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Vertical green

May 1st, 2009 / By: / Continuing Education

The global population is increasing rapidly, and by 2010 more than 50%, some 3.3 billion people, will live in urban areas. While cities offer opportunities for living with a low ecological footprint, they suffer from pollution, noise and remoteness from nature. Integrating vegetation into the urban fabric improves these quality of life issues while offering many innovative opportunities for “green” architecture. Whether part of a highly engineered wetland or simply a low-tech way of providing dappled shade, plants can be part of a sustainable design solution. At the same time, they offer biophilic benefits to inhabitants, increase the ecological productivity of the site and connect buildings with their unique local environment.

Textiles can play an important role in integrating plants into the urban environment, whether through transport of water and nutrients, protection of the building envelope from moisture, holding plant material together or supporting vine growth.

Sustainable advantages come through integration of vegetation into the building envelope and into its mechanical and plumbing systems. Basic architectural strategies can include using evergreen vegetation as a buffer against prevailing cold winter winds. Evergreen vines on a wall trap an insulating cushion of air and reduce wind chill. Deciduous vegetation can be used for seasonal shading and through evapotranspiration, can cool the surrounding air. Depending on climate, well irrigated vines (preferably with grey or rainwater) can result in temperatures up to 10°F cooler than the surrounding air.1 It has been calculated that a 10°F (5.5°C) reduction in the temperature immediately outside of a building can reduce the amount of energy needed for air-conditioning by 50 to 70%.2

Many sustainable architects have the benefits of xerioscaping (landscape that does not require supplemental irrigation) foremost in their minds. Although it is important to eliminate the use of potable water for plant irrigation, the design team should consider sources of wastewater that can be used. Irrigation can greatly increase the rate of growth of plants, their rate of evapotranspiration and their possible contribution to summer cooling strategies. It can also be part of the stormwater management and waste water treatment systems. Vegetated roofs and façades and designed landscapes can allow downsizing or elimination of conventional plumbed stormwater systems. Especially important in areas with combined storm and sanitary sewers, this helps reduce overloading of the system with resultant overflows of raw sewage into nearby waters. Extensive green roofs (with 4 in. substrate) have been shown to retain 70 to 100 % of summer rainfall and 40 to 50% of winter rainfall.3 Designed landscapes such as bioswales, rain gardens and constructed wetlands purify stormwater and allow it to infiltrate into the ground to recharge the aquifers instead of entering a piped sewer system.

Indoor plants purify, humidify and oxygenate air, improving indoor air quality greatly. Research at the University of Guelph, located in Guelph, Ontario, Canada, led to a design for an indoor green “biowall” which circulates air through it, oxygenating the air and removing pollutants, especially volatile organic compounds and carbon monoxide.4 Purifying air in this way can lead to lower requirements for exterior air and associated conditioning, lessening energy demand for the building’s HVAC system.

When cities increase the amount of vegetation within them, reduction of particulates, pollution and carbon dioxide, and lessening of the urban heat island effect can be observed. A 2002 study in Toronto found that urban summertime temperatures in the city could be reduced by 2 to 4°F if just 6% of the cities rooftops were greened.5 Plants, especially native ones, also provide food and habitat for birds and insects, enhance biodiversity and the site can be made ecologically productive, sequestering carbon dioxide for the life of the plants (and beyond as carbon within the soil).

Perhaps the most cost-effective and rewarding benefit of integrating vegetation into buildings is the biophilic connection it gives to building occupants. Biophilia has been defined as “the connections that human beings subconsciously seek with the rest of life.” Views of plants have been shown to increase worker productivity, decrease absenteeism and reduce recovery times for patients in healthcare settings. 6

The following is a selected list of systems that integrate vegetation within a building, highlighting the possible uses of textiles within the construction.

Green roofs

Green roofs include thin “extensive” green roofs (2 – 6 in.), thicker “intensive” green roofs (typically an accessible roof garden) or removable modular green roofs.

Extensive green roof plants are typically sedums and other rocky alpine plants because they can tolerate extreme conditions and are virtually maintenance free. Intensive green roofs can support a larger variety of plant species. Although many green roof systems incorporate a rainwater detention layer — in the form of an eggcrate-like matrix — many green roofs will need supplemental irrigation, which can be provided by greywater or stored rainwater. This can be dispersed by a drip irrigation system or by a layer of felt below the surface and irrigated from one edge. A well irrigated green roof can keep the roof much cooler throughout the summer than a dry green roof.7

Drainage mats are used on green roofs to draw stormwater away, avoiding waterlogging of plants and growing medium. A geotextile above the drainage mat will exclude soil and silt. Geotextiles are also used for turf reinforcement and to hold together pre-vegetated planting mats.

