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Adapting Cities to Climate Change
The Implementation of Green Roof Infrastructures in Groningen
Abel Knipping, S2226065
Supervisor: E.M. Trell
Trilateral Bachelor Project, 16-06-2014
University of Groningen, Faculty of Spatial Scienes
Colofon
Bachelor thesis
Fase Final Version
Words 11,445
Theme Climate Change Adaptation in Urban Areas Title Adapting Cities to Climate Change
Subtitle The Implementation of Green Roof Infrastructures in Groningen
Author Abel Knipping
Studentnumber S2226065
Contact abel_knipping@hotmail.com
University University of Groningen
Faculty Spatial Sciences
Study Human Geography and Spatial Planning Mentor E.M. (Elen-Maarja) Trell
Place Groningen
Date 06-06-2014
1 Abstract
Increased precipitation, temperatures and droughts are problems facing us in the near future (IPCC, 2007) (Van den Hurk et al, 2006). Urban areas are vulnerable to changes in climate due to their density and population size. This thesis scrutinizes urban adaptation strategies to cope with these predicted problems offering tools such as: a change in materials, vegetation, water and built form. Special emphasis is put on green roofs as an adaptive tool to retain stormwater, to isolate and to bring a solution to the urban heat island. The construction of green roofs is not without thresholds, for example: most benefits of implementing them are public and not private. Economic incentives (direct or indirect) and technology or performance standards are used by municipalities to create an incentive for its citizens.
In Groningen the municipality uses a direct economic incentive in the form of a subsidy.
Results of analysing this form of policy are that there is room for improvement. Low income households and tenants are not reached with a subsidy and owner associations, responsible for the maintenance of a group of buildings, often throw a spanner in the works: reaching a majority in favour of green roofs in owner associations is hard. Recommendations that can be done to the municipality are to install an exemplary roof on an iconic building, the Forum for example and by doing so creating promotion and awareness for the subsidy.
Furthermore, subsidy targets should be set to make the goals clear and the occurrence and effects of heat stress in Groningen should be mapped and adaptation strategies should be implemented in the city’s hottest spots like Paddepoel. Furthermore the power positions in the market of green roofs are unequal and non-transparent, the knowledge gap between supplier and costumer is big. The municipality should offer guidelines and alternatives to assist citizens in making decisions between systems and the possibility to implement alternative systems like brown roofs for example should be considered.
Preface
This thesis is written as a final assignment for the bachelor Human Geography and Planning at the faculty of Spatial Sciences of the University of Groningen. The overarching subject of this thesis is the adaptation of cities to climate change but the thesis specializes in the implementation of green roofs within this process. It tries to give a theoretic framework on adaptation tools and on green roofs as a tool especially and further scrutinizes how the green roof policy of the municipality of Groningen is implemented and rated by its citizens.
I am indebted to several people that helped me during the process of writing this thesis. First of all I want to thank Elen Trell for her guidance and overall structure and help during this semester. Furthermore I would like to especially thank Luuk Smink for his contribution to conducting the questionnaire and to all the participants of my interviews: Anne Helbig (Municipality of Groningen), Klaas van Nierop Municipality of Groningen, Lammert Kamphof (Nijestee), André de Vries (Lefier), Henk Veenstra (owner of Veenstra daktuinen), Willem Bijleveld, Fransien Volgenant, Carla Veldhuis and Nynke van den Bergh for their constructive contribution to my thesis.
Keywords: green roofs, adaptation, climate change, policy
Table of contents
1. Introduction...5
1.1 Problem indication
...51.2 Problem statement
...61.3 Conceptual model
...61.4 Research questions
...71.5 Scope
...71.6 Thesis Outline
...72. Theoretical Framework...8
2.1 Urban design tools
...82.2 Green Roofs
...102.3 Benefits of Green Roofs
...102.4 Problems of implementation
...122.5 Policies to encourage green roof implementation
...132.6 Policy Development
...143. Methods...16
3.1 Used Methods
...163.2 Instruments for data collection
...173.3 Ethical issues
...194. Results...21
4.1 Context of research
...214.2 Dutch National Policies
...214.3 Groningen
...214.3.1 Motivation
...224.3.2 Opportunities
...224.3.3 Implementation
...224.3.4 Alternative policies
...244.3.5 Housing corporations
...254.3.6 Individual home owners
...274.3.7 Future of the subsidy
...285. Conclusion and discussion...30
Further research
...31References...32
Appendices...35
APPENDIX A Pictures
...35APPENDIX B Questionnaire
...37APPENDIX C Interview questions & Interviews
...381 1.
Introduction
1.1 Problem indication
Within contemporary literature the effects of the global warming on our cities have been widely discussed. The changing climate has severe effects on the world as we know it and asks for rigorous strategies to adapt and mitigate the effects of global climate change (IPCC, 2007). The Royal Dutch Meteorological Institution (KNMI) develops climate scenarios every 8 years. The most recent scenario shows the effects of climate change for the Netherlands. Our climate is predicted to be warmer resulting in milder winters and warmer summers. The winters will be wetter on average with higher extremes in precipitation and the summer months will have less days of rain, causing drought. But the intensity of summer precipitation will increase (Van den Hurk et al, 2006).
These changes, like increased temperatures and an increase in precipitation, will have an enhanced effect within our urban areas. One of the effects it enhances is the urban heat island (Santamouris, 2001). The Urban Heat Island (UHI) is a phenomenon in which a metropolitan area is significantly warmer than its surrounding rural areas due to human activities (see Figure 1). The heat stress this causes is a concern to the public health and will especially effect the
elderly, infant and ill population (Stott et al., 2007). A study of the Wageningen University (Van Hove et al., 2011) shows that even in a small city like Groningen the Urban Heat Island effect is present with a median of 1.5
oC and a maximum of 3
oC. Some of the following processes in a city cause this effect: short wave radiation is absorbed by low albedo materials, air pollution re-emits long wave radiation, and the evaporation from urban areas is decreased because of the less permeable materials present (Kleerekoper, 2011).
Furthermore the expected increase in irregular precipitation (Attema, 2012) will cause higher peaks in a city's stormwater runoff. Due to the built environment, infiltration functions are diminished and surface water runs off more quickly. If we want to deal with this change that implies changing the way we think about and plan/design our urban areas.
