Green roofs come in many different shapes and forms, and their history goes back to time immemorial. In cold parts of the world, such as Scandinavia, sod roofs with plants growing on them were an important part of the house´s insulation for small homes.
Today, green roofs are still hailed for their insulative properties, but also as a way of creating green spaces in densely built-up cities and prevent the formation of ”concrete deserts”. The insulative properties of the green roof help protect the building against both heat and cold, and can therefore reduce costs for heating and cooling. In urban environments, green roofs can reduce flooding problems since they catch water. (Unlike asphalt and similar materials.) Green roofs are also being studied for their ability to help fight the results of the urban heat island effect.
Green roofs can be used to grow food, as recreational spaces and to provide much-needed environments for wild animals such as insects, spiders, birds and reptiles. Some green roofs are inviting for humans, while others are designed to create a more wild space, e.g. a sloped roof planted with hardy succulents that require minimal maintenance.
Green roofs, sometimes in combination with green walls, are increasingly used to ”hide” buildings or change their visual appeal. A green building can either blend in better with its likewise green surroundings, or provide much longed for contrasts against grey humdrum structures.
Growing food on the roof
Food gardens and roof-top farming has become increasingly popular in recent years and many different methods are currently being explored, from the more traditional raised vegetable beds to green-houses for microgreens. Hydroponic, aquaponic and aeroponic farming is definitely possible on roofs. Over all, container gardening protects the roof from the roots, and is therefore common for growing plants that form big roots.
What is an extensive vegetated roof?
Landscape architects distinguish between two main types of green roofs:
– Intensive vegetated roof
– Extensive vegetated roof
Roof gardens, roof farms and similar usually belong to the category intensive vegetated roof, while the standard extensive vegetated roof is planted with low plants (such as grasses and small succulents) and can be either flat or sloping. Extensive vegetated roofs tend to require less maintenance and are normally planted for other reasons than to provide humans with food or a recreational space. Extensive vegetated roofs is a lower-maintenance way of providing thermal regulation for the building, reducing the risk of flooding, giving wildlife somewhere to live and forage, and making the building look better or blend into the landscape. Extensive vegetated roofs normally have no more than a foot of soil and only shallow-rooted plants are selected, preferably ones that are adapted for local weather conditions and can manage themselves with minimal need for irrigation and weeding. There are many plants that will do great even with as little as 4 inches of soil.
Are green roofs a modern invention?
Green roofs are sometimes regarded as a modern 21st invention to combat climate change, but the history of green roofs actually goes back to time immemorial. We are definitely not the first generation to realize that green roofs, including planted sod roofs, provide insulation, or that you can use the space on a flat roof to grow food. Even the ziggurats – massive religious buildings built from stone in ancient Mesopotamia – sometimes had green roofs and roof terraces with shrubs and even trees growing on them.
Other notable old-world examples of green roofs are the roof garden created on top of the audience hall in Roman-Byzantine Caesarea, and the elevated terrace gardens of the illustrious Villa of Mysteries in Pompeii. Roughly a thousand years ago, the Persian travel writer Nasir Khusraw (1004-1088 CE) wrote about how tall multi-story buildings in Fustat, Egypt had gardens on their roofs and how water-wheels drawn by oxen brought water up to them.