by covering flat roofs of new buildings with local materials like rubble or soil. This gives nature a place to grow.

These roofs can attract spiders, insects, and birds. One famous brown roof is at Laban, a dance center in London, designed to help rare birds. Another is on the Barclays Bank HQ in Canary Wharf, London, which is very high up and serves as a nature reserve.

Blue-Green Roofs

Blue roofs help manage rainwater by storing it and controlling how quickly it flows away. A blue-green roof mixes this idea with a green roof, storing water under layers of soil and plants. This helps reduce rainwater running off too quickly, reuse water for watering plants, and keep buildings cooler inside.

Blue-green roofs are great for saving energy because the water layer keeps temperatures steady. They are helpful all year, staying cooler in summer and less affected by temperature changes in winter compared to regular roofs. They also evaporate more water, which keeps surfaces cooler and helps reduce heat in cities.

ASLA Award Green Roof Projects

• 2017 Award: Seeding Green Roofs for Greater Biodiversity and Lower Costs, Lincoln, NE, USA. Richard Sutton
• 2013 Award: Green Roof Innovation Testing Laboratory, Toronto, Ontario, Canada. John H. Daniels, Brooklyn Botanic Garden Visitors Center, Brooklyn. HMWhite, and NYC Parks Green Roof: A Living Laboratory for Innovative Green Roof Design, New York, NY. NYC Parks
• 2012 Award: Lafayette Greens: Urban Agriculture, Urban Fabric, Urban Sustainability, Detroit. Kenneth Weikal Landscape Architecture 200 Fifth Avenue, NYC. Landworks Studio, Inc.
• 2011 Award: Manassas Park Elementary School Landscape, Manassas Park, VA. Siteworks
• 2009 Award: California Academy of Sciences, San Francisco, CA. SWA Group, Changi Airport Terminal 3 Interior Landscape, Singapore. Tierra Design (S) Pte Ltd, Corporate Headquarters, San Francisco, CA. OLIN, Macallen Building, South Boston, MA. Landworks Studio, Inc., and Museo del Acero Horno3, Monterrey, Mexico. Surfacedesign Inc.+ Harari arquitectos
• 2008 Award: Gannett/USA Today Headquarters, McLean, Virginia. Michael Vergason Landscape Architects, Ltd.
• 2007 Award: Washington Mutual Center Roof Garden, Seattle, Washington. Phillips Farevaag Smallenberg
• 2002 Award: Chicago City Hall Green Roof, Chicago, Illinois. David Yocca

Examples by country

Australia

Green roofs have become more popular in Australia in the last ten years. Early examples include the Freshwater Place residential tower in Melbourne (2002) with its Level 10 rooftop Half Acre Garden, the CH2 building housing the Melbourne City Council (2006) – Australia’s first 6-star Green Star Design commercial office building, and Condor Tower (2005) with a lawn on the 4th floor.

Since 2008, city councils and business groups in Australia have promoted the benefits of green roofs. "The Blueprint to Green Roof Melbourne" is a program run by the Committee for Melbourne. In 2010, the largest Australian green roof project was announced. The Victorian Desalination Project will have a “living tapestry” of 98,000 Australian indigenous plants over a roof area spanning more than 26,000 m² (280,000 square feet). The roof will blend the building into the landscape and provide benefits like acoustic protection and reduced maintenance.

In June 2014, ecological artist Lloyd Godman, with structural engineer Stuart Jones and environmental scientist Grant Harris, installed an experiment using special plants at levels 92, 91, 65 and 56 on Eureka Tower in Melbourne, Australia. These plants grow without soil or watering and have been checked regularly since installation. One type of plant has grown from a single piece to several thriving groups.

Canada

The city of Toronto approved a rule in May 2009 requiring green roofs on certain residential and industrial buildings. By January 31, 2011, industrial buildings needed to make 10% or 2,000 m² (22,000 sq ft) of their roofs green. Toronto City Hall’s Podium roof was renovated to include a large rooftop garden, opened to the public in June 2010. Many green roofs in Canada also use practices to collect and reuse rainwater.

In 2008, the Vancouver Convention Centre installed a large living roof on its West building, making it the largest green roof in Canada. The new Canadian War Museum in Ottawa, opened in 2005, also features a grass-covered roof.

During the renovation of Hamilton City Hall in Hamilton, Ontario from 2007 to 2010, efforts were made to make the structure more environmentally friendly, including adding a grass-covered roof.

Simon Fraser University’s Burnaby campus contains many green roofs.

Canada’s first LEED Platinum V4 Home in Wakefield QC, EcoHome’s Edelweiss House, has a living Green Roof sloped at 12 degrees.

Costa Rica

Living green roofs have been built and grown at Saint Michael's Sustainable Community since 2012. Native plants, mostly flowers, provide a colorful and functional living roof. The community has the largest number of green roofs in the country.

Egypt

In Egypt, plants are grown on roofs using a method that doesn’t require soil. This eliminates the need for an insulating layer. Vegetables and fruit are popular, providing fresh, healthy food free from harmful chemicals.

An advanced method being tested in Egypt is farming fish next to plants in a closed cycle. This helps plants grow better by using fish waste and keeps the water clean by using plants.