Gill et al. (2007) moot the solution of greening our urban space to react on the changing urban climate. Urban green space has a cooling effect on the urban environment and offers infiltration possibilities for stormwater. Especially in dense urban areas the competition for space is driving up the land values and due to this competition there is often little space available for conventional urban green spaces, like parks. Functions that don’t have direct economic value, ponds and parks for example, are considered inferior and are driven outside of the core economic areas. Roofs are a potentially unused space and offer a solution to the problem of space competition in urban areas. By implementing green roofs, unused potential
Figure 1. Urban Heat Island Profile (Lemmen, D.
and Warren, F. 2004)
Figure 2. Conceptual Model
square meters are given a purpose and can help in our adaptation to climate change.
1.2 Problem statement
Groningen is a city located in the Wadden-Sea area, facing the consequences and problems of climate change. The literature offers a set of tools to adapt to climate change, e.g. making urban areas greener (Kleerekoper, 2011, Gill et al. 2007), these will be elaborated further on in the thesis. This thesis investigates the possibilities and impossibilities of the implementation of green roofs in Groningen. The research compares different policy strategies for the implementation of green roofs and scrutinizes whether these strategies can have the desired effect in Groningen. Data will be gathered also by students from Bremen and Oldenburg to get an overview of green roof infrastructures and policies in the Wadden- Sea area. Their data can serve as a tool for policy comparison between Groningen, Bremen and Oldenburg if the corporation is successfull.
1.3 Conceptual model
The effects of climate change that are expected to play in the city of Groningen are visualised in Figure 2. To adapt to the changing climate, adaptation strategies offered by literature are elaborated and the implementation of green roofs in cities is further scrutinized in this thesis.
Green roofs can offer solutions to three of the expected changes, they retain stormwater and
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so help to prevent floodings due to increased precipitation (1), this retainment of water in the city’s ecosystem can play a factor in preventing drought (2). Furthermore they have a cooling effect on the environment due to which the urban heat island effect is mitigated (3).
Their isolating character is not only cooling the outside temperature but also the inside temperature of buildings, creating a friendlier living environment. Because there are financial and technical tresholds to overcome prior to the implementation of green roofs, governments have the task to encourage this implementation through a set of encouraging policies. This will eventually lower the treshold which makes it more appealing for individuals to construct green roofs and which will contribute to the cities ability to deal with the effects of climate change.
1.4 Research questions Main question:
To what extent do green roofs play a role in climate change adaptation and how are the municipal green roof policies and strategies of Groningen operationalized?
Sub questions:
- What are the risks and vulnerabilities of Groningen in relation to climate change?
- What tools can be implemented to adapt urban areas to the effects of climate change?
- What does the municipal green roof policy of Groningen entail?
- How are the municipal policies operationalized by citizens and housing corporations?
- To what extent are there possibilities to bring the private and public sector closer to each other?
- What are the differences in green roof policies and strategies between Groningen?
1.5 Scope
The focus on the municipal level is chosen because municipalities are responsible for the water management and benefit most from adaptation strategies like green roofs. A national framework will be necessary to understand the contexts in which the municipalities function.
1.6 Thesis Outline
In chapter 2, the theoretical framework, urban design tools are discussed and used concepts
are defined. Further emphasis is put on green roof structures and in the end desirable policy
constructions are presented. In chapter 3, Methods, the methodology of the thesis is
described: the forms of data collection are explained and accounted for. In chapter 4 the
collected data is analysed on the national and local level and answers to the research’s sub-
questions are given. In Groningen the collected data is categorised by three stakeholders: the
municipality, housing corporations and individuals. In chapter 5, Conclusion and discussion,
an answer is given on the Main question and the results are discussed. Furthermore
recommendations for further research will be given.
2.
Theoretical Framework
The expected effects of climate change are researched by the Intergovernmental Panel on Climate Change (IPCC). They expect changes in the frequency and intensity of extreme climate events and have very high confidence that daytime maximum and minimum temperatures will increase, accompanied by an increased frequency of hot days. Heat waves will become more frequent while the number of global frost days will decline. High intensity precipitation and the number of wet spills will increase at high and mid latitudes in winter, while the frequency of summer drought will increase (IPCC, 2007). As discussed in the introduction the Royal Dutch Meteorological Institute has developed a scenario for the Netherlands in which they conclude that the future will be warmer, with an increase in extreme precipitation (Van den Hurk et al, 2006). This new national scenario will be available in June 2014, but the most recent update from the KNMI concerning the Wadden Sea area comes from Attema and Lenderink (2014). In their report about the influence of the North Sea on precipitation in the North Sea area (<50km from the coast: including Groningen, Oldenburg and Bremen) they note:
‘’Despite the fact that the overall changes in coastal effect appear relatively moderate, impact on more extreme events could be considerable, increasing the probability of exceeding extreme thresholds by a factor two or more.’’
Extreme weather events will be of a higher intensity causing nuisance in both rural and urban areas located within a radius of 50 km from the North Sea. How can these areas adapt to these climate predictions? Climate adaptation has been described by Brooks (2003, p. 45 ) as ‘adjustments in a system’s behavior and characteristics that enhance its ability to cope with external stress’. Accordingly climate change adaptation will be defined as the way in which we enhance our ability to cope with climate change. This adaptation has to be done on many different scales and in consultation with many different stakeholders. The goal of mitigation strategies is not to be confused with those of adaptation strategies. Mitigation strategies focus on reducing the human impact on the climate, whereas practices of adaptation are to adjust the natural and human systems in response to the expected and actual climate change effects (IPCC, 2007).
2.1 Urban design tools
The literature offers several design tools to adapt to the effects of climate change in urban areas (Kleerekoper, 2011, Gill et al, 2007, Bowler et al., 2010). The tools can be divided into four categories: water, built form, material and vegetation. (Kleerekoper, 2011) The categories offer different opportunities to cope with climate change effects.
2.1.1 Water. Water bodies, such as canals or lakes, have a shown cooling effect on their
surrounding area during hot summer days (Robitu et al., 2004). This is caused by heat
absorption and evaporation, but as mentioned by Sugawara et al (2009) the fact that a water
body offers a free circulation path for the wind may be its most effective cooling
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characteristic. The cooling effect of the water body strongly depends on the water temperature in relation to the air temperature in the adjacent urban area (Van Hove et al., 2011). During the day a water body warms up, and when air temperatures decrease during the night water might have a reversed effect and warm its surroundings.
2.1.2 Built Form. Built form and geometry have positive and negative influences on an
urban climate. The shading buildings offer, cools urban areas but on the other hand buildings reflect and trap solar radiation, causing overheating. We can influence the built form, by implementing slanted roofs for example, and create optimal ventilation (Kleerekoper, 2011).
From a policy standpoint changing a city’s built form is rather difficult since the built form is not easily adjustable and adjusting it requires a lot of resources.
