Cost Benefit Analysis about Green Roof for Developer - Coursework Example

Introduction Green roofs refer roofs that are either almost fully or partially covered by some form of vegetation. Green roofs design usual is such that there may be some technical layers in between the roof membrane and the vegetation including roof barrier, substrate, and drainage and water retention layers. Green houses are of different types depending on the vegetation used, the level of water that can be retained by the roof and the depth and quality of the substrate and the level of maintenance given to the green roof. Establishing the economic benefits of a green roof pauses a great challenge owing to the fact that the there is no direct economic terms of measurement and this means that there is need of using valuation methods for converting different types of ecosystem services (ES) benefits into monetary units. In green roofs present a situation where there is a public benefit while the costs are footed privately. Most of the benefits emanating from green roof are shared benefits and for a situation where there are no relevant policies in place the cost are private and are shouldered by real estate owners. The deficiency in policy, the end result is low supply of green roofs and low level of implementation than the optimal level from the socio-economic view point. The level of precipitation, the outdoor temperature and urbanization all have a positive correlation with ES value gained from green roofs meaning that location of a green roof is vital in the determination of the value. Urban systems highly depend on the ecosystem in the city itself and also that beyond it. The different urban systems as identified by Bolund and Hunhammar (1999) are stret trees, urban forests, wetlands, cultivated trees, lawns/parks, lakes/seas and streams. In the urban area the major issue is the ability of the area being able to a health and satisfactory environment for the dwellers. Living ecosystems have been pointed out as being vital when it comes to the well being of the dwellers with the acknowledgement of this ecosystems ability to enhancing the quality of life through reduction in noise, improved air quality and provision of recreational services (Niemelä et al., 2010). Many urban problems are generated with the same urban areas and usually having local solution gives the most effective way of dealing with these problems. Some of this problems are low quality air, urban flooding and heat island effect and with further increase in this problems expected as a result of climate change (Bolund and Hunhammar, 1999). Local low supply of various ecosystem services are seen to be the root of this problem. Roofs takes a substantial share of the horizontal surface of buildings but there has been low capitalization on the roof areas. Adding vegetation and providing growing substrate on the roofs results a development of an ecosystem which is able to provide services. A number of negative externalities can be mitigated by the ES of the areas occupied by buildings and can result to substantial reduction in the level of energy that is being consumed in the buildings (Oberndorfer et al., 2007). There is an opportunity for increasing the percentage cover of living ecosystems in urban areas through green roofs. But all said there is need to establish the extent to which green roofs are justifiable for compensating for the ground level ecosystems and to what level the green roofs can complement the ground level ecosystem bearing in mind that there is a substantial difference in terms of structure and in other functions. The challenge comes from the existence of trade-offs between the various ecosystem services and the interaction they have with the economic systems. A good example is where there will be improvement in the quality of air , the level of storm water retention and also the living environment of the inhabitants if there is increased share of urban green. But for a certain population size, to having a higher share of green area would translate expanding the total urban area, which would in turn translate to increased transport emissions or for the case where there are strict regulations in place it would mean having dense population outside green areas; resulting to major impact being felt on real estate costs (Conway et al., 2010). And putting all these trade-offs into consideration inclusion of green roofs to the green infrastructure portfolio is a very promising option, because with green roofs there is a chance of raising the supply of the ecosystem services which the negative impacts of lowering densities are avoided. When green roofing is done at a large scale, there are likely to additional spatial spillover effects. This means that the societal cost-benefit analysis resulting from green roofs , as a facilitator of different types of ecosystem services, may be effected as a comparison of the alternative roof solutions which may include conventional, solar and green roofs, meaning having a substitute of purely man made solutions with a combination of ecosystem services and some engineering. Benefits of green roofs Energy savings It is a big challenge when it comes to estimating the impact green roofs have with regards energy saving because each building, climates or green roof system will present a unique situation. The energy demand depends on the characteristics of the building which include the location, purpose the building serves and the number of floors. But focus can be directed to one building that has some specific properties , then the energy demand can be calculated in the current prevailing climatic conditions and then we can