Green façades

Façades can be vine covered. Trellises can keep vines largely within designed areas and can be placed in front of glazed areas, allowing deciduous vines to provide seasonal shading of the interior spaces. Climbers may be self-clinging or may need supports. Certain climbers require certain types of supports — some twine around trellises or vertical or horizontal supports while others have suckers or aerial roots to attach to walls. Steel cable or strong plastic meshes can be used as the support for vines. The Ricola Marketing Building in Basel, Switzerland, by Herzog and deMueron Architects has a large overhang with a textile mesh supported between cantilevered plastic tubes that supports trailing vines.

Green walls

Walls can be planted with mosses or plants can be placed in pockets of the wall to form a green wall. Retaining walls can also be made up of modules that have space for planting.

Designed green wall systems may have soil held in compartments, but the most successful ones are often hydroponic: bare roots are kept moist and irrigated with a nutrient solution. Patrick Blanc, probably the world’s most experienced green wall designer, put plants in pockets in a felt curtain, and irrigates through hydroponics. The felt holds a substantial amount of water, which allows the roots to remain constantly moist.

Successful integration of plants into buildings and their systems requires a team approach. Maintenance requirements need to be considered from the outset. When integrating vegetation into buildings architects need to be aware how their design will look in each season and before and after the optimal growth period. It is easy to think of vegetation as another building material that can be used in any orientation, exposure or size. Irrigation is probably the most critical issue, and will need to be monitored and maintained throughout the life of the building. Many built examples show that where a team member has close knowledge of plants and their requirements, and the whole team works together to make the installation a reality, then incredibly lush, verdant installations can be created.

Clare Miflin, RA, LEED AP, is an associate with Kiss + Cathcart, Architects, with 14 years of experience. She is working on several architectural projects that integrate vegetation into their sustainable strategies.

Resources

A landscape designer and green roof enthusiast has a Web site at www.greenroofs.com with a lot of information and links.

Environmental Building News magazine, available online as part of the Building Green Suite of tools at www.buildinggreen.com has good articles on all sustainable building issues.

Green Roofs: Ecological Design and Construction by Earth Pledge Foundation (Atglen. Pa.: Schiffer Publishing, 2004)

Green Roofs for Healthy Cities (www.greenroofs.net) produces the Green Roofs Infrastructure Monitor which includes articles and the latest research on green roofs and facades. It also offers courses in green roofs and green walls.

Planting Green Roofs and Living Walls by Nigel Dunnett and No”l Kingsbury, (Portland, Ore.: Timber Press, 2008)

Notes

1. Paul Mancowicz, Gaia Institute, Bronx N.Y., personal communication.

2. Nigel Dunnett and No”l Kingsbury, Planting Green Roofs and Living Walls (Portland, Ore.: Timber Press, 2008), p.131, referring to research done by Steven Peck et al from the Green Roofs for Healthy Cities group in Chicago.

3. Nigel Dunnett and No”l Kingsbury, Planting Green Roofs and Living Walls (Portland, Ore.: Timber Press, 2008), p.49, referring to research done by Steven Peck et al from the Green Roofs for Healthy Cities group in Chicago.

4. Andrew Vowles, “Guelph-Humber Plant Wall a Breath of Fresh Air, www.uoguelph.ca/atguelph/04-11-10/featuresair.shtml

5. Green Roof Infrastructure Monitor.

6. In 1984, Roger Ulrich, Ph.D., of Texas A&M University College Station, Texas, showed that patients whose rooms overlooked vegetation recovered faster after gallbladder surgery and required less pain medication than patients without a view of nature. A study by Professor Derek Clements-Croome at the University of Reading, Berkshire, United Kingdom, compared the performance of schoolchildren in classrooms with and without plants. Better results were achieved in classrooms with vegetation, the study said. Absenteeism relating to “Sick Building Syndrome” also decreased when plants were part of the office, according to research by Professor Tove Fjeld of the Agricultural University of Norway, in Oslo.

7. Christine Thuring, MSc and Rana Creek Staff, “Just Add Water: Wetland Green Roofs for Enhanced Performance,” Green Roof Infrastructure Monitor, Fall 2007.

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