Green roofs and walls can reduce building energy bills and boost ...
urban gardens
74 BUILT ENVIRONMENT GREEN LIVING
75
Berlin is made up of a patchwork of green roofs, with 8 per cent covered with vegetation
LOUISE MURRAY
Green roofs and walls can reduce building energy bills and boost biodiversity while still being aesthetically pleasing – so why aren’t they more widespread in our cities? By Louise Murray GREEN ROOFS are not a new idea. The early Pictish inhabitants of Orkney and Shetland, the Inuit in Canada and Greenland, and the Vikings in Norway all embraced green roof technology in the form of sod houses to keep warm (ish) in winter and cool in summer. In 1920s Berlin, the designers of the Ufafabrik technical building – where films by the likes of Marlene Dietrich were processed and stored – specified a green roof to help cool the building and prevent the extremely flammable film of the day from causing fires. The roof required minimal maintenance right up until 1995 when it began to leak; the waterproof membrane under the roof was simply replaced. Mention green roofs today and the image that springs to mind is that of a token Sedum-covered roof on an eco-building. “In the 1960s and 1970s green roofs grew out of the Green movement in Germany, it was seen as a good thing to be doing for the planet,” Engineering & Technology [[[STRING1]]] www.EandTmagazine.com
says Dusty Gedge of the Green Roof Consultancy who co-wrote ‘Living Roofs and Walls’, a technical report to support London’s 2008 Plan Policy. “Since then, green roofs have taken off in London at least.”
Varieties of green roof
Green roofs come in several shapes and forms. The simplest is an extensive mixed Sedum roof, planted with several species of tough, drought-resistant succulents that store water in their fleshy leaves and are highly attractive to bees. These require only 8cm of rooting substrate for the shallow-rooted plants and minimal maintenance, though cannot be walked upon to any degree. Extensive roofs need no irrigation and are the lightest of all vegetated roofs. Structural engineer Dave Rayment of London-based Morph Structures says: “Extensive green roofs are relatively lightweight – similar to a
traditional flat roof with gravel – and so don’t have a big impact on the structural design of a building.” Over time, grasses, mosses, lichens and other plant seeds will be brought in on the wind and on bird’s feet and the extensive roof will form a mixed dry grassland habitat. “Dry grassland is a relatively rare habitat in the UK, and biodiverse roofs replicate many of the ecological characteristics of this habitat,” says Gedge, ecologist and urban biodiversity advocate. One of the largest of these roofs in Europe, at 32,000m2, was completed at the Rolls-Royce site in Goodwood, West Sussex, UK, in 2003, and designed by architect Sir Nicolas Grimshaw as a semi-sunken building in a former gravel pit. The green roof allows the building to blend into the sensitive natural landscape of the South Downs. Aside from aesthetics, the roof has attracted the attentions of breeding pairs of ground-nesting skylarks who can raise
broods there without interference from predators. “Costs start from £14/m2 for liners, substrate and plants for an extensive roof that will take approximately three years to achieve 100 per cent surface plant cover. If that planting density is needed on day one, say for big opening impact, then costs rise substantially to approximately £35/m2,” says Martin Kuester of Optigruen Berlin, a leading installation company which has offshoots around the world. Intensive green roofs are characterised by deeper soils of up to 100cm in places to accommodate heavier, more diverse plantings with trees or larger perennial plants and shrubs, and are usually designed to allow access to the occupants of the building – more of a rooftop park or garden. They typically have more elaborate horticultural designs and may include water features or allotments for growing food or cultivating bees. They’re usually irrigated
and require constant maintenance. The best examples capture rainfall runoff, reuse grey water from sinks and showers, and incorporate that into the irrigation system. Expert landscape architects pre-grow trees for this environment in shallow containers, so that they develop a flat root ball, in the same substrate as they will be eventually planted in at roof level. Costs for these intensive roofs start at about £50/m2. These heavy green roofs need deeper roof joists and supporting beams, and care must be taken to ensure that the roof can carry the weight of a fully saturated system, or up to a metre or more of snow cover in winter depending on the geographic location. Semi-intensive green roofs are a mixture of shallow-soiled extensive plantings – where budget is limited or the structure dictates lighter cover – and deeper planting media for greater variation where the roof can take greater loads. Maintenance levels are low.