have prediction in future climate Such a simulation was carried out in the prevailing climatic condition in Finland by Jylhä et al. (2012) with the building codes being applied to the building. Through modification of the roof properties involving these simulations, one can be in a position of coming up with energy saving estimates which are achievable by green roof technology. The other ways is studying the cooling and insulation properties of vegetated roofs and making a comparison with the non-vegetated roofs (Seppänen, 2001). This approach is taken in the estimation of the savings on energy demand in heating while in the case of cooling there is use of the existing simulations and review of literature. Reduction in heat flux and solar reflectivity During the summer period it has been found that the exposed area for a block roof is found to rise to 80 ◦C for the case where the equivalent area beneath the green roof is at a relatively low level of 27 ◦C( FiBRE,2007). Cooling in green roofs is achieved through latent heat loss and improvement in reflection of solar radiation where the ratio of total reflected to the incident radiation is defined as albedo. According to Graffing (2005) the green roofs cooling is as effective as the cooling that come from the brightest possible white roof with albedo between 0.7 and 0.85 compared to that of bitumen roof whose typical albedo value is 0.1-0.2. It was established by Wong et al. (2003) through field measurement that when warm conditions are prevailing the heat for a bare roof accumulated during the day continued infiltrating the building at night. Green roofs were found to gain low heat amounts during the day thus reducing this effect considerably. Through measurement of air temperature at points of different heights above the green roof, it was revealed that upon sunset the air temperature above the vegetation reduced significantly and the cooling effect progressed even at night. On the other hand for the case of the hard ground there is reradiating of the stored heat, and this result to increased ambient air temperature. Lui and Minor (2005) did some investigation where two different green roofs each having 75-100mm of lightweight growing medium in Toronto with heat flux transducers being placed under the roof membranes. A steel deck having a thermal insulation and with no greening was used as a reference roof for comparison. Through measurements which were made it was established that the green roof resulted to saving in summer heat in the order of 70-90% for the summer while heat loss in winter was reduced by 10-30%. With thermocouples being placed at different depths in the structure, including in the room below the roof, there was reduction of the peak temperatures of the roof membrane and there was also delay from 2pm to 7pm. Figure 1 gives a comparison of the temperature profiles for the reference roof and a green roof Figure 1: Summer temperature profiles for a reference roof and typical green roof respectively. In the figure E0 is the temperature distribution for a thermocouple which was placed inside, E3 is for thermocouple that was placed under the waterproof membrane, E4 is for that placed under the growing medium which E5 is for that in the middle of the growing medium while OUT is for the outside temperature. It can be observed that apart from the temperature peak being delayed the value is also reduced. The temperature delay it appears to be attributable to thermal mass effect of the green roof while the increased layer of insulation available means only a small fraction of the heat flux reduction translates to internal temperature being reduced. For the case of winter the indoor temperature under the green roofs was found to be cooler in the evening time and morning times in comparison to the value in the reference roof, but this was attributable to the difference in the operational needs of the rooms under each roof. The difference in room operating conditions was not mentioned in relation to the summer results. A slightly higher heat loss during the day was found for the reference roof, by 1–2W/m2, which shows that the green roofs have reduced heat loss through the roof. Thermal mass Through addition of green roofs there can be improvement in the insulation properties of the building, and this would then translate to a reduction in energy consumption. Apart from reducing the heat lost from the building in the winter and reducing the amount of heat gain during the summer, the roof results to additional thermal mass that help in stabilizing internal temperature throughout the year. In the UK the building regulations requires that the U-Value of the roof is to be 0.25W/m2 K for dwelling houses and other buildings. However, there are some exemptions in the regulations when it comes to industrial activities. In the modern buildings, it is a must for good insulation to be provided, but the older buildings present a problem during the time of their building the current regulations were not in place. There was no insulation requirement for buildings in the UK until 1965, when a U-Value was assigned an upper limit of 1.42W/m2K in roofs (Szokolay, 2004). In 1976 this was reduced to 0.6W/m2 K in 1976 (UK Building Regulations, 1976) , with a further reduction to 0.35W/m2 K in 1985 (UK Building Regulations, 1985). What this means is that in the US most of the buildings have a lower insulation, and thus there can be assumption that additional insulation from a green roof would translate to increased energy savings for the less insulated building most of which are old. Knowing the thermal conduction properties of the roof structure material in place and