2.1.3 Material. Materials used in urban areas determine how the sun’s energy is reflected.
In low albedo materials short-wave radiation is absorbed which accumulate the heat (Kleerekoper, 2011). Several studies have showed that by increasing the albedo (reflection coefficient of a surface), temperature drops are observed (Doshi, 2006, Gaffin et al. 2005).
Synnefa et al. (2008) measured that a large scale increase in albedo decreased the heat island intensity in Athens by 1-2 ºC on average.
2.1.4 Vegetation. Vegetation exists in many forms. Mature trees have the ability to reduce the air temperature by providing shade and due to the fact that trees convert solar energy into latent energy through the evaporation of water. Most research about the cooling effect of vegetation has been done on the Park Cool Island (PCI). A park of only 0.15 ha had an average cooling effect of 1.5 ºC according to a study in Tel Aviv (Shashua-Bar and Hoffman, 2000). According to the meta-data analysis of Bowler et al. (2010), in which they reviewed all relevant literature available about the cooling effect of parks, parks have an average temperature which is 1 ºC cooler than non-green sites.
The research of Jones and Alexandri (2008) shows the potential of lowering urban temperatures by covering roofs or walls with vegetation. Green roofs in the hot and arid Riyadh, Saudi Arabia have shown the capability to decrease temperatures up to 12.8 ºC.
Green roofs showed to have a stronger cooling effect on the urban area compared to green walls because they can be implemented on a wider scale due to their lower price of implementation. Consequently green roofs have a greater effect on the urban scale as well (Alexandri and Jones, 2008).
The above mentioned design tools are very different in their characteristics. Vegetation has
high acceptance among citizens and is comparatively low in costs (Kleerekoper, 2011) a
characteristic not shared by the other tools. Changing the built form or creating new
waterways for example, are tools radical to implement and more expensive in nature. In
urban areas space is a scarce resource, which results in very high land prices and functions
like parks or big vegetated areas are driven outside of the economic core area. Roofs, and
walls, offer a solution in applying large-scale green areas within cities, but it is not that easy
to implement them. The benefits are high but to obtain these benefits costs have to be made by municipalities and private parties. Further negative effects of problems with the implementation of green roofs are discussed in paragraph 2.4.
2.2 Green Roofs
A common feature of green roofs is that they always contain a vegetation layer rooted in a substrate layer with a separate drainage layer underneath. (Mandema, 2008). Green roofs are generally characterized as ‘extensive’ or ‘intensive’ systems. The characterization depends on the planned usage for the area and on the plant material that is used.
Extensive roofs have a shallow depth of less than 15cm: they require minimal maintenance and are usually not accessible to the public. Due to their shallower depth plant species are limited to grasses, mosses and sedum: a drought-tolerant succulent. They are not heavy, weighing 20 to 150 kilogram/m
2, and have a water retention coefficient of around 50%.
Intensive roofs are deeper than 15 cm, have a water retention coefficient of 60% or higher, and can house landscapes also found at the natural ground level, trees and shrubs. They can be accessible to the public but also require more maintenance (FLL, 2002). Intensive green roofs weigh more than 150kg/m
2. With every extra cm of substrate a green roof’s weight increases with 15kg/m
2(van den Bergh, green roof owner). A research from Esha, a design consultancy company, (Mandema, 2008) in Rotterdam shows that 60% of the roofs can carry a weight of 180 kg/m
2. The situation of roofs in Rotterdam can’t be copied to the situation in Groningen without further local investigation, but it gives an idea of the possibilities and limitations extensive roofs in Groningen might have.
Figure 3. Cross-section of a representative extensive green roof system (Getter et al., 2006)
2.3 Benefits of Green Roofs
Green roofs have a multiple set of functions which are beneficial characteristics to climate
change adaptation. As Getter et al. (2006) mention: ‘Green roofs replace the vegetated
footprint that was destroyed when the building was constructed.’
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Stormwater retention is the most frequently cited and extensively studied green roof benefit (Banting et al., 2005; Hendriks, 1997; Obendorfer et al., 2007; Porsche and Köhler, 2003). On a conventional roof, water almost immediately runs-off, green roofs capture the precipitation in the media or vegetation and water will eventually be released back into the atmosphere by transpiration or will evaporate from the soil surface. Green roofs may reduce runoff by 60% to 100%
depending on the type of roof system (Moran et al., 2004; Rowe et al., 2003).
Mentens et al. (2006) have compared the data of stormwater run-off from 18 different publications and constructed the visualization shown in Figure 4. Here is shown that conventional roofs have an outflow of approximately 80% and extensive green roofs, which are most common, have an outflow of approximately 55%, intensive green roofs show to have the lowest outflow of aproximately 25%.
High intensity precipitation has been expected to occur more regularly in the future (IPCC, 2007), typically this stormwater is discharged quickly into the nearest water body or sewerage system. This can cause Combined Sewer Overflows (Carter and Rasmussen, 2008), resulting in untreated sewerage being discharged in local streams or rivers. Green roofs can prevent CSO’s by retaining significant amounts of stormwater (Doshi, 2006). Noted by Mandema (2008) and Getter and Rowe (2006) however runoff will still occur after the media is saturated, the time this takes depends on the thickness of the media layer. Green roofs can delay the runoff with 4 hours (Moran et al., 2004).Another social and private benefit provided by green roof systems is the thermal performance of the roof membrane. Green roofs can play an active role in cooling a city. This is partly due to an improved albedo. Whereas a conventional roof surface has an albedo ranging from 0.05 to 0.25 the albedo of green roofs ranges from 0.7-0.85 depending on the water availability (Gaffin et al., 2005). Green roofs also cool the city by evaporation, Gill et al. (2007) have calculated that an increase of vegetation by 10% can have a cooling effect of 4 ºC on street level. Green roofs also show to reduce indoor temperatures by 3 to 4 ºC when outside temperatures are between 25 and 30 ºC (Peck et al., 1999).
Green roofs furthermore provide an improvement in air quality by capturing common greenhouse gases CO
2and NO
xand dust particles (Peck and Kuhn, 2001). Many more public and private benefits of green roofs are present: the life span of roofing membranes increases
Figure 4. Annual outflow of precipitation as a percentage of the annual precipitation. Divided by type of roof: intensive green roof n=11, extensive green roof n=121, gravel roofs n=8 and
conventional roofs n=5. The outflow of water is never 100% because of evaporation. (Mandema, 2008)
due to the temperature moderation vegetation offers (Peck, 1999), there is an increase of biodiversity and habitat provision (Mandema, 2008) and noise can be reduced up to 6 dBm, depending on the location and the type of housing, due to the isolating function of green roofs. The aesthetic component of green roofs and the positive effect of vegetation on the sense of personal well-being and on urban livability is another benefit. There are correlations that show that when humans view green plants and nature it has beneficial health effects such as the lowering of blood pressure (Ulrich and Simmons, 1986).
