THE ROLE OF GREEN ROOFS IN COST-EFFECTIVE CITY GREENING
Rune Kongshaug, Vikram Bhatt
1McGill University, School of Architecture, Minimum Cost Housing Group (MCHG)
The role of green roofs is here considered within the framework of how to optimize land-use as a response to rapid urbanization in both Northern and Southern cities. Comparing high-cost, green roofs with alternative low-cost greening solutions—both at and above grade—the authors
suggest how green roofs could benefit from a minimum cost perspective, which seeks to maximize city greening and target ordinary residents in the most cost-effective manner, employing participatory, community-based design methods. Community gardens, rooftop container gardens, and urban agriculture illustrate how green roofs could be low-cost, participatory, and community-based and act as engines for urban renewal, strengthening social networks and residents’ self-reliance, promoting equitable access to land and economic growth.
Our paper is a critical review of the benefits of green roofs as compared to other ecological and community-friendly uses of under-utilized urban spaces. The topic of green roof design and implementation needs to be understood in a wider framework how to best prioritize resources for the greening of cities. To what end and for whom do we practice urban planning and design? In this paper we equate urban design and architecture as a means to provide design solutions for people. Unfortunately, the general design practice of planners, urban developers and architects has primarily looked at and served wealthy clients and produced expensive solutions for which demand and application is limited. The challenge is to produce rooftop garden solutions that ordinary people can afford. Participatory, community-oriented and low-cost
approaches to city greening are in great demand and are required because they contribute to efficient land-use, and help redress the balance between urban spaces for living (shelter) and spaces for growing (ornamental gardens and urban agriculture), which is an essential component of raising the quality of living in most urban sites. This view has been expressed by
1 Acknowledgements: For the Edible Landscapes seminar on Montreal community gardens (2002) and
publication (2004), a special recognition goes to all participants of the research seminar: Ms. Yingwei Cui, Ms. Yingzhou Du, Mr. Qiang Fu, Ms. Xiao Tong He, Mr. Rune Kongshaug, Mr. Sachin Narkar, and Ms Li Xiao. For assistance on research of Montreal green roof projects, a special thanks to Mr. Elikem Ayitey, MUP.
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national governments? requests written down in the Harare Declaration (1). The sponsoring by granting agencies such as the UN-HABITAT and the IDRC of community-based, participatory projects seeking to leverage phenomena such as urban agriculture as a means for building or
2upgrade worldwide city-sites, further validates this point. The authors use examples of city
greening—which includes hands-on experience of building rooftop gardens, student fieldwork on government-sponsored community gardening—to propose a minimum cost perspective on
the role of green roofs in city greening.
Community-based design for greening and building of sustainable cities
The role of green roofs are considered alongside other greening solutions at grade, within the minimum cost perspective of how to optimize land utilization as a response to rapid urbanization in both the Northern and Southern hemispheres. To this end, we compare problems and benefits associated with retrofit and new green roof projects, with rooftop container gardening, community gardening at grade, as well as urban renewal and housing projects seeking to integrate urban agriculture. We look at how each solution contributes to overall city-greening,
according to: (a) ability to create value for the building’s owner or its residents; (b) ability to involve the community through the design, planning and building stages, training and community outreach; (c) permanent community impacts in terms of increased health and socio-economic benefits, such as job creation, overall social interaction and food security; and (d) monetary cost.
Greening Solutions Urban Upgrading New urban development
Retrofit: Green roofs and Rooftops New green roofs Container rooftop gardening
Vacant lots, parking, streets City and housing design At grade Community gardening Urban Agriculture (UA)
3Table 1: Comparing greening solutions according to urban upgrading or new developments
2 The Minimum Cost Housing Group has just recently received funding from the International Research and Development Center in Ottawa, to conduct a three-year research and design to upgrade and/or build three urban sites incorporating Urban Agriculture: One site will be in each of Africa, Asia and South America. 3 See the Appendix for a table summarizing challenges and benefits of greening solution at and above grade.
