roof garden

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The roof garden of the Rockefeller Center in Manhattan.

The roof terrace of the Casa Grande hotel in Santiago de Cuba.

An extreme example of a roof garden, in Vancouver, British Columbia.

It has been suggested that Rooftop farming be merged into this article or section. (Discuss)

A roof garden is any garden on the roof of a building. Besides the decorative benefit, roof plantings may provide food, temperature control, hydrological benefits, architectural enhancement, habitats or corridors^[1] for wildlife, and recreational opportunities.

History

Humans have grown plants atop structures since antiquity. An early example is in the medieval Egyptian city of Fustat, which had a number of high-rise buildings that Nasir Khusraw in the early 11th century described as rising up to 14 stories, with roof gardens on the top story complete with ox-drawn water wheels for irrigating them.^[2]

Environmental Impact

Roof gardens are found most often in urban environments. The plants reduce overall temperatures of the building which in turn reduces energy consumption. "The primary cause of heat build-up in cities is insulation, the absorption of solar radiation by roads and buildings in the city and the storage of this heat in the building material and its subsequent re-radiation. Plant surfaces however, as a result of transpiration, do not rise more than 4–5 °C above the ambient and are sometimes cooler."^[3] This then translates into a cooling of the environment between 3.6 and 11.3 degrees Celcius, depending on the area on earth (in hotter areas, the environmental temperature will cool more). The study was performed by the University of Cardiff. ^[4]

Available gardening areas in cities are often seriously lacking, which is likely the key impetus for many roof gardens. The garden may be on the roof of an autonomous building which takes care of its own water and waste. Hydroponics and other alternative methods can expand the possibilities of roof top gardening by reducing, for example, the need for soil or its tremendous weight. Plantings in containers are used extensively in roof top gardens. Planting in containers prevents added stress to the roof's waterproofing. One high-profile example of a building with a roof garden is Chicago City Hall.

For those who live in small apartments with little space, square foot gardening, or (when even less space is available) living walls (vertical gardening) can be a solution. These use much less space than traditional gardening (square foot gardening uses 20% of the space of conventional rows; ten times more produce can be generated from vertical gardens). These also encourage environmentally responsible practices, eliminating tilling, reducing or eliminating pesticides, and weeding, and encouraging the recycling of wastes through composting.

Importance to Urban Planning

Becoming green is a high priority for urban planners. The environmental and aesthetic benefits to cities is the prime motivation. It was calculated that "the temperature in Tokyo could be lowered by 0.11–0.84 °C if 50% of all available rooftop space were planted with greenery. This would lead to a savings of approximately 100 million yen per day in the city's electricity bill."^[5]

Singapore is very active in green urban development. "Roof gardens present possibilities for carrying the notions of nature and open space further in tall building development."^[6] When surveyed, 80% of Singapore residents voted for more roof gardens to be implemented in the city's plans. Recreational reasons, such as leisure and relaxation, beautifying the environment, and greenery and nature, received the most amount of votes.^[7]

Roof Garden vs. Green Roof

A roof garden is actually very different from a green roof, although the two terms are often and incorrectly used interchangeably. A roof garden is an area that is generally used for recreation, entertaining, and as an additional outdoor living space for the building's resident(s). It may include planters, plants, dining and lounging furniture, outdoor structures such as pergolas and sheds, and automated irrigation and lighting systems. A roof garden reestablishes the relationship between man and nature that can be lost in urban environments.^[8]

It is different from a green roof in that the considerations are primarily of an aesthetic and/or recreational nature, whereas a green roof is usually constructed to cover a large area in the most economical and efficient means possible with an emphasis towards improving the insulation and/or improve the overall energy efficiency of cooling and heating costs within a building.

The panels that comprise a green roof are generally no more than a few inches up to a foot in depth, since weight is an important factor when covering an entire roof surface. The plants that go into a green roof are usually sedum or other shallow-rooted plants that will tolerate the hot, dry, windy conditions that prevail on most rooftop gardens. With a green roof, "the plants layer can shield off as much as 87% of solar radiation while a bare roof receives 100% direct exposure."^[9]

The planters on a roof garden, on the other hand, can generally range anywhere from 6" up to 3' in depth, depending on the weight-bearing capacity of the roof, and would be placed more for aesthetic purposes. These planters can hold a range of ornamental plants, anything from trees, shrubs, vines, or an assortment of flowers. Since the planters on a roof garden are placed in random fashion, it would much less likely to provide the environmental and energy benefits of a green roof.

Science of Gardening

The related idea of a living machine is based on the most basic cycle of gardening: using wastes (organic waste and sewage), appropriately broken down, usually in some specialized container, on the soil, and harvesting food which, when processed, generates biodegradeable waste, and when eaten, generates sewage. In most of the world, this kind of very tight closed loop gardening is used, despite certain health risks if necessary precautions are not taken. Composting human or pet waste should achieve thermophilic conditions and age for at least a year before being used.

Composting itself is a safe process which, when composed of a variety of different materials, is one of the best forms of fertilization available.

See also

• Terrace garden
• Composting toilet
• Wildlife corridor
• Cool roofs
• Green roof
• Hanging Gardens of Babylon
• List of gardening topics
• Living wall
• Kensington Roof Gardens
• Urban agriculture
• Ralph Hancock, Designer of The Rockefeller Center Roof Gardens
• Amber Freda, Designer of New York City roof gardens

References

External links

• Greenhouse in the Sky
• Website with pictures of roof gardens in London
• Ralph Hancock website
• Amber Freda's NYC Roof Gardens