A final noteworthy benefit is the fact that green roofs have been shown to affect the property value of the own, and nearby, real estate positively. It is marketable because it can help improve the environmental image of a company, Ford for example covered its entire factory, 10.4 acres, with a green roof (2003).
2.4 Problems of implementation
If there are so many benefits, then why are all our roofs not green yet? One of the main obstacles is the costs for the implementation of green roofs they vary greatly among sources consulted but are generally around €40-80/m
2and are highly dependent on the intensity/thickness of the green roof. A common rule that is notable in the pricing tables of major suppliers is: the more intensive the green roof the more expensive. Maintenance of a green roof is negligible (€1/m a year) and can be done by the owners themselves. Not only costs play a role but also a lack of expertise: in April 2013, a housing association in Groningen, Lefier, removed 20.000m
2of moss roof because there were parts blown off during a big storm. The thin green roof was installed in 2009 during a ‘renovation for sustainability’ (Dagblad van het Noorden, 2013). The planted moss didn’t strike root which left big parts of the roof bald of any vegetation and vulnerable to drought and wind (A. de Vries, manager real estate Lefier). This shows that not only costs play a role but also a lack of expertise and knowledge by local actors can impede a successful implementation of green roofs. It’s the role of municipal managers and green roof experts to overcome this knowledge gap.
Although the negative factors seem marginal, especially the costs of implementation are a big threshold for most individuals. Many of the benefits are shared with the public and are not internalized by the public owner: the owner is even making costs to create the public benefits (Ebbink et al., 2009). When public benefits are not fully realized by the party bearing the cost of the green roof installation, green roof policies are justified as a public intervention. More about possible municipal strategies and policies is discussed next.
Costs and benefits of green roofs
Conventional roof
Extensive green roof
Investment in roof per m2 € 15 € 40-80
Life span in years 20 60
Annual maintanance € 0,58 € 1,15
Figure 4. The costs and benefits of green roofs. Source:
www.sempergreen.com Retrieved on:14.5.2014
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2.5 Policies to encourage green roof implementation
If to rely solely on the goodwill of building owners, only direct private benefits will play a role in the decision making process, and green roofs will be less attractive to install compared to when the government distributes subsidies and legislation to increase the collective benefits green roofs have to offer (Kolb, 2008). This gap between private and public benefits justifies the development of municipal policies and regulations (Ngan, 2004). A few standards by which a government can stimulate and encourage its citizens are discussed in the following part.
2.5.1 Direct economic incentive
The most straightforward form of green roof policy is that of the direct economic incentive in the form of subsidies or direct financing. The subsidy should be linked to clear specifications about the quality of the green roof construction, such as minimum substrate depth, minimum vegetation coverage or maximum roof slope for example. Discussion exists about how high the financial support should be. Sometimes direct financial incentives target priority areas of a city. These are areas that are lacking in green spee for example. In downtown Munic greened retrofitted roofs gualify for a subsidy of €30/m
2, to a maximum of 50% of the cost (Landskron, 1998).
2.5.2 Indirect economic incentive
The main policy tool that is used to give owners an indirect financial incentive generally involves a lowering of stormwater disposal taxes. By separating the fee paid for sewerage and stormwater disposal the indirect incentive can be implemented. The amount of the stormwater fee is normally based on the total area and the proportion of the ground that is impervious. In Munster for example, installing a green roof along with other stormwater source controls reduces the amount of tax paid (Ngan, 2004). This gives building owners an indirect financial incentive to install a green roof with fewer sewerage overflows as a positive result. Another indirect incentive is allowing an increase in the building density when green roofs are installed on the building, a policy active in Portland where 1ft
2of bonus is allowed for each ft
2of green roof, if the green roof covers 30% of the roof area. If it covers up to 60%
2 ft
2of bonus is given and a coverage of more than 60% grants a 3 ft
2bonus.(Carter and Fowler, 2008)
2.5.3 Technology standard
A government can directly oblige buildings of a certain type to green a percentage of their
roofs, by mandating this in the building code. Candidates for this regulation are mainly public
buildings or large commercial buildings. On private buildings this regulation will have most
effect when implemented in the building codes for new development areas. Important is that
design specifications of the green roof are included to guarantee the desired green roof
quality. In the city of Basel, Switzerland new flat roofs and existing flat roofs over 500 m
2are
required to have a green roof of at least 10 cm deep and with native plant species
(Kazmierczak and Carter, 2010). In Tokyo, Japan the technology standard approach is also implemented: private buildings larger than 1000 m
2and public buildings larger than 250 m
2are required to have 20% of the rooftop greened (Carter and Fowler, 2008). 55ha of rooftops were greened within 2 years after the policy started. One of the main problems for this regulation is the protest it will evoke due to the obligatory costs people have to make.
2.5.4 Performance standard
Areas or sections of a city can be bound to tighter environmental controls and have to meet certain specifications based on stormwater management goals, urban greening requirements or rooftop reflectance values. These performance standards can take the form of a stormwater management manual which identifies the standards an existing or new developed area has to meet. A sophisticated urban greening policy known as the Biotope Area Factor (BAF) exists both in Berlin and in Malmö.(Carter and Fowler, 2008). BAF is defined as (ecologically surface-effective surface)/total land area. The higher the ecologically surface in an area the lower BAF will be. The target BAF is set by the municipality and are based on the type of land under development, whether construction is an extension of existing coverage or new and the amount of additional construction on the site (Carter and Fowler, 2008). A well-known American system of performance standards is the Leadership in Energy and Environmental Design (LEED) system where buildings are rated according to their sustainability. Green roofs directly earn LEED points through a variety of categories.
2.5.5 Other Policies
With the literature being so extensive on this topic the 4 most relevant policies were depicted and listed above. A short summary of other policies will be listed underneath:
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Ecological compensation measure: the landscape requires compensation for the loss of land due to new buildings. It targets specific locations where nature is about to get lost and, requires that the party causing impairment to natural functions is the one to pay for mitigation or compensation measures (Ngan, 2004).
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Media coverage and competitions: a more active promotion of the green roof industry will increase public awareness.
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Greening of public buildings: a municipality is responsible for being the perfect example. It can offer its citizens an exemplary green roof where they are informed about the possibilities and processes of a green roof implementation (Ngan, 2004).