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The minimum cost design perspective
The minimum-cost approach to architecture, and in particular housing design, is concerned with serving the largest possible number of residents, which (often) means to service the urban poor. The poor urban resident is not the typical architectural client, and is often left out of the city planning and design processes. However, since money is scarce, the minimum cost perspective seeks, first and foremost, to identify design and greening solutions that minimizes cost, yet seeks to maximize community participation and social outcomes. The residents are themselves the main asset in this participatory design exercise, and as design professionals, we seek to leverage their self-reliance and ―entrepreneurial spirit‖ and their ability to organize a community-based response to improve their situation. This approach also relies on innovative funding strategies such as micro lending to individual residents, as part of community-wide efforts to create jobs, building new or upgrading existing housing. Most recently, as part of an a world-wide effort to upgrade or build three urban sites incorporating urban agriculture, the minimum cost approach seeks to leverage municipal land and existing infrastructure and other ―in-kind‖ contributions that poorer city partners can commit, thus diminishing the reliance on hard cash. Finally, the minimum cost perspective adopts an attitude of learning from those
poorer residents who, through their informal housing, urban agriculture and gardening inform us about residents’ true needs and how they organize ―bottom-up‖ through grassroots movements
and social activism. Finally, this approach seeks to define new solutions and inform design professionals, planners and policy-makers how to green and upgrade existing or build new, more efficient and equitable cities.
In this perspective, green roofs generally present a maximum-cost and complex endeavor that may fit large and luxury-end construction. How to channel the current green roof movement to develop a credible scenario for large-scale greening of cities at minimum cost? In this respect, we found new commercial green roofs of limited value compared to innovative ways that exploited underused spaces both at grade and retrofit roofing projects, providing a potential niche market for green roofs, and a potential new direction for the green roof movement that would warrant lower-cost, retrofit and do-it-yourself solutions, and that would incorporate community-based design methods.
Lessons from North and South: city-greening as an engine for urban renewal
Urban growth is inherently accompanied with land-use pressures, which prevent efficient or equitable land utilization. For example: In Southern cities, the appearance of a large informal
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housing sector (squatter settlements or slums) has traditionally been met with the official response of displacement of residents to outside the city core, bulldozing of their settlements, with interdiction of urban agriculture—horticultural practices or raising of livestock in the city—
deemed contrary to sound city planning principles or to represent a health hazard. Land prices
4are usually higher near the denser city center, and it is generally assumed that Laissez Faire—
speculative market forces, municipal authorities and real estate developers—would assure the
most efficient land- and resource-use. In Northern cities, planning new urban development has since WWII deliberately relied on high levels of individual car ownership, high energy consumption and low energy costs, accentuating a trend towards a diffusion of the city core—
traditionally diverse in terms of both cultural and socio-economic diversity, commercial and residential mixed uses—into more monotonous spatial divisions made up of garden suburbs for living, urban centers paved with asphalt for parking, working or shopping (where trees are usually described as ―amenities‖), and tree-less ―rural‖ areas for agro-industry.
Neither in the North or South, does current city planning practice seek to provide equitable access to land resources, or to leverage greening efforts in such a way as to act as engines for urban renewal that promotes social inclusion, nor does conventional architecture and urban design practice have a stated goal to diminish the current gap between the richest and the poorest or society, which could serve as a roadmap for the design practice. This problem may be even more pressing in the Southern cities, which are surpassing the more developed North, both in terms of the overall size of cities and urban growth rates, yet adopting city building patterns of the North, such as the suburban single-detached bungalow as a ―way of life‖
UN-HABITAT estimates that close to half of the world’s population, is now living in cities and this
number will grow to 60 percent by the year 2015 (2). Conventionally, cities have functioned as centers of commerce and manufacturing, and of course, they do continue to serve as seats of power and culture. Also, informal, not officially planned, urban phenomena such as urban agriculture (UA) are increasingly recognized as engines for urban renewal, poverty alleviation, social empowerment, and healthy living in cities. UA includes horticultural practices and raising livestock inside the cite for pleasure, commerce or food security, which have traditionally been
4 Here alluding to the liberal economical theories Adam Smith, whereby market forces will assure the greater social good, from which also derives the expression “greed is good.”