also the thickness is important in determination of this effect. Energy demand for heating The impact of a green roof on the energy consumption of a building can be calculated by comparing the heat loss of different types of roofs, in other words by calculating how much a green roof reduces heat loss compared to non-vegetated roofs. In this way, we do not have to study the properties of the entire building. For these purposes we need data on the hourly temperatures from that region where the green roofs are supposed to be built at. For this purpose, we use observations from Kaisaniemi (in Helsinki). We selected years 2008 and 2010 of which year 2008 was unusually warm and 2010 in contrast unusually cold. The hourly heat loss q of the roof can be calculated with the following formula (Seppänen, 2001): Where U is the coefficient of thermal transmittance, whereby smaller coefficients means better insulation; where the unit for the quantity is  A is the area of the roof in   is the target temperature in the building given in K or C  is the hourly average temperature outside given in K or C For the case of a new building U is approximated to 0.09 and for a =vegetated roof the value could reduced to 0.08 (Jokisalo, 2012). As the building becomes older the insulation becomes, a good example being the case where the coefficient of a typical building that was constructed in 2005 is found to be 0.15. All said, here is need to have more research being undertaken on isolative properties attributable to green roofs so as to have estimates that are more reliable. Through summing up the heat losses on hourly basis of a roof and using the average of the warmer year and the colder year one can come up an estimate of the annual heat loss for each roof. And through subtraction it is possible to establish the impact of the green roof on the yearly heat loss of the building under consideration. in order to establish the green roof impact on the level of energy consumption it will further call for division of the reduced heat loss in conjunction with efficiency of the heat supply system and heat distribution system, eg 100% for the case of houses using electric heating system and 95% for the cases involving radiator heating (Finland’s Environmental Administration, 2012). After this one can proceed on to get the annual savings on energy consumption which can then be put into monetary savings through multiplication by the electricity price. The yearly savings are to be discounted for a period of 40 years which is the period that it is estimated that the green roof will be yielding benefits. For the case where a new building is involved using U =0.09) it will be found that the aforementioned settings total benefit of 3.33 €/m2 (of which 14 cents for the first year, real discount factor of 3%). On the other hand for the case involving a building that is old , build before 2005 where U is approximated to 0.15, an optimistic value for the case of an older building , the total benefit is found to be 22.86€/ m2. This shows that for the case of new buildings , there is incorporation of insulation measures , and in which case green roof has minimal impact in terms of energy saving. On the other hand in old houses insulation is poor and addition of green roof is likely to result to higher benefits in terms of energy saving. Energy demand for cooling In countries like Finland higher level of energy is required for heating the building that for cooling due to the prevailing conditions in the country. According to the results of simulation a residential one storey with a living area of 133m2 which is located in southern Finland has consumption of 3 kWh/ per year for cooling purposes with a slight increase to about 3.5 kWh/ in 2030. According to Saiz et al. (2006), there can be a reduction of up to 25% when a succulent drought resistant plant is used on a one floor building. And applying a discount of 3%, we have a benefit of 1.9 €/m2 floor where for the case of one floor building the value will be roughly the same for the entire roof. In Jylhä et al.( 2012) report, it was revealed that an office building will require more energy for cooling in comparison to what is required in a residential house from the same purpose. The energy demand was estimated at 7 kWh/ per year and it would increase slightly to 7.5 kWh/ per year by 2030. For the particular office building under consideration there would be a reduction of 10% in energy demand for cooling (Saiz et al. 2006) where there would be a benefit of 1.7 €/m2 floor. And considering a building having five floors this would roughly translate to 8.5 €/ m2roof Noise insulation The transmission loss of about 19Db will be achieved due to the ability of the green roof to reduce the sound reflection and improvement in soundproofing of the roof. The benefits from sound insulation are particularly important in the cases involving building located under flight paths or the building have very strong noise sources like in the cases of highways or nightclubs. In buildings affected by air traffic noise the improvement brought about by soundproofing may prove to be of great value. The most used technique for improving noise insulation is the use f plasterboards to serve as an extra ceiling element (Hedman, 1984). Based on information from Connelly and Hodgson (2008) the noise insulation benefits obtained from green roofs are close to or more than what could achieved by addition of some ceiling element. Bearing this in mind the cost of having an additional plasterboard on a roof is used in estimating the benefit of having a green roof. First is to have the price of plasterboard which can be approximated at 4 €/m2. The