2.6 Policy Development
Lawlor et al. (2006) suggest that there are six phases to a successful green roof policy
development:
1 Figure 5. The six phases in developing green roof policies (Lawlor et al. 2006)
1. Introductory and awareness: a municipality.looks.at the merits and environmental benefits of green roofs. Information is gathered by sending.delegates to green roof.conferences or by visiting another municipality.with existing green roof policies.
2. Community engagement: to gain.support for green roofs a green roof.committee is installed which may seek creative methods to raise.the public awareness. The committee.will outline the opportunities,.threats, strengths and weaknesses.of green roof development.
3. Action plan development and implementation: a green.roof demonstration project can be launched, green.roof tours and ongoing planning.meetings are essential. A review.of existing policy options and.tools is explored in this.phase.
4. Technical research: a research site is set up. A jurisdiction.exploring green roofs as a.step in setting green roof policy.needs local data that can be.applied as motivation. Researchers quantify the benefits of green roofs.
5. Program and policy development: this phase translates local research into policy options and tools. This involves establishing ways of offering incentives, financial incentives, tax credits or density bonuses.
6. Continuous improvement: the policy has matured and the jurisdiction decides whether to continue on the same path or explore other policy options. To gather information there must be a mechanism to collect and analyse feedback from users and professionals (Lawlor et al.
2006).
The steps listed above form a theoretical basis to analyse in which fase the municipality of Groningen is situated and concluding to that what steps have to be undertaken to create a successful policy.
3.
Methods
Research is done in a wide variety of areas and the purposes of each research are different and ask for different methodologies. Goals of the ‘pure’ research are to produce knowledge in order to better understand the world: this type of research is a continuum (O’Leary, 2010).
Contrasting to this are the goals of research that is conducted for the purpose of radical change of dominant structures (O’leary, 2010). The purpose of this research is a mix of the above mentioned. In the first place, it tries to produce and distil knowledge about green roofs and green roof policy in which it is pure. The knowledge collected will eventually be used to make a recommendation about ideal green roof policy and in that perspective this research promotes change.
3.1 Used Methods
Roughly two types of research are discussed by consulted methodology literature (O’leary, 2010): qualitative and quantitative research. Within quantitative research numeric data is statistically analysed, the main difference with qualitative data is that qualitative data consist of words and visual imagery, instead of numbers. This data requires a qualitative analysis.
The mixed methodology O’leary (2010) combines the two methods mentioned above in which the researcher either takes a quantitative perspective with the acceptation of qualitative data or a qualitative perspective with the acceptation of quantitative data (O’Leary, 2010). This research uses the latter mixed methodology, a qualitative perspective with the acceptance of quantitative data.
To answer my research question: ‘To what extent do green roofs play a role in climate change adaptation and how are the municipal green roof policies and strategies of Groningen operationalized?’ a mix of secondary and primary data is used (O’Leary, 2010). In the first instance mainly secondary data was used e.g. literature reviews and document analysis. This data provides me with a broad set of knowledge and skills to answer some of the research questions: e.g. what are the risks and vulnerabilities of Groningen in relation to climate change? To answer all the research questions however only secondary data will be insufficient. Primary data will be collected through interviews with stakeholders: e.g. green roof specialists, municipal representatives and public parties. This thesis uses qualitative research methods because of the context dependency of the research and the effort it makes to elicit value judgments from key stakeholders. These value judgments are hard to be interpreted by quantitative data, like questionnaires, and therefore interviews will be the main method of primary data collection.
A questionnaire will be used to gain inside in the awareness among citizens about the availability of a green roof policy.
3.2 Instruments for data collection
The following sub-questions were leading in the collection of data:
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1) What are the risks and vulnerabilities of Groningen, Bremen and Oldenburg in relation to
climate change?
2) What is urban greening and how can it be used as a tool to adapt to the effects of climate change?
3) What is the policy of the municipalities of Groningen, Bremen and Oldenburg concerning green roofs?
4) How are the municipal policies operationalized (within housing associations and individuals )?
5) To what extent are there possibilities to bring the private and public sector closer to each other?
6) What are the differences in green roof policies and strategies between Groningen, Oldenburg and Bremen?
3.2.1 Document Analysis
To elaborate the knowledge concerning green roofs and methods for a city to adapt to a changing climate a literature review is necessary. Most literature can be found on the internet and has been scrutinized and categorized. The thesis tries to compare the policy of Groningen to those in Bremen and Oldenburg. The information concerning the municipal policies will mainly be acquired through an analysis of municipal documents. This might become problematic for the German documents but in this case help will be offered by students from the universities of Bremen and Oldenburg.
3.2.2. Questionnaire
To investigate whether the citizens of Groningen are aware of the fact that a green roof subsidy is present a small investigating questionnaire was conducted by Luuk Smink within the shopping centres Paddepoel, Vinkhuizen and Wilhelminakade in Groningen. Participants will be asked a minimal amount of questions: for example whether they are familiar with the green roof subsidy, if they have a green roof themselves and if they will be more interested in the implementation of a green roof when the subsidy will be increased. 38 responses were yielded with a male/female rate of exactly 50%, 27 were higher educated and the response rate was high: 80%
3.2.3 Interviews
To elaborate the knowledge acquired from the available policy documents interviews were conducted with specialists, private parties and policymakers in Groningen.
According to Dunn (2005, in Clifford et al. 2010) there are three different types of interview.
These are: the non-structured interview, the semi-structured interview and the structured
interview. A structured interview has a set number of questions, completely opposite to a
non-structured interview. A semi-structured interview has as advantages that the answers of
the respondent are not completely guided by the questions asked, there is room for the
respondent to shed light on other relevant aspects that can be of relevance for the
researcher but were yet unknown. This flexibility is not present in structured interviews and
overrepresented by non-structured interviews. The interviews conducted in this research
were all semi-structured: some of the key-questions will be answered but since the thesis is exploratory in its fundaments room for new insights is left open. Important to note is that unlike with most questionnaires, ‘the aim of an interview is not to be representative but to understand how individual people experience and make sense of their own lives’ (Valentine, 2005). Some main reasons to make use of an interview are listed below:
1. To analyse the complex behaviour and motivations of persons.
2. To measure the difference of opinions and experiences between persons.
3. To collect data (qualitative) that cannot be produced with the help of other methods.
4. An interview shows that there is respect for the interviewee whom can also expect a form of reflection on their ideas.
The disadvantages of interviews can include: little anonymity for the respondent, the difficulty to have access to respondents and the danger of influencing the respondent by asking leading questions.