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considered a strictly rural activity, now observed as a spreading urban and peri-urban
phenomena in Northern and Southern cities alike (3).
Lessons from greening at grade
For rooftop gardening to present a broad-based design ―solution‖ to urban problems, we
propose a practical framework to compare and contrast alternative greening solutions, in which the benefits of greening rooftops can also be appreciated. This presentation contrasts newly developed, ―fancy‖ and expensive garden roof projects with more ―laid-back‖ minimum-cost yet
highly aesthetic interventions, suggesting that do-it-yourself and community-driven retrofit projects can produce desired social interactions and positive neighborhood impacts.
This study is based on the authors’ own experiences in the design and construction of two roof
gardens: one a container garden built by a research team, the other a green roof built for residential tenants, as well as field research conducted by the authors, as published in Rooftop Wastelands (4) and Edible Landscapes (5). The objective of our work is to optimize uses of
under-utilized land and hence redress, qualitatively and quantitatively, the balance between built live-work spaces and open spaces dedicated for growing both for pleasure and sustenance. We will use the following greening and rooftop garden solutions as illustrations:
At grade New roof Re-fit
High Cost Nun’s Island condos, Place Bonaventure, Luxury dwelling, New
Montreal (2003) Montreal (1967-1997) York (2002-03)
Low Cost City of Montreal University Settlement
Community Gardens Community Center,
(1974-current) Montreal (1974-76)
Table 2: Sample Greening and Rooftop Gardens Serving as Illustrations.
Similarly to the evolution of community gardening and urban agriculture, green roofs could also benefit from a community-based, minimum cost approach. In particular, a community-based rooftop greening project should bring together several stake-holders and community groups: city officials, individual owners, community representatives, and seek to: involve residents and community members during the planning and design stages, compensate individual owners for expensive up-front costs and community-benefits generated in terms water retention, air quality
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improvement, visual impact, and—why not?—encourage owners to engage with the community
through outreach programs permitting controlled community access and/or training.
Public and private ownership, and grassroots activism
Gardens in cities exist in surprising forms, ranging from potted plants in windowsills, private gardens, community gardens, vacant and parking lots, container gardens on roofs and balconies, and green roofs. Different forms of gardening present distinct challenges: land tenure, security, structural requirement, access, planning, design and ongoing maintenance, and, of course, the cost. The opportunities are also distinct: community impact, privacy, income-potential and environmental payback. One solution does not fit all.
Private ownership, an individual owner or a condominium seeking public or non-profit partnerships, should thus be encouraged in terms of: (a) facility in obtaining permits, city approvals and insurance, (b) financing in terms of matching public grants and tax credits, and in-kind financial support, e.g. building material, horticultural supplies and technical expertise.
Public ownership in the form of community centers, schools, etc., or social housing (non-profit cooperative housing) may be set up similarly to community gardens in that it can: (a) provide initial public funding for retro-fit green roofing projects, structural improvements and materials for qualifying community organization that can demonstrate organizational commitment, (b)
leverage existing public infrastructure, such as staff and resources dedicated to serve municipal public parks for ongoing maintenance, (c) reduce overall cost and maintenance by encouraging a selective, membership-driven process available to the community at a small yearly membership fee and subject to rules and regulations.
To this end, the City of Montreal, which facilitates community gardens and urban agriculture by leveraging existing public infrastructure, is a case in point to be contrasted with most cities. Most cities (consciously or unknowingly) discourage the use of under-utilized vacant lots or roofs for gardening and urban agriculture practices. As an owner-builder in both New York City and Montreal, I have experienced first-hand the lack of incentives for owners wanting to build a green roof in New York. Another example: while community gardening in Montreal and New York have achieved similar levels of popularity—76 city-sponsored gardens on the island of
Montreal for 1.8M residents (6), and 189 smaller gardens on the island of Manhattan serving 1.5M residents—the levels of city support and social activism varies greatly. New York gardens
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survive only due to grassroots activism of organizations such as ―Green Guerillas‖ who battle
city authorities and their policy of either selling off land or bulldozing community gardens (7).
