A roof garden is a garden built on the top of a building. In addition to looking nice, plants on rooftops can provide food, help control temperature, improve water management, enhance building design, create homes or paths for animals, offer places for people to relax, and in large areas, may help the environment. Growing food on building rooftops is sometimes called rooftop farming. This is usually done using green roofs, hydroponics, aeroponics, air-dynaponics, or container gardens.

History

People have grown plants on top of buildings since ancient times. In Mesopotamia, which was around 4,000 to 600 years ago, ziggurats had trees and shrubs on raised platforms. In ancient Rome, the Villa of the Mysteries in Pompeii had a raised area where plants were grown. A roof garden was also found near an audience hall in Caesarea during the Roman-Byzantine period. In the medieval Egyptian city of Fustat, buildings described by Nasir Khusraw in the early 11th century reached up to 14 stories. These buildings had roof gardens on the top floor, with water wheels pulled by oxen to help water the plants.

The Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World, are often shown as tall buildings covered with plants, including large trees.

Between 1880 and the start of Prohibition, New York City had many rooftop gardens. Examples include the Hotel Astor, the American Theater on Eighth Avenue, the garden on Stanford White’s 1890 Madison Square Garden, and the Paradise Roof Garden opened by Oscar Hammerstein I in 1900. These rooftop gardens were popular places for concerts, vaudeville shows, and ballroom dancing until the 1920s.

Commercial greenhouses on rooftops existed as early as 1969, when Terrestris rooftop nursery opened on 60th Street in New York City. In the 2010s, large commercial hydroponic rooftop farms were started by companies like Gotham Greens and Lufa Farms.

Environmental impact

Roof gardens are commonly found in cities. Plants on these roofs help lower the amount of heat absorbed by buildings, which reduces the need for cooling energy. "The main reason cities get hot is because sunlight is absorbed by roads and buildings, and this heat is stored in materials and later released. However, plants release water vapor through a process called transpiration, which keeps their surfaces only 4–5 °C (7–9 °F) warmer than the surrounding air, sometimes even cooler." This helps cool the environment by 3.6–11.3 °C (6.5–20.3 °F), depending on the location (cooler areas see less of a temperature drop). This study was conducted by the University of Cardiff.

A study by the National Research Council of Canada compared roofs with gardens to those without gardens, showing how temperature affects each type of roof at different times of the day. The study found that roof gardens significantly reduce temperature effects compared to roofs without gardens. "If used widely, rooftop gardens could reduce the urban heat island effect, which would lower smog, heat-related health problems, and energy use for cooling."

In addition to reducing heat, roof gardens also help manage rainwater. They slow down water runoff, reduce how much water flows off roofs, and lower the total amount of runoff. "As cities grow, natural materials like soil are replaced by solid structures such as buildings and roads. This causes problems with stormwater runoff and sewage overflows in many North American cities. A key solution is to reduce the speed of water flow by delaying runoff (e.g., using controlled drains on roofs) or storing it (e.g., using rain basins). Rooftop gardens can slow down water flow and store runoff for plants to use later."

Urban agriculture

Rooftop gardens can be used for small-scale farming in cities, helping to grow food locally. These gardens can provide fresh food for communities and show people how food is produced. At Trent University, there is a working rooftop garden that supplies food to the student café and nearby residents.

City areas often have few places for gardening, which is why many buildings have rooftop gardens. Some rooftop gardens are on buildings that handle their own water and waste. Methods like hydroponics can help grow plants without soil, which reduces weight and makes rooftop gardening easier. Plants in containers are commonly used in rooftop gardens because they protect the roof's waterproofing. A well-known example of a building with a rooftop garden is Chicago City Hall.

People living in small apartments with limited space can use square foot gardening or vertical gardens (green walls) to grow plants. These methods use much less space than traditional gardening.

Importance to urban planning

Becoming green is an important goal for city planners. The main reason is the benefits to the environment and the appearance of cities. Studies show that if 50% of all rooftops in Tokyo were covered with plants, the temperature could drop by 0.11–0.84 °C (0.20–1.51 °F). This change could save about 100 million yen in costs.

Singapore is working hard to develop green cities. Roof gardens offer a way to bring nature and open space into tall buildings. A survey found that 80% of Singapore residents support adding more roof gardens to the city. Most people voted for reasons like relaxation, beauty, and enjoying greenery. Planting gardens on building tops helps cities become more efficient.

A roof garden is different from a green roof, though the terms are often used the same way. Roof gardens are designed for recreation, such as entertaining, dining, or relaxing. They may include planters, plants, furniture, structures like pergolas, and systems for watering and lighting.

A green roof does not always focus on recreation. It may not have space for people to use and is built mainly to improve a building’s insulation or reduce energy costs for heating and cooling.

Green roofs can be extensive or intensive. These terms describe the type of plants used. The materials on a green roof are usually no more than a few centimeters to 30 cm (a few inches to a foot) deep because weight is important when covering a roof. Plants like sedum or other shallow-rooted species are used because they can survive hot, dry, and windy conditions. These plants can block up to 87% of solar radiation, while a bare roof receives 100% of the sun’s heat.

Planters on roof gardens can be made for many purposes and vary in depth to meet aesthetic or recreational needs. They may hold trees, shrubs, vines, or flowers. However, because aesthetics and recreation are the focus, these planters may not offer the same environmental or energy benefits as green roofs.

In popular culture

• American jazz singer Al Jarreau wrote a song called "Roof Garden," which was on his 1981 album.
• Apu Nahasapeemapetilon from the TV show The Simpsons has a rooftop garden that Paul McCartney and his wife visited.
• In BBC's 1990 television miniseries House of Cards, the main character, Member of Parliament (MP) Francis Urquhart, murders journalist Mattie Storin by throwing her from the Palace of Westminster's rooftop garden.

Gallery

• Villa Arson
• Villa Arson
• ACROS Fukuoka
• Herb garden at the National Museum of Nature and Science in Tokyo
• A small Zen-style roof garden
• Sedum roof at Urban Deli in Stockholm
• Rooftop community gardens are a common feature in solarpunk art
• Inari Daimyojin statue on the roof of Hankyu Department Stores Umeda main store
• Tokyo Plaza
• Canal City Hakata
• F-Roof: a multi-purpose roof that produces food and energy and has no tiles behind it in Cugir, Romania.