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Throughout history there have always been green roofs of various types. Until recently, they had been forgotten or had sunk into obscurity, only to be "re-discovered" and further developed.

Roof greening, roof gardens, roof landscapes have been created against various cultural and financial backgrounds, always depending on the surrounding, limiting factors associated with the location. Roof landscapes are not typical green landscapes, but cultivated landscapes characterized by a certain roof shape and type of roof covering.

The BC Period

The origins of roof greening and roof use stretch back into the distant past. Some experts believe that the custom of "planting hanging gardens on arches or roofs" evolved in the Orient. As early as 900 BC there are reports of roof gardens in the Orient. Climatic conditions, building materials, and lifestyles resulted in architectural styles to suit the region, characterized among other things by flat roofs and the use of the areas these offered.

The most famous example of this was created in the 6th century BC. The Assyrian king Nebuchadnezzar had the famous hanging gardens installed for his wife Semiramis over parts of the palace in Babylon. The gardens were considered one of the seven wonders of the ancient world. They stretched over 40 x 50 m, or an area of 2,000 m2. However, it is misleading to speak of "hanging" gardens, because the magnificent installation rested on a column structure and rose up in steps. Trees that provided shade in the days heat, extravagantly blooming bushes, climbing plants, and aromatic spice gardens fascinated the eye and the nose with their colors and perfume. The highest terrace was between 20 and 30 meters high, and the individual terraces were about 3.5 meters deep. Descriptions of their water-tight foundations with layers of asphalt panels, bricks and mortar proves that they must have been roof gardens which required a solid base as well as constant watering and care. An ingenious irrigation system, taking water directly from the Euphrates, preserved the splendor.

Many well-known Byzantine and Indian miniature paintings depict lush roof gardens and patios. They give us a rough idea of how widespread the roof garden concept was.

Under the Oriental influence, the Adonis cult was passed on to the Greek-Roman world and along with it the custom of planting gardens on flat roofs. The Phoenician god Adonis was a symbol for the creation and decay of nature. Each year, his recurring death was celebrated on imaginatively decorated roof areas and balconies.

The roofs of Roman patrician houses were also sometimes lavishly decorated with plants. Possibly as a result of high prices for land, owners of Roman villas put gardens on their roofs instead of on the ground to supplement their indoor living quarters. They planted flowers, bushes, climbing plants and even fruit trees in large pots, transforming roof patios into beautiful gardens.

The Augustus Mausoleum in Rome was world-famous. Round terraces were built on the 44-meter hill above the marble monument with cypresses growing on them. The fact that some roofs also had fishponds on them gives us an idea of how advanced the culture of roof gardens was!

New impulses in the Renaissance

The mild climate of the south with the flat style of building usual there made it possible to use roof surfaces to ideally complement indoor living space. Roof garden culture was not restricted to the wealthy, but was also widespread in peasant or middle-class circles. Hoffman even sees roof gardens as an "important product from the south". Later, they spread to more northern regions as part of modern architecture. Modern architecture, which demanded that roof areas be used, paved the way for todays roof greening.

Following many centuries when roof gardens and roof greening were almost forgotten, the garden culture of ancient Greek and Roman times was revived in the Renaissance alongside the rest of classical culture. Magnificent roof gardens were planted first in Florence, Rome and Venice, but soon also in other major European cities. In the meantime botanical and gardening knowledge had improved. It had become easier to obtain exotic plants from distant locations. Interesting examples of roof gardens were created, including the Villa Careggi (around 1400), the Roman Museum of Cardinal Andrea della Valle and the Palace of Duke Maffei in Verona (both around 1530).

The terraced gardens of the Nuremberg Kaiserburg of Friedrich III as well as the Park of Borromeo at Lago Maggiore were designed to resemble the Hanging Gardens. They too were planted with trees, vines, and beautiful bushes and spice gardens and were greatly admired by contemporaries.

However, the real roots of roof greening in our latitudes are so-called extensive greening with spontaneous vegetation that grows on its own, Icelandic and Scandinavian earth houses with their covering of grass sods and wooden houses with what we today call grass roofs.

For centuries, grass roofs and grass houses have been built in the cold climate zones of Scandinavia, Iceland and Canada and their beneficial effects utilized. But they also perform useful functions in the hot climate zone of Tanzania.

The highly effective heat storage and heat insulation effect can be seen from traditional, grass-covered roofs. This kind of peat sod grass roof makes houses e.g. in Iceland habitable without any additional heating in winter the heat from cooking and warmth emitted from the human body are sufficient. These roofs consist of two to three layers of peat sods. They are placed on a layer of branches and twigs and covered with grass sods. The roofs reach almost down to the ground and have a very small span, because there is little timber in Iceland and only short branches can be used. Within a relatively short time, a stable covering of vegetation is established on the roof which is suited to the extreme climatic conditions and influenced by the surrounding plants. Although the structure is not in itself watertight, the inclination of the roof ensures that rain and melted water from thawing ice run off quickly enough to avoid any leakage into the house. Originally mostly round or oval, these houses were often partly dug into the peat earth in order to keep heat loss to a minimum. The traditional Norwegian and Swedish grass roof with inclinations of between 22 and 34 degrees, are made, starting at the eaves, by laying 20 cm thick grass sods over a multiple layer of birch bark. The birch bark is very resistant to rotting because of its high tannin content, and it is also fixed down with wood tar. Usually, the supporting structure consists of a mixture of rafters and purlins allowing ventilation of the birch bark. Despite high humidity and frequent precipitation this kind of structure achieves a service life of 60 years. While soil and grass roofs have also been installed on residential houses, especially in Scandinavia grass roofs have mainly been used for agricultural buildings. Grass roofs are still built today in Scandinavia. Often corrugated fiber cement panels or several layers of bitumen membrane are used underneath the layer of soil.