A participatory and community-based approach to the development of green roofs may need to identify, then align itself with and leverage, existing social movements and grassroots activism of community gardening in order to reach a large numbers of residents, and achieve a city-wide greening of roofs.
Design methods and tools
A key design objective for green roofs is that it ought to be a cost-effective greening solution, thus affordable to the community at large. Design processes that engages the owners, residents or the community at large, stand to facilitate the development of low-cost design solutions, if anything because it focuses design goals around common needs and objectives,
5instead of around individual wants, and thus helping to prioritize scarce resources. Here the
design practitioner acts as much as a ―facilitator‖ as the architect in the classical sense, in
generating a community response. It is the methods of observation and ability to create a multi-stakeholder process, which can inform the various participants—rather than the final blueprint—
that becomes the main deliverable of the minimum cost, community-based design method.
Reducing the scale of observation to human dimensions
A dweller-grower is here coined to designate an urban resident who is also a gardener. The garden may not be attached to the gardener’s house, but when considering the relationships
between living and growing spaces in the city, matters of distance and scale become important, first in terms of shared urban spaces and the social interactions they crate, but also in terms of creating a balance between built, human structures, and growing organic, natural forms. An example from observing informal building and growing practices for people by people in poor settlements in India, first alerts us to the ―riches‖ inherent in traditional settlements; However monetarily poor, observing informal settlements (so-called slums) teaches us important lessons of human scale. For example, working, cooking and eating activities would take place on the floor rather than in a seated position, and surprisingly small indoor and outdoor spaces give rise to different activities, such as bicycle repair, weaving, cooking. In this setting, a tree does not have ornamental value only, but provides shade, fuel and food with a minimal up-front
5 Gandhi shall have said something like: There is enough for everyone’s needs but not for everyone’s wants.
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investment. The simple lessons of trees, and its various productive uses, are seldom transferred from the informal settlements to formal city planning and design practice, however: Trees on the architectural plan are usually for ornamental value, only, not providing detail on growing cycles, different species or varieties suited for local climate, or local customs (8).
Sharing growing secrets in community garden spaces
From the architect’s perspective, one of the most challenging elements of considering the merits of low-cost gardening solutions, is to view lettuce and chard on equal footing with brick and mortar. After all, a garden’s value needs to be considered against other alternatives such as parking, housing, commercial development, roads and parks for recreational use. The length of the growing season, size of containers, methods of irrigation and fertilization, ease of physical access, as well as considerations inter-cropping in tight areas will dictate the choice of plants. In the example of Montreal’s short growing season and community gardens, simple planning
and design tools help transform a small lot—the size of a parking space (9’ x 18’) —into an
effective food garden producing several harvests for an annual investment of less than CAD $47 (9). Some communities had perfected using supports to grow vertically and inter-cropping to the point of having 3-4 harvests in the short Montreal planting season. Cultural differences also exist and give rise to meaningful social exchanges in these tight, community garden: In Montreal, depending on whether the grower-dweller was of Anglo-, French, Indian or South-East Asian origin, the skill-levels and methods applied by gardeners varied widely. Sharing growing ―secrets‖ is part of Community Garden social life, hence the value of community urban gardening as it reinforces the need for and value of shared urban space, social interaction and learning (10). The University Settlement community rooftop container garden, extended the growth season even further, employing re-cycled materials and cold-frame technology with a similarly small investment, and formalized community outreach and training offering gardening classes and thus leveraging further the inter-disciplinary links between the university and the surrounding community (11).