Finland

In Finland, green roofs are still uncommon. Some experimental green roofs have been built in big cities. However, the capital city of Helsinki has published guidelines to encourage green roofs. Research is ongoing because conditions in southern Europe differ from those in colder northern climates.

France

In France, a large green roof has been created on the International School in Lyon. Another large green roof has been added to the new museum L'Historial de la Vendée which opened in June 2006.

Germany

Germany has a long history with green roofs, dating back more than 100 years. In the 1970s, green roof technology advanced significantly. Modern green roof technology was perfected in Stuttgart and implemented widely by the early 2000s. Germany has laws requiring green roofs in many metropolitan areas.

Today, about 10,000,000 m² (110,000,000 square feet) of new green roofs are constructed each year in Germany. The cities with the most green roofs are Berlin and Stuttgart. Green roofs are part of the training for landscaping professionals in Germany.

Greece

The Greek Ministry of Finance installed a green roof on the Treasury in Constitution Square in Athens. Studies showed that this roof significantly improved the building’s energy efficiency, saving money on heating and cooling. The roof also attracted beneficial insects like butterflies and bees, improving the local environment.

Iceland

Traditionally, houses and buildings in Iceland often had roofs covered with grass and plants, known as sod roofs.

India

In Kashmir, traditional houses had roofs covered with birch wood and a layer of soil where flowers and crops grew, providing insulation during winter.

Malaysia

Bus stops in Kuala Lumpur were fitted with green roofs in 2019.

Norway

Houses in Norway have had roofs covered with grass and greenery since the Viking and Middle Ages. This provided insulation during cold winters. A modern movement has revived this tradition for holiday homes and mountain lodges. Norway is also developing blue-green roof technologies to manage heavy rain events.

Poland

Several cities in Poland, including Warsaw, Krakow, and Wroclaw, have policies to encourage green roofs. The University of Warsaw has one of the largest and most well-known green roofs, covering about 10,000 square meters with over 30,000 plants.

Qatar

The Ministry of Municipality and The Public Works Authority in Doha, Qatar holds the record for the largest green roof, covering 4,031 square meters (43,389 square feet) as of September 2023.

Singapore

Singapore installed green roofs on 10 public buses in 2019 as part of an experiment. Green roofs on bus stops in Singapore were found to reduce temperatures by up to 2°C.

Switzerland

Switzerland has one of Europe’s oldest green roofs, created in 1914 at the Moos lake water-treatment plant in Wollishofen, Zürich. A meadow developed from seeds in the soil and is now a haven for many plant species.

Sweden

What is claimed to be the world’s first green roof botanical garden was set up in Augustenborg, Malmö in May 1999. The International Green Roof Institute opened to the public in April 2001. Green roofs are well-established in Malmö, with many buildings incorporating them. The Bo01 urban residential development and the Emporia shopping mall feature large green roofs.

United Kingdom

In the United Kingdom, green roofs have been used more frequently in recent years. Notable examples include the Kensington Roof Gardens in London, the University of Nottingham Jubilee Campus, and various buildings in London such as Sainsbury’s Millennium Store, the Horniman Museum, and Canary Wharf. The Ethelred Estate in London is one of the largest roof-greening projects. Toxteth in Liverpool is also a candidate for a major roof-greening project.

The University of Sheffield has a Green Roof Centre of Excellence and has conducted research into green roofs. Fort Dunlop has the largest green roof in the UK since its redevelopment between 2004 and 2006.

The UK also has innovative food preparation facilities, like the Kanes salad factory in Evesham, topped with a wildflower roof.

United States

One of the largest green roofs is found at Ford Motor Company’s River Rouge Plant in Dearborn, Michigan, covering 450,000 square feet of assembly plant roofs. Chicago’s Millennium Park has a 24.5-acre intensive green roof. Other well-known examples include Chicago City Hall and the former Gap headquarters, now YouTube’s headquarters, in San Bruno, CA. The U.S. military has major green roofs at the U.S. Coast Guard headquarters and the Pentagon.

An early green-roofed building is the Weyerhaeuser Corporate Headquarters in Federal Way, Washington, completed in 1971. The largest green roof in New York City was installed atop the United States Postal Service’s Morgan Processing and Distribution Center in Midtown Manhattan.

Atop Chicago City Hall, roof gardens were completed in 2001, serving as a pilot project to study the impact of green roofs. The garden includes 20,000 plants of more than 150 species.

The largest residential green roof in New York is at Zeckendorf Towers, transformed in 2010 as part of Mayor Michael Bloomberg’s NYC Green Infrastructure campaign.

With the passage of Denver’s Green Roof Initiative in November 2017, new or existing buildings meeting certain thresholds are required to have rooftop gardens.

Seattle has used green roofs increasingly, encouraged by city building codes. The Seattle Green Factor program rewards landscaping in new developments to reduce stormwater runoff and create habitats. By 2010, Seattle had about 8.25 acres of green roofs.

Seattle City Hall has a green roof project with over 22,000 pots of plants, aiming to reduce stormwater runoff by 50 to 75 percent.

Washington, D.C.

Washington, D.C., began offering incentives for green roofs in the early 2000s. Programs like the Riversmart Rewards Program provide subsidies for green roof projects. Rebates of $10-$15 per square foot are available for installing green roofs to reduce stormwater runoff. There is no size limit on qualifying properties. By 2020, there were 5.1 million square feet of green roofing in the district.