When conducting an interview a few factors are essential. One should be prepared down to the last detail and know everything about the topic when conducting the interview. Open questions play a key role in a good interview, this way you keep the information flow going and avoid short answers. A final key factor is that the interviewer should be listening precisely, this way you can pick up interesting side stories. By only finishing a list the interview will be less dynamic and probably less fruitful as well. The interviews are constructed in a pyramid structure, which means that they start with some basic questions followed by more constructive and profound questions (Clifford et al. 2010).
3.2.1 Interviewees
Some of the key actors with whom I want to conduct interviews are listed underneath but first it has to be stated that the interview design necessary, is very dependent on the stakeholder being interviewed. The research tries to shed light on the process of green roof policies from the private perspective as well as the public one. Both sides have their own situational characteristics and own expertise of the topic, due to which questions cannot be simply copied to the next interview.
Firstly to expand the knowledge I elicited through a literature review I conducted an interview (Appendix C with a green roof specialists in Groningen. Henk Veenstra, owner of Veenstra Daktuinen started his company in 1999 and has constructed many green roofs in Groningen and the rest of the Netherlands.
To expand the knowledge about the municipal policy, interviews (Appendix C) were
conducted with Anne Helbig from the department of policies and design of the municipal
spatial planning department and with Klaas van Nierop, urban ecologist within the
municipality of Groningen. They helped to shed more light on the situation in Groningen and
the incentives for municipal policies.
1
Nijestee and Lefier, major housing corporations in Groningen, were willing to show their perspective on the implementation of green roofs in Groningen.
Willem Bijleveld, contacted due to his performance in a green roof promotion video of the municipality, showed how policies are perceived by citizens since he is a green roof owner himself. More interviews with green roof owners where conducted with: Carla Velthuis, Fransien Volgenant and Nynke van den Bergh. They were all reached by using the snowball method.
Date Name Place/institution Category Time
16-04- 2014
Henk Veenstra V. Daktuinen
Telefonisch
Specialist 17.00
08-04- 2014
Anne Helbig ROEZ Municipality
Water manager
11.00 16-04-
2014
Klaas van Nierop ROEZ Municipality
Urban ecologist
15.00 14-04-
2014
Lammert Kamphof NIJESTEE
Damsterplein
Housing Corporation Green architect
13.00 08-05-
2014
André de Vries LEFIER
Zuiderdiep
Housing Corporation Real estate manager
11.00 14-04-
2014
Willem Bijleveld Thuis Green roof owner 15.00
06-05- 2014
Fransien Volgenant Zernike Green roof owner 12.00
06-05- 2014
Carla Velthuis Thuis Green roof owner 17.00
06-05- 2014
Nynke van den Bergh Thuis Green roof owner 17.45
Table 1. Interviewees
3.3 Ethical issues
All interviews will be conducted within a location appointed by the interviewee. With W.
Bijleveld for example an interview in his house was arranged. By meeting the respondent in a, for them, familiar environment you create an informal and casual atmosphere in which the gap between me, the researcher, and the respondent is minimalized (O’Leary, 2010).
When conducting an interview you will have to be cautious and always consider your
‘positionality’. You will have to be aware of certain existing power relations, in which you as a
researcher have to be the neutral party. Self-evident you should always guarantee full
confidentiality and anonymity (unless the respondent desires otherwise) to the participants
of your research and treat their opinions with respect. Furthermore participants have the
right to withdraw from the research at any time without explanation. It is also common to
provide participants with a summary of the research results (Clifford, 2010). All respondents
to my interviews will receive a copy of the final results.
4.
Results
4.1
Context of research
T
he research has its main focus on
Groningen but strives to compare the
1
findings in Groningen to the cities of Oldenburg and Bremen. Therefore a description of the local contexts will be necessary.
Groningen
Groningen is the seventh largest city in the Netherlands and the biggest city of the north with 198.108 citizens (CBS, 2014). Groningen is famous for inhabiting a large amount of students, around 50.000, and is considered to be voting mainly left-winged. Another interesting detail is that Groningen was voted as the greenest city of the Netherlands in 2013 by Entente Florale (Gemeente Groningen, 2013). Although the competition only incorporated 9 municipalities Groningen is promoting its green characteristics actively. The university for example has set the goal to become the greenest university in the Netherlands.
4.2
Dutch National Policies
The national government of the Netherlands does not offer any green roof subsidies for individuals. Only for companies there are possibilities to receive a tax deduction when installing green roofs through the Milieu Investerings Aftrek (MIA) freely translated the Environmental Investment Deduction, the deduction is not valid for non-profit organisations, municipalities or individuals (Mandema, 2008). It is remarkable that the Netherlands is so far behind on this matter if you compare it to its neighbouring countries like Belgium and Germany (Ngan, 2004). There are national regulations concerning the water management and climate adaptation within cities but they only offer tools and no restrictions. The power to intervene and to adapt urban municipalities lies with the water boards and the local governments (Helbig, water coordinator Groningen)
4.3
Groningen
In Groningen, as of March 2008, the first green roof subsidy in the Netherlands is available for individuals. Companies can apply for the subsidy as of 2010. The municipality subsidizes
€30/m
2for 6-100 m
2. When the surface is bigger a downgrade sliding scale is triggered with a subsidy of €20/m
2for 100-250 m
2and €10/m
2for 250-1000 m
2. At the start the subsidy was financed out of a municipal sustainability fund. To continue with the green roof policy a new source of financing had to be installed when the sustainability fund ran out in 2010. This new financing came out of the sewer taxes, good for 13.6 million euros a year based on 100.000 connections of €136 a year (Helbig). In contrast to Rotterdam where the water boards finance 20% of the subsidy, the subsidy in Groningen is fully paid by the municipality.
Anne Helbig: ‘The water board endorses the importance of green roofs but this has no financial consequences.’ Looking back at the model of Lawlor et al. (2006) Groningen is currently in phase 6, a phase of continuous
improvement and reflection on the earlier stages of research and policy development.Figure 6. Groningen
4.3.1 Motivation
In Groningen two types of sewerage systems are present: combined and separated sewer systems. Within the combined systems, which cover 80% of the city, rainwater and wastewater are drained together. To prevent a CSO, which will cause wastewater to infiltrate in groundwater, it is beneficial to slow rainwater down in the draining process. Because of the desire to keep the city compact (Gemeente Groningen, 2009), the city densifies and petrifies which causes a decrease in infiltration capacity and an increase in flooding risk.
