Architect's Knowledge ResourceDocuments
Vegetation in Architecture
By Clare Miflin, RA, LEED AP
The global population is increasing rapidly, and by next year over 50 percent, some 3.3 billion people, will live in urban areas. While cities offer opportunities for living a life with a low ecological footprint, they suffer from pollution, noise and remoteness from nature. Integrating vegetation into the urban fabric allows us to improve 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 (an affiliation between humans and other living organisms) to inhabitants, increase the ecological productivity of the site, and connect buildings with their unique local environment. While the possible benefits are great, design considerations and responsibilities are atypical. A multidisciplinary design team will need to think holistically, commit to strategies and collaborate in order to successfully incorporate vegetation into green buildings.
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 also, 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 to70 percent.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 summertime cooling strategies. It can also be part of the stormwater management and waste water treatment systems. Vegetated roofs and facades 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 inch substrate) have been shown to retain 70 to 100 percent of summer rainfall and 40 to 50 percent 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 acquifers instead of entering a piped sewer system.
More extensive purification of grey and black water can be done by biological wastewater treatment systems that use aquatic and wetland plants in conjunction with bacteria, algae, and other organisms. (Grey water is wastewater from bathing, hand-washing, dishwashing and laundry; black water contains sewage.) A constructed wetland is an exterior system, and serves as an intermediate step between a septic tank and a drainfield, making pollution of groundwater less likely. An interior system treats grey and blackwater waste within planted tanks in a greenhouse space and may reuse the water for nonpotable uses.
Indoor plants purify, humidify and oxygenate air, improving indoor air quality greatly. Research at the University of Guelph in Ontario 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.
Figure 1. University of Guelph 4 story biofiltration plant wall. (Photo: Ken Kerr)
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 up 2 to 4°F if just 6 percent of the cities rooftops were greened.5 Plants, especially locally 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.
Human food production within buildings or on rooftop greenhouses is also a possibility. The ecological cost of transporting food thousands of miles from farm to table is huge, and indoor urban agriculture allows food production year round for local consumption. Studies have been done to incorporate hydroponic production of crops with a double skin curtain wall - integrating the benefits of cooling, shading and fresh air into the building’s HVAC systems (Figure 1).
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”. Studies have been done similar to those showing the benefits of daylighting to student learning in schools, retail sales or employee productivity. Views of plants have been shown to increase worker productivity, decrease absenteeism and reduce recovery times for patients in healthcare settings. 6 Plants are part of the high quality environment that sustainable architecture should provide. As building technology improved throughout the 20th century the possibility of providing a uniform environment led to many buildings losing their vital connection with their environment. People are now beginning to question the desirability of that uniformity. Many opportunities for richness and meaning come from connecting a building to its environment, animating architecture through the play of daylight on a wall, the passing of a breeze, or the variety of light, shade and color that plants can give.
Figure 2. Light and shade through a grape vine screen. (Photo: Clare Miflin)
Opportunities for integrating vegetation within architecture:
• Green roofs
o Options include thin ‘extensive’ green roofs (2 to 6 inches), thicker ‘intensive’ green roofs (typically an accessible roof garden) or removable modular green roofs.
o Green roof plants are typically sedums and other rocky alpine plants as they can tolerate the extreme conditions and are virtually maintenance free. You may choose to use other plants for aesthetics or for increased biodiversity and to provide habitat for a larger variety of animals. Although many green roof systems incorporate a rainwater detention layer – in the form of an eggcrate like matrix – other plant mixes on extensive roofs will often need supplemental irrigation. Wetland green roofs are being designed that purify wastewater, create a diverse wetland ecology, and keep the roof much cooler throughout the summer than a dry green roof. 7
o Green roof systems typically use special lightweight growing mediums, rather than soil, that can be tailored to the chosen plant mix. The structural engineer will need to consider the additional weight of the green roof.
o Architects have integrated vine covered overhangs at the edge of a green roof to shade glass facades, and have terraced roofs allowing a building to become part of the topography of a park (Figures 3 and 4).
Figure 3. Ricola Marketing Building, Switzerland,by Herzog and Demeuron Architects. (Photo: Clare Miflin)
Figure 4. Acros Building, Fukuoka, Japan by Emilio Ambasz Architects. (Photo: DK Preston)
• Green facades
o Facades 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.
o Climbers may be self-clinging or they many 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. Some climbers with aerial rootlets, such as English Ivy (Hedera helix) may damage brickwork as the roots penetrate the mortar joints.
o Designers need to know a climber’s growth speed, maximum height, and whether they like to grow towards the light or can be trained horizontally. They will also need to consider the visual characteristics in all seasons.
o Vines typically like well-hydrated fertile soil and the space for this will have to be coordinated with the foundation design.
o Plants are exposed to more extreme conditions on buildings, especially at higher stories. Suitable hardy species will need to be chosen.
o Vines attract wildlife – wanted or unwanted. While butterflies and hummingbirds are always welcome, some birds can be noisy, and some green facades have attracted snakes or other pests. This issue should be discussed with the landscape architect and possibly a local ecologist.