A similar technique was used by settlers in the north of the USA and in Canada 100 years ago to build grass sod houses. It is likely that they brought the building method for these houses with them from northern Europe.

The only traditional grass roofs known in Germany are those on cone-shaped charcoal-burners huts. These have been built in Europe in a similar shape and way for centuries as a shelter and temporary housing. Thin tree trunks placed at an angle are covered usually with hay or bark.

The wood-cement roof common at the turn of the century and into the 20s in Berlin, Gottingen, and Halle had its origins in roof building in Silesia. To protect against fire, a layer of pebbles and clay was applied on top of a reinforced roof structure with a layer of tarred felt. The greening happened by chance as a result of airborne seeds and resembles a wild meadow. About 50 of the originally 2,000 of these roofs in Berlin have survived wars and refurbishment to this day and display a varied and stable plant stock.

17th 19th Century

In the 17th and 18th centuries there were few significant developments and examples of roof greening. It was only from the middle of the 19th century onward that architects and house owners gradually became aware of green roofs again. In the Baroque period, the building expert Marperger (1656 1730) recognized the importance of green roof areas and advocated the idea in public.

Some 150 years later, Carl Rabitz of Berlin informed the public about the advantages and disadvantages of various types of roof and expressly recommended flat roofs because of the wide variety of possible uses for them. Simultaneously, he advised using his invention, volcanic cement, as the ideal covering. His roof structures were a little more expensive than felt roofs, but he considered them much cheaper than tile, slate or zinc roofs. He even produced a plaster model of his own villa with roof garden to show at the Paris World Exhibition in 1867, making the idea known to a broader public. Rabitz had a clear understanding of the insulating effect and the favorable influence on the interior climate. He also recommended a suitable substructure, insulation material, humus layer, irrigation options, wind protection, and further equipment.

Writing in his book "Roof Gardens" (1988), Roland Stifter describes an amazing roof garden in Munich. In 1874, King Ludwig II had a greenhouse, over 70 meters in length, built on top of the banqueting hall of his Munich residence. It was filled with a lush tropical landscape of inconceivable variety and imagination. In keeping with Ludwigs taste, access to this Indian magic garden was through a gallery in the Moorish style. Painted landscapes formed the background in front of which birds of paradise, nightingales, humming birds and parrots darted about among palm trees, bamboo, orchids, and other exotic plants. The centerpiece was a pond with water lilies, a waterfall, and an arched bridge. There was a small hill with a princes tent on it and behind that a bizarre rocky landscape. Due to technical problems and the huge cost, this project had to be abandoned after some twenty years.

20th century new departures in architecture

The beginning of the 20th century saw new departures in architecture, which led to great advances for roof greening. Some types of modern architecture integrated green roofs into their basic concept.

In 1903 the Perret brothers built their famous apartment house with patios and roof gardens in Paris, three years after Tony Garnier created the first large town-planning project with terraced open areas for the competition Cite Industrielle. In 1912 the terraced house, stepped on two sides and designed by Henry Sauvage was built. Other architects such as Walter Gropius and Frank Lloyd Wright breathed new life into the idea of roof gardens. In 1914 Wright designed his large restaurant in Chicago, and in the same year the roof garden restaurant conceived by Gropius was built on top of the office building in the Cologne "Werkbund" exhibition.

Exceptional efforts were made by Le Corbusier to promote roof gardens, and he planned a large number of spacious roof patios. Le Corbusier is considered one of the first systematic roof greeners. In his famous five points of new architecture, written in 1923, roof gardens came second. After a brief explanation of structural details, Le Corbusier concludes with the words: "The roof garden becomes the favorite place in the house and additionally for the town it means that the built-up space lost is regained." His so-called domino houses were designed in 1914 as a large series, laying the foundation stone in terms of structure and design for the use of roof areas.

Prior to this time flat roofs were considered unusual and elitist, even a little snobbish. But modern architecture dared to integrate flat roofs into the living space of the building. In line with the social demands of new building, the flat roof and the living patio were discovered as offering new scope. Le Corbusier put it like this: "Is it not against all logic when the upper surface of a whole town remains unused and reserved exclusively for a dialogue between the tiles and the stars?"

Despite the fact that there were some town planners in the first half of this century who recognized the potential and importance of using roof areas, the idea did not take hold. Green roofs had been known in Germany for decades, and projects in Berlin dating from the 20s are still intact today, but still inadequate or mistaken ideas about this kind of green living persisted.