The combined green roof and photovoltaic solar installation was first introduced in Berlin at UfaFabrik, the International Center for Culture and Ecology, in 1995. Marco Schmidt, landscape architect at the Technical University of Berlin explains: “These hybrid roofs claim considerable benefits over ungreened photovoltaic roofs. In addition to all the normal benefits of a green roof, many claim that the cooling effect of the transpiration from the plants has a positive effect on the performance of the solar panels during the summer by lowering the temperature around the panels. As researchers we have not been able to specifically measure this though.” Schmidt is referring to the optimal operating temperatures for solar panels of around 25°C. A combination roof is also easier to install as the green roof itself can anchor the solar panels without requiring costly penetrative solutions, which may > www.EandTmagazine.com [[[STRING1]]] Engineering & Technology
76 BUILT ENVIRONMENT GREEN LIVING
77
74 BUILT ENVIRONMENT GREEN LIVING
75
Berlin is made up of a patchwork of green roofs, with 8 per cent covered with vegetation
LOUISE MURRAY
Green roofs and walls can reduce building energy bills and boost biodiversity while still being aesthetically pleasing – so why aren’t they more widespread in our cities? By Louise Murray GREEN ROOFS are not a new idea. The early Pictish inhabitants of Orkney and Shetland, the Inuit in Canada and Greenland, and the Vikings in Norway all embraced green roof technology in the form of sod houses to keep warm (ish) in winter and cool in summer. In 1920s Berlin, the designers of the Ufafabrik technical building – where films by the likes of Marlene Dietrich were processed and stored – specified a green roof to help cool the building and prevent the extremely flammable film of the day from causing fires. The roof required minimal maintenance right up until 1995 when it began to leak; the waterproof membrane under the roof was simply replaced. Mention green roofs today and the image that springs to mind is that of a token Sedum-covered roof on an eco-building. “In the 1960s and 1970s green roofs grew out of the Green movement in Germany, it was seen as a good thing to be doing for the planet,” Engineering & Technology [[[STRING1]]] www.EandTmagazine.com
says Dusty Gedge of the Green Roof Consultancy who co-wrote ‘Living Roofs and Walls’, a technical report to support London’s 2008 Plan Policy. “Since then, green roofs have taken off in London at least.”
Varieties of green roof
Green roofs come in several shapes and forms. The simplest is an extensive mixed Sedum roof, planted with several species of tough, drought-resistant succulents that store water in their fleshy leaves and are highly attractive to bees. These require only 8cm of rooting substrate for the shallow-rooted plants and minimal maintenance, though cannot be walked upon to any degree. Extensive roofs need no irrigation and are the lightest of all vegetated roofs. Structural engineer Dave Rayment of London-based Morph Structures says: “Extensive green roofs are relatively lightweight – similar to a
traditional flat roof with gravel – and so don’t have a big impact on the structural design of a building.” Over time, grasses, mosses, lichens and other plant seeds will be brought in on the wind and on bird’s feet and the extensive roof will form a mixed dry grassland habitat. “Dry grassland is a relatively rare habitat in the UK, and biodiverse roofs replicate many of the ecological characteristics of this habitat,” says Gedge, ecologist and urban biodiversity advocate. One of the largest of these roofs in Europe, at 32,000m2, was completed at the Rolls-Royce site in Goodwood, West Sussex, UK, in 2003, and designed by architect Sir Nicolas Grimshaw as a semi-sunken building in a former gravel pit. The green roof allows the building to blend into the sensitive natural landscape of the South Downs. Aside from aesthetics, the roof has attracted the attentions of breeding pairs of ground-nesting skylarks who can raise
broods there without interference from predators. “Costs start from £14/m2 for liners, substrate and plants for an extensive roof that will take approximately three years to achieve 100 per cent surface plant cover. If that planting density is needed on day one, say for big opening impact, then costs rise substantially to approximately £35/m2,” says Martin Kuester of Optigruen Berlin, a leading installation company which has offshoots around the world. Intensive green roofs are characterised by deeper soils of up to 100cm in places to accommodate heavier, more diverse plantings with trees or larger perennial plants and shrubs, and are usually designed to allow access to the occupants of the building – more of a rooftop park or garden. They typically have more elaborate horticultural designs and may include water features or allotments for growing food or cultivating bees. They’re usually irrigated
and require constant maintenance. The best examples capture rainfall runoff, reuse grey water from sinks and showers, and incorporate that into the irrigation system. Expert landscape architects pre-grow trees for this environment in shallow containers, so that they develop a flat root ball, in the same substrate as they will be eventually planted in at roof level. Costs for these intensive roofs start at about £50/m2. These heavy green roofs need deeper roof joists and supporting beams, and care must be taken to ensure that the roof can carry the weight of a fully saturated system, or up to a metre or more of snow cover in winter depending on the geographic location. Semi-intensive green roofs are a mixture of shallow-soiled extensive plantings – where budget is limited or the structure dictates lighter cover – and deeper planting media for greater variation where the roof can take greater loads. Maintenance levels are low.
The combined green roof and photovoltaic solar installation was first introduced in Berlin at UfaFabrik, the International Center for Culture and Ecology, in 1995. Marco Schmidt, landscape architect at the Technical University of Berlin explains: “These hybrid roofs claim considerable benefits over ungreened photovoltaic roofs. In addition to all the normal benefits of a green roof, many claim that the cooling effect of the transpiration from the plants has a positive effect on the performance of the solar panels during the summer by lowering the temperature around the panels. As researchers we have not been able to specifically measure this though.” Schmidt is referring to the optimal operating temperatures for solar panels of around 25°C. A combination roof is also easier to install as the green roof itself can anchor the solar panels without requiring costly penetrative solutions, which may > www.EandTmagazine.com [[[STRING1]]] Engineering & Technology
76 BUILT ENVIRONMENT GREEN LIVING
77