Building topography and population density, revisited
Urban land is scarce in some places, but even the most densely populated urban fabrics can accommodate greening at grade, in vacant lots, between railroad tracks, etc. And rooftop gardening has been found to be an attractive solution in lesser dense areas, and ought to be considered as cost-effective even in low-density residential suburbs for community facilities, and for commercial strips on traditionally large mall or warehouse ―boxes‖ that may be greened more
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extensively than surrounding parking lots, and provide important aesthetic and environmental benefits. Also, very densely populated areas do not automatically mean that greening rooftops provides the best and most efficient greening solution, where it may be more pressing to address community-driven projects, with equitable access, at grade. Again, the choice to promote any greening solution over another needs to be based on overall community involvement, social benefits, and whether or not it presents a cost-effective approach to city-greening. Considering the building stock in Montreal, one finds ample room for private and community gardening, at grade, before rooftop gardening becomes a necessity. Yet, the several rooftop community gardens have been developed, including on top of the YMCA in Cote-des Neige (12), demonstrating the underlying community motivations behind urban greening, regardless of topography and density: Where there is a community, there is room for cost-effective greening, even green roofs.
Community Garden Neighborhood Open Built Housing Type Density
Le Mannais Rosemont / Petite 56% 44% Attached Medium
Pere Marquette Prairie (Duplex, Triplex)
Victoria Cote-des-Neiges 80% 20% Detached Low
Bon Voisin Sud-Ouest 66% 34% Semi-detached Medium
Table 3: Topography and Housing Types surrounding Community Gardens in Montreal.
Importance of middle-to-high density urban residential housing
Residential urban and suburban housing is in crisis if one looks at the time spent and distances traveled commuting, and the disappearance of open land to cities: Between 1982 and 1997, the total urbanized land in the United States rose by 47%, from 51 to 78 million acres, while the U.S. population rose by (only) 17% (13). In the minimum cost perspective, the cost of adding peri-urban space for growing would be far less expensive than the cost of developing it for housing. Moreover, the tradition of having a small growing plot on the outskirts of the city is very old and was extensively used in the wartime Europe, but it still exists. It is also important to note that marginal lands can be used for such a purpose, noting that working such lands would not require daily commuting. Examples of peri-urban agriculture, includes in New York the green markets supporting local farmers. In Montreal: organic food coops where people control the food they eat but need not grow it themselves, or ―peri-urban partnerships‖ between residents
and farmers whereby urban residents volunteer for farm work against a share in the harvest, thus helping the farmer keep expenses low (14). Again, between the extremes of the single-detached suburban house and the city high-rise, the minimum-cost approach considers working
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with medium density housing, and seeks to implement low cost retrofit solutions rather than demolition and new construction. As a response to demographic pressures on existing urban housing stock, and the need for urban upgrading and renewal, one can demonstrate that even in badly designed housing one can grow in very small pockets of land, making sure that such growing processes or activities need not be capital-intensive as the rooftop initiatives are.
Residential housing thus constitutes both a potentially important market for rooftop gardening in terms of already existing roofs. In this respect, Montreal represent a special case in terms of lower than average (Canadian) vacancy rates at around 0.7% (15). Also low rents and low home ownership rates, are discouraging construction of new housing, except for luxury condominiums (16).
Dweller-grower motivations & community participation
Urban gardeners in North American cities seem to engage in gardening activities more for pleasure and less for sustenance as compared to their counterparts in Southern cities. Most urban gardeners benefit recreationally from gardening, but one immediately notes that the garden can also act as an inter-generational bond with a large proportion of the elderly represented, as well as a (surprisingly maybe) large portion of moderate-income people growing food as an income subsidy. The economic value is an important factor to note in Northern cities, as well, because it helps strengthening community’s self-reliance.
Project Age-groups Income Motivations
6At grade > 55 yrs: 44% in 5 CAD 29-37K Food quality: >50%
City of Montreal out of 9 boroughs Leisure: 40%
Community Gardens > 45 yrs: 63% in 8 Ecology/quality of life 20%
out of 9 boroughs Repeat gardeners: 75% 7Rooftop 30 – 40 yrs. old. USD 200K Private access.
Green Roof, Luxury Decided to rent space
dwelling, New York because of garden.
Table 4: Gardener motivations by project and income
6 Per household 7 Per person
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