The most impressive examples from this period are:
The Casino Patio in Bern, a large roof greening project, created as a roof garden as early as 1936. Today it boasts 20 chestnut trees with trunk diameters of over 170 cm. A thick layer of nutrient-rich earth even makes it largely unnecessary to fertilize and irrigate the garden.
The roof garden of the former Derry & Toms department store in Kensington High Street, London, also planted at the end of the 30s. It covers approximately 6,000 m2 and consists of a Spanish and an English garden, garden courts in the Tudor style, a water garden and many other smaller elements. The water facilities are supplied from wells, which are up to 120 m deep. Even today this is an impressive, dream-like garden landscape, located, as it is around 35 m above a shopping street in the middle of London.

However, these are isolated examples. It was above all extra building costs and the fear of serious structural damage that worked against the wider application of the roof greening idea. One person who knew about this all too well was Adolf Loos, who faced criticism for his terraced Scheu House, because the technical problems resulting from increasing demands for perfection remained largely unsolved.

The 50s to the 70"s: Cautious advances

In the post-war period individual roof gardens were built in Germany, while in other European countries more and more examples can be found in trade magazines such as the large "Schanze" in Bern (1964) or the "Kantonskapitel" in Basle (1971). Up to the 70s roof greening systems were largely used only on substructures such as underground car parks and subways. However, these were often integrated in new residential areas as green spaces, which people could use. Huge damage to the sealing layers due to roots penetrating made extensive repair work necessary. Special sealing techniques for green roofs were not yet available at this time, and the vegetation problems associated with the types of plant used were also largely ignored.

Up to the beginning of the 80s little use was made of the possibility of roof greening. The following convictions were widespread:
Flat roofs are usually not built to take such large additional loads
The extra roof construction involves additional costs of DM 150-300/m2
The structure required is larger than that for normal roofs
The necessary knowledge about roof structure, suitable plants, and their care is not available.

The 80s and new developments

Despite structural and vegetation-related problems, green roofs gradually became more established in the 80s, although this was affected repeatedly by crises in the building trade. This "movement" was supported by an exhibition initiated by the BDLA at the Deubau trade fair in Essen in 1973, presenting construction aspects of roof gardens, as well as a special show at the National Garden Show in 1977 on the advantages of roof greening.

Manufacturers created a surge of innovation which inspired research and development activities at universities and encouraged developments. New aspects to be examined were the climatic effects of green roofs as well as questions relating to substrate, drainage, and irrigation. Larger flat roofs were also increasingly becoming necessary, especially on commercial buildings, which could hardly be covered with sloping roofs.

Clear demands for roof greening

In the 70s it became obvious that there was a demand for a generally valid description of the building and vegetation aspects according to the state of the art. This was achieved by FLL in 1982 with the publication of its Principles for Roof Greening, which dealt exclusively with intensive greening. In 1984 it was supplemented by a new examination procedure for checking the root resistance of root protection membranes.

An extensive FLL research project provided information about extensive greening on flat and sloping roofs and its importance. The findings were incorporated into the principles for roof greening. This meant that the basic principles for intensive and extensive greening had been established, so they could be turned into guidelines for roof greening and extended as appropriate. The aspects relating to construction were matched to the guidelines for flat roofs.

The FLL guidelines deal mainly with vegetation requirements and aspects of greening roofs, patios, and facades. They document the current state of science and technology, which has developed over the past 20 years, and are hugely significant in influencing the technical requirements as well as town planning and ecological considerations. Applying them conscientiously in practice ensures reliable results and a high degree of safety.

In the 80s ecological building methods were discussed more widely. Energy saving and environmentally friendly construction was also examined with regard to roof greening. There were various excellent roof greening projects, but one special example from the 80s is the marvelously green Hundertwasser apartment house in Vienna (1983). Initially very controversially discussed, it is now famous as a positive example.

Finally, in the 90s increasing emphasis was placed on quality assurance and improving quality. This includes ensuring that planning regulations are observed as well as checking implementation. In 1997 FLL developed an evaluation procedure for roof greening taking into account an intervention/compensation regulation system. This provides a decision and evaluation method for each phase of planning which helps authorities, property owners and architects by giving them recommendations or concrete information. A system of points establishes a clear building, planning and ecological quality standard, which can be the basis for compensatory or replacement measures depending on the function.

It seems that people have finally realized what opportunities are offered by using roof areas. The number of town residents who appreciate the ecological and economic value of green roofs and who want to be close to nature is growing. It is not only the visual improvement of the cityscape, but also the impact of every little piece of green in the urban environment on the human psyche, which is hugely important for the quality of life in towns.


Roof greening has a long tradition, which has continued to develop so that we can benefit from all the useful experience gained in the past. Today there are adequate technical provisions for safe and sustainable green roofs. Applying them can dispel fears and open up opportunities. It is to be hoped that this will make roof greening in our green-starved towns an ever more popular way of replacing lost nature. Protection from nature is increasingly turning into a protection area for nature.