Green roofs are seen as a helpful tool within water management and that is the main incentive of the municipality to subsidize their implementation. Because of the green roofs water will be retained on the roof itself and discharged with a delay or not discharged at all because of evaporation (Moran et al. 2004). Other municipal motivations to subsidize green roofs are their contribution to the local ecological systems, the aesthetic aspect of green roofs, their contribution to the liveability and the cooling effects green roofs have on the city (Helbig and van Nierop, municipality of Groningen).
Helbig (water coordinator Groningen) notes: ‘[B]ut the background of watermanagement is the most important reason of this subsidy because we note that financially. Retaining water overground is cheaper compared to retaining the same amount underground.
4.3.2 Opportunities
To estimate the opportunities of green roofs in Groningen a dataset of flat roofs is needed.
Stefan Hermans a graduated Engineering student of the Hanzehogeschool, concluded that 175.000m
2of flat roof surfaces are located in the inner city of Groningen. Not all of these roofs qualify for bearing the weight a green roof has, Hermans estimated that 59% of these roofs or 103.250m
2is constructed to bear the weight of an ecological roof: 98 kg or more, an estimation of the roofs that could bear the weight of a normal sedum roof has not been made but is obviously higher. Herman based his estimation on data acquired in Rotterdam by Esha: a design consultancy company (Hermans). In their study they concluded that 59% of the roofs in Rotterdam could bear the weight needed for an ecological green roof.
4.3.3 Implementation
According to the most recent available data, September 2011, there were 180 green roofs realized within the city of Groningen, covering 55.000 m
2(van der Brug, 2012). Their location is shown in Figure 9. The green dots are private green roofs and the purple dots are those roofs
placed on companies.
Unfortunately no recent data
was available to upgrade this
map. The available subsidy has
been €500.000 in the years
2008, 2009, 2010 and 2011 only
51% of this available subsidy,
1
€255.000, has been used in that period, realizing 12.000 m
2of green roofs. The other 43.000 m
2, 30.000 m
2was realized with incidental contributions of the municipality: 20.000 m2 in Lewenborg for example and 13.000 was realized without financial contributions of the municipality.
Figure 7 shows a certain concentration of green roofs in the centre and south sides of the city. An interpretation/explanation can be that in those areas the amount of owner-occupied housing is relatively high. Van der Brug (2012) notes that the green roofs are mainly located around the Hondsrug, a ridge of sand, where the precipitation outflow goes rather fast and where there isn’t much surface water for the precipitation to flow into. This fact is beneficial for the water management of the city, but the municipality is not promoting their subsidy more actively within these desirable neighbourhoods.
4.3.3.1Problems of implementation
First of all the effect of involving companies has been less than expected, businesses were involved when the subsidy started to be financed through taxes but not as many businesses as expected have made use of the subsidy. Probably because the roof structures of industrial areas are not strong enough for an extensive installation of green roofs (Helbig). A second problem is that a municipality has limited power on the processes in the field:
"We cannot oblige, we can only encourage, promote and educate (van Nierop)."
Thirdly, the development of a new building involves a lot of parties, actors that are usually involved within one development are: the architect, the developer, the owner and the municipality. All these parties will have to be in support of the idea to implement a green roof, often creating difficulties when one party is obstructive (van Nierop, urban ecologist). A last problem inhibiting green roof constructions is the historically low construction activity.
As noted the best moment to implement a green roof is on a new building. Van Nierop notices a change in the green roof trend:
‘’[O]n most new building projects green roofs are realized, in contrast to five years ago when you really had to convince and persuade.’’
Awareness might be another problem of implementation. Transferring knowledge about green roofs and green roof policies to the public and creating full awareness is difficult. The questionnaire showed that 34.2% of the respondents are not familiar with green roofs.
4.3.4 Alternative policies
4.3.4.1 Direct financial incentives:
The direct financial incentive is implemented in Groningen at the moment through a green roof subsidy. In Groningen this subsidy is €30/m
2but the amount varies greatly among
Figure 7. The dispersion of green roofs within the city of Groningen (vander Brug, 2012)
municipalities with a green roof policy. On average green roofs cost €60/m
2, but this is highly dependable on their intensity. Klaas van Nierop states that when the subsidy in Groningen would be increased there will be too many benefits for the users of the subsidy:
implementing a green roof will save money compared to a conventional roof because of lower maintenance costs and municipal money will be spent wrong. The operationalization of the direct financial incentive will be scrutinized further on in the thesis, since it is not an alternative to the contemporary policy.
4.3.4.2 Indirect financial incentives:
The main policy tool for an indirect financial incentive involves the lowering of stormwater disposal taxes (Ngan, 2004). But the system in Groningen does not know this kind of tax and there is no relation between the amount paid and the degree of petrification. Everything is bundled in the sewerage tax of €136 per connection and it is possible that multiple households are connected to one sewerage connection. Lowering this sewerage tax when a green roof is installed is a possibility but the amounts saved are too small to give a decent stimulus (Helbig, water coordinator Groningen). The municipality has researched the possibility to install a tax dependable on the amount of hard surfaces present in the area, but came to the conclusion that they couldn’t make the tax high enough to offer a good stimulus (Helbig). Concluding we can say that the indirect financial incentive is no viable policy in Groningen.
4.3.4.3 Technology standards:
A government can directly oblige owners to construct a green roof. On private buildings this regulation will be most effective when implemented in the building codes for new development. Anne Helbig’s reaction to this policy:
‘’ [W]e don’t want to prescribe too much. We prefer to stimulate and facilitate instead of imposing it directly.’’ Besides this fact, directly obliging home owners to install a green roof is not permitted by national laws and regulations. This type of policy is most often used in metropolis where the urge to reduce the urban heat island effect is high (van Nierop, urban ecologist). In Groningen it’s not the desired policy but it might be an idea to implement a certain set of rules, focused on green roofs, instead of recommendations within building codes for new buildings.
4.3.4.4 Performance standards:
Sections of a city can be bound to tighter environmental controls and have to meet certain
specifications. These targets are set by the municipality and are based on the type of land
under development. In Groningen there are certain norms that look like this. In case of new
development, the amount of green in the developed area will have to stay the same and if
this is not feasible this should be compensated by greening an area outside of the developed
area (Kamphof, manager public space Nijestee). When building and increasing the amount of
impermeable surfaces it is a rule that 10% of the new area should be water, called the
watertoets (Helbig). Though not including greenery in this rule it does help preventing
flooding and cooling the area.
