Green roof
A green roof is a roofing system that incorporates soil and vegetation atop buildings, ranging from simple grasses to elaborate gardens. Historically, green roofs have been utilized for centuries, with ancient examples like the Hanging Gardens of Babylon showcasing their benefits for insulation and aesthetics. Interest in green roofs surged during the 1970s energy crisis, leading to modern applications focused on sustainability and carbon footprint reduction.
Today, green roofs are categorized into two types: extensive and intensive. Extensive green roofs feature shallow soil and are often planted with low-growing plants, serving primarily as insulation. In contrast, intensive green roofs have deeper soil layers, accommodating a wider variety of plants, including shrubs and trees, and can create park-like spaces that benefit communities.
The environmental advantages of green roofs include reducing urban heat, managing rainwater runoff, and improving air quality. Maintenance varies based on the type and scale of the garden, with intensive roofs generally requiring more care. Interest in green roofs is expanding beyond Europe, with initiatives in cities across North America promoting their use as a sustainable architectural feature.
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Green roof
A green roof is a roof of a house, an office, or other building that is covered with soil and some form of vegetation. The vegetation can be as simple as grass or moss; it can be as involved as a vegetable garden or even a park. Green roofs have existed for centuries, since ancient people piled sod on top of their homes as a form of insulation to keep their dwellings warm in winter and cool in summer. Interest in green roofs grew in the 1970s when the energy crisis led to attempts to find ways to conserve energy. In the twenty-first century, interest in green roofs continues to grow as people concerned with conserving resources and reducing their carbon footprint seek new ways to use this old technique.
Background
No one is sure exactly how long people have used green roofs on their homes, but it is known that the Hanging Gardens of Babylon, built around 500 BCE, were essentially a green roof system. On top of stone buildings with hefty arched beams, the ancient builders added an under roof of reeds coated with tar to make them water-resistant. Soil was added to hold the many plants and even trees that were planted on top of the roof. The result was so impressive that the structure was considered one of the Seven Wonders of the Ancient World.
Other simpler forms of green roofs were used throughout the world for many centuries. These usually involved cutting chunks of grass with the roots and soil intact—known as sod—and laying these on top of a reinforced roof. In some cases, these homes were built partially into a hillside with the sod allowed to grow and blend into the surrounding ground. One culture known for these sod-covered green roof homes was the Vikings, who lived in Scandinavia in the Middle Ages. These houses were so much a part of the Viking way of life that when they voyaged to North America, they built homes with sod roofs there as well. Replicas of these homes can be seen in the historic L'Anse aux Meadows, which today is a World Heritage Site run by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) in Newfoundland.
In the 1960s and 1970s, the Germans developed an interest in green roofs that flourished as rising costs led to increased attention to ways to conserve energy. By the 2020s, it was estimated that there were about 3.1 square kilometers (1.1 million square miles) of green roofing in Germany, and that as much as 10 percent of all flat roofs in that country were green roofs. As attention to green lifestyles and a desire to reduce carbon footprints have grown, interest in green roofs has grown, too.
Overview
Most twenty-first-century green roofs fall into one of two categories: extensive or intensive. Extensive green roofs are similar to the ancient sod roofs; the roof is covered with a layer of dirt that is four inches deep and planted with shallow-root plants such as grasses, herbs, mosses, and some forms of succulents. These are generally built on homes or other private buildings and are intended to serve as insulation and improve the environment. Extensive roofs can cost about $10 a square foot and up.
Intensive green roofs are covered with a deeper layer of soil—at least six inches or deeper—and planted with a variety of plants. These can include grasses and other low-growing plants, but generally contain larger plants such as flowers, vegetable plantings, and even bushes, shrubs, and trees. These types of gardens can be park-like and are sometimes open to the community. They are often added to public buildings such as offices and are intended in part to replace the square footage of ground that is taken up by the building.
Another advantage of green roofs, especially larger intensive roofs, is reducing the overall heat in an area. Areas such as cities that have a large number of conventional roofs can help drive up the overall temperature because of a concept known as a heat island. A standard shingled or tarred roof can exceed a surface temperature of ninety degrees Fahrenheit, or about thirty-two degrees Celsius. A planted green roof is generally at air temperature or lower, helping to keep the entire area cooler by reducing the heat that is radiated from the roof and eliminating heat islands.
The maintenance required for green roofs depends on the type and size of the garden. Some small single-home roofs planted with sedums or grasses may require little or no maintenance. Others may require watering and/or pruning. Intensive gardens usually require some form of irrigation and more attention to maintenance.
Placing a green roof on an individual home offers a number of benefits. The roof can help keep the rooms underneath warmer in winter and as much as eight degrees cooler in summer, helping to reduce heating and cooling costs. They reduce the risk of problems from rainwater runoff. In many cases, a green roof will last as much as twice as long as a conventional roof. It also benefits the environment because the plants help purify the air.
While European countries, led by Germany, tend to have the greatest number of green roofs, interest has grown in North America. The Green Roofs for Healthy Cities association was formed in 1999 to promote the concept and provide information for those who are interested. Among the cities that have developed programs to promote green roofs as a result of the association's influence are New York; Chicago; Washington, DC; Portland, Oregon; and Toronto, Ontario.
Bibliography
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