Figure 5. (Finnish Embassy, Washington by Heikkinen-Komonen Architects. Photo: John Hill)
Figure 6. Musee du Quai Branley by Jean Nouvel Architects, vegetated wall by Patrick Blanc. (Photo: Rolando G from Flickr)
Exterior green walls
o Walls can be planted with mosses, or plants in pockets of the walls to form a green wall.
o Retaining walls can also be made up of modules that have space for planting.
o Designed green wall systems may have soil held in compartments, or be hydroponic – where bare roots are kept moist and irrigated with a nutrient solution.
• Interior green walls
o Interior walls can be vine covered. Walls can be covered in panels which hold soil in chambers, allowing water to drip down through them, and plants to be grown within them. Alternative systems put plants in pockets in a felt curtain, and irrigated through hydroponics.
o Planted walls can be designed to purify air passing through the wall.
• Interior or exterior planting beds
o Built-in planting beds can be designed as architectural elements. Courtyards and atria can be intensively landscaped.
Figure 7. Plantwall at Uppsala Konsert & Kongress, Sweden. (Photo: Green Fortune)
Figure 8. Interior courtyard of Alterra, The Netherlands. (Photo: Behnisch Architekten)
Successful integration of plants into buildings and their systems requires a team approach. Maintenance requirements need to be considered from the outset. The client, landscape architect, architect, structural engineers, civil engineers, mechanical, electrical, and plumbing engineers and an ecologist may all need to be involved. Most of these team members are not used to designing with regard to time. 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 very easy to think of vegetation as another building material that can be used in any orientation, exposure or size. Plant textures applied to renderings can seduce the architects and clients into thinking that this is possible, and the real world installation may well fall short of expectations. However, 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.
An ecological approach calls for the use of native plants in exterior locations. (Indoor plants will normally be tropical or other warm weather plants, since the indoor environment is always warm.) Native plants offer many advantages, link to the region, and greatly increase the available habitat for animals. Adapted, or non-invasive plants may also be considered, but it is worth considering the level of ecological productivity and animal life supported by native plants can be orders of magnitude higher.
A holistic sustainable approach to design offers many synergies. Using plants to treat wastewater increases their growth and possibilities of summer time cooling. At the same time it increases biodiversity and habitat. Studies have looked at combining photovoltaic (PV)and green roofs and found that there may be benefits to both – the PVs are more efficient since they are kept cooler and the green roofs benefit from some shade.8 However, there will be situations where tradeoffs need to be made. When buildings are aiming to be zero energy and zero waste the whole building skin becomes a precious opportunity to harvest environmental benefits, such as whether a surface should be clad in solar panels, vegetation or glazed. The design team needs to think of the whole picture, and measure advantages and priorities, while avoiding token gestures of greenness.
Clare Miflin, RA, LEED AP is an associate with Kiss + Cathcart, Architects of Brooklyn, NY. She is working on several architectural projects that integrate vegetation with sustainable strategies.
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.
www.greenroofs.net (Green Roofs for Healthy Cities) 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.
www.greenroofs.com is a website set up by a landscape designer and green roof enthusiast. Has a lot of information and links.
“Planting Green Roofs and Living Walls” by Nigel Dunnett, Noël Kingsbury, 2004 Timber Press.
“Green Roofs: Ecological Design And Construction” by Earth Pledge Foundation, published 2004 Schiffer Publishing.
1. Paul Mankiewicz, Gaia Institute, Bronx NY, personal communication.
2. p. 131 ‘Planting Green Roofs and Living Walls’ by Nigel Dunnett, Noël Kingsbury, referring to research done by Steven Peck et al from the Green Roofs for Healthy Cities group in Chicago.
3. p. 49 of ‘Planting Green Roofs and Living Walls’ by Nigel Dunnett, Noël Kingsbury, referring to research done by Steven Peck et al from the Green Roofs for Healthy Cities group in Chicago.
5. Greenroof infrastructure monitor.
6. In 1984, Roger Ulrich, PhD, of Texas A&M University, 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, England 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 in Oslo, Norway.
7. Green roof infrastructure monitor, Fall 2007 ‘Just Add Water: Wetland Green Roofs for Enhanced Performance’ by Christine Thuring, MSC and Rana Creek Staff.
8. Green roof infrastructure monitor, Spring 2007 ‘Positive Interaction Between PV-Systems And Extensive Green roofs’ by Manfred Kohler, Werner Wiartalla and Rene Feige.
Keywords: Building Performance, Sustainable, Sustainable design knowledge, Building envelope, Plant material, Vegetation, Green roofs, Green facades, Article