1
Permits and zoning are good tools for implementing performance standards. Another example of that is the Energy Performing Coefficient (EPC). The EPC is an index that represents the energy efficiency of buildings: a completely passive house without energy needs has an EPC of zero. A national guideline is set on an EPC of 0,6 and it’s expected to be set on 0,4 in 2015 (Kamphof). Green roofs contribute to a lower EPC and by a lowering of the EPC level an increase in green roofs can be expected.
4.3.5 Housing corporations
This thesis is trying to shed light on the way green roof subsidies are operationalized and an important aspect of that is the perception of the subsidies by its target groups. A separation is made between two target groups namely tenants, represented by the housing corporations Nijestee and Lefier and individual home owners. Within the green roof policy tenants are a vulnerable group: they are more flexible and might be feeling less responsible and attached to their homes, having less incentive to install a green roof.
4.3.5.1 Operationalization of the subsidy within housing corporations
Both housing corporations, Lefier and Nijestee, have the responsibility to design the space surrounding their buildings. The way they do this is captured by municipal rules and laws.
They are not allowed to remove any green or water but if destruction of green is necessary they will have to construct a green zone somewhere else. Furthermore within new developments 10% of the surface will have to be water, if impossible this water can be constructed somewhere else within the city (de Vries). Kamphof notes that a good public space leads to less destruction, happier tenants that tend to move less and live longer on the same place.
The general reaction of housing corporations on the green roof policy of the municipality is positive, but some question marks are placed. Lammert Kamphof, manager public space at Nijestee has his doubts concerning the contribution of green roofs to cooling the city.
‘Hotspots are not caused by a small roof but in particular by building volume.’
Kamphof sees more merit in green facades but also admits that their implementation is even more expensive and probably not viable. André de Vries real estate manager at Lefier, notes that the main interest of the green roof subsidy lies at the municipality, smaller sewerage systems and less ‘clean water’ that is unnecessarily purified is what he sees as the most important thoughts behind the subsidy.
De Vries mentions that green roofs can offer a solution to reach the municipal greening goals
when Lefier densifies an area. This makes the green roof constructions of housing
corporations seem to be driven out of necessity or marketing ideas instead of ideology. This
is mainly due to their smaller financial space and their changing role: five years ago green
roofs were implemented more easily (de Vries). Governmental legislation obliges housing
corporations to contribute a large amount of money to the government to account for the
housing benefits, starting in 2017 (de Vries).
The above is mainly a conclusion about green roofs constructed top-down from out of Lefier, but tenants themselves can still request a green roof. The owners will have to pay for the green roof themselves, but they have to ask permission from Lefier. According to de Vries this has never happened before at Lefier. The reason why Lefier does not contribute to a construction financially is mainly out of the principle of equivalence: if they grant one tenant with the right to construct a green roof with their contribution they will have to do this for everyone else as well which creates an unfeasible situation.
At Nijestee the roles are distributed a bit differently. In general most of their green roofs are implemented by the architect or by Nijestee and planned top-down but they try to work on invitations of tenants more and more. After a tenant’s request Nijestee will inspect the roof structure and estimate the life expectancy of the roof. A roof that has to be replaced within 3 years will not be eligible for a green roof construction, but when an application is granted tenants are free of costs and Nijestee will pay for the green roof. Kamphof says: ‘The eventual municipal subsidy is nice but no strict necessity to start the project or not.’
Most of their green roofs are located on visible locations, in that way you ‘kill two birds with one stone’ (Kamphof). It is not only sustainable but also aesthetic, a non-visible green roof is not common and green roofs on every roof are impossible: ‘it’s just too expensive’ (Kamphof and de Vries).
4.3.5.2 Future
With the construction sector in the doldrums de Vries (real estate manager Lefier) is not expecting a big increase of green roofs at Lefier: ‘Look, we are going along with it, but we are not going to make additional investments.’
On one of their new buildings a green roof was constructed to compensate for the petrification of the area. But the implementation of a green roof is very much dependent on the context and the type of project. Because the tenants of Lefier are fully financially responsible for the implementation of a green roof an increase in ‘private’ green roofs should not be expected. As de Vries noted they have never had an application for a green roof from one of their tenants.
At Nijestee Kamphof expects the amount of green roofs to increase within the next few years. ‘It makes tenants happy, what we can do is help and give an active contribution.’
The organisation structure within housing corporations can be very hierarchic and conservative hindering the organisation to act transparent (Veenstra). The departments all have their own preferences. Veenstra, a constructer of green roofs and considered a specialist on the topic, notes that: ‘I have the idea that the department of maintenance sees green roofs as a good long-term investment but the Rental department doesn’t want to convert the costs into the rent. They only implement green roofs when the architect proposes to do so.’
Kamphof admits that the collaboration between departments is not always ideal, but
Nijestee is working on it. At the moment the department of Maintenance is remembered to
give a notification to Development and Residential Affairs when roof structures have to be
1
replaced: the ideal moment for a green roof. Furthermore Nijestee awaits the initiative of its tenants, it’s up to them to decide how much green roofs will be constructed on Nijestee buildings in the future. Kamphof : ‘That will not be thousand square meters a year, perhaps a couple of hundred meters.’
4.3.6 Individual home owners
In the conversations conducted with individual home owners who have a green roof their motivation for the construction of the roof and their opinion about the subsidy of the municipality was elicited.
4.3.6.1 Motivation
The motivations of individuals to construct a green roof are quite similar. Overlapping motivations were: a better view and the contribution of green roofs to a better urban environment. Volgenant about green roofs and sustainability: ‘It is a route that we, as residents of planet earth, will have to start walking.’ It can be said that all four respondents implemented a green roof on top of their home or shed out of ideology. Veldhuis and van den Bergh noted that they would have implemented a green roof also when no municipal subsidy would have been available: their roofs are shown in figure 8.
Both had around 10m
2constructed on top of their sheds with the total costs lower than €500.
Because of their pitched roofs a bigger surface of green was impossible. For Willem Bijleveld
and his VVE (owner association) the subsidy of the municipality was a decisive factor.
Together with 9 other building owners they implemented a green roof in 2008 with the total surface of approximately 450m
2and with the costs of €17.000. The main reason why they decided to construct a green roof (Figure 9) was the heat problem on the top floor in the summer months. Bijleveld notes: ‘Well, when the subsidy would have been absent I am not sure if the roofs would have been constructed.’ In the end the municipality took a share of 60% of the total costs. Bijleveld furthermore remarks that the temperature decrease on the upper floor is significance but not as desirable as expected.
Figure 9. Green roof of Willem Bijleveld Figure 8. The green roofs of van den Bergh (left) and Veldhuis. Source: Abel Knipping