workload estimation for a building contractor is to be used in coming up with the installation costs. The estimation by a building contractor is that about 3m2 plasterboards can be installed by one person in an hour. In Finland a contractor is expected to receive 50 € for higher and with this put into consideration the total cost including materials and installation costs would come to 20 €/m2 . This can be taken be the highest noise insulation benefit estimate for a green roof and which is only applicable in the case of air noise zone. Emission regulation Use of vegetation has been established to be one way in which air pollutants in urban environment can be reduced. Air pollutants are reduced by the vegetation through passive filtration and airflows being directed and many pollutants being actively absorbed. However, as much as the vegetation has the ability to purify the air, the right choice of vegetation to be used is important since some tree species have been associated with release of volatile organic compounds that are harmful (Takano, T. et al. 2002). Quantification of the benefits it would require gas exchange data and the filtration capacity of the green roofs. This data is not available or is limited is supply. There have only been few studies in which removal of air pollutants by green roofs has been modeled. Field study findings by Tan and Sia (2005) have indicated that there can be a reduction of levels of particles in air by 6% above normal roofs while a reduction of 37% would be realized upon installation of green roof. This field measurement was a clear prove that installation of green roof can result to high improvement in urban air quality. According to the findings by Currie and Bass (2005) 109 ha green roofs in Toronto was capable of absorbing 8 metric tons of some air pollutant which were not specified in a year. Peck (2003) reported that the green roofing in Toronto which was covering about 6.5 millions m2 could reduce the concentrations in the air by 5-10% while the particulate matter could be reduced by 30tons. The study undertaken by Yang et al. (2008) on the performance of green roofs in Chicago , where it was found that 19.8 ha of green roof was responsible for removal of 1675kg of the air pollutants in the air in one year 52% of which being O3, while 27%, 14% and 7% of the uptake was NO2 , PM10, and SO2 respectively. The total amount of pollutants removed per year per hectare area of green roof was 85 kg. It was pointed out in the study that the removal of air pollutants by the green roofs depended on the concentration level of the pollutants, the prevailing weather conditions and growth of the plants. The month with the highest uptake was May while February had the least uptake. In making a comparison of their estimates with those of other studies Yang et al. (2008) established that their estimation was above those from Toronto (Currie and Bass, 2005) by 18%. For this study purpose we can use the gas reduction of 85kg of Yang et al. (2008) as a higher estimate while the 69kg of the Toronto(Currie and Bass 2005) estimate can serve as the lower estimate with regards to green roof gas uptake potential. The average costs associated with different type of emission were reported by Tervonen and Ristikartano(2011). In the calculations negative effects on health are put into consideration where focus is on cancer heart and lung diseases among others; then we have effect on environment and infrastructure where issues like corrosion are addressed and then we have climate change issues where GHGs come to focus. The cost estimation was undertaken separately for urban set up and for rural set up which is associated with sparse population. In urban setting the costs are found to be significantly higher this being attributed to the fact that in urban setting higher number of people will be affected. Table 1.1 Table 4.7. The costs of different gases and particles (originally for car emission calculations) (Tervonen and Ristikartano, 2011) With our main concern being with green roofs in urban setting, the estimate in second column of the previous table is to be used. In establishing the cost benefits, the obstacle is lack of cost estimates. However just as we have seen previously it is evident that there will be more benefits from green roofs for a highly populated area. In the table there has been calculation of the benefits on the basis of the empirical evidence with regard to uptake potential and then the total benefits have been calculated with the life cycle of the roof being put into consideration. In the table it can be seen there are no total air quality benefits in some of the gases but it is clear that the quantifiable benefits have a range of 4.8 €/m2 to 6.9 €/m2 as can be seen from table 1.2 Table 1.2 Cost estimates by industry survey Supplies of green roofs have given the cost estimates for installing a green roof on a low-sloping roof having an area of 500m2 and above. It is quite obvious that the size and the level of complexity of the green roof system will have considerable impact on the labor and the cost of the materials translating to more complex systems being much more expensive. We will consider a roof s that lie of a supporting structure where the cost estimates are to be based on the assumption that the roof is being built on an already existing building that is able to support a sufficient load capacity. Manufactured sheet of bitumen is to be used as the roof membrane and further cost are to be incurred if some part of the existing roof is to be removed. The standard cost of a standard bitumen roof can be approximated to 43 €/m2 inclusive of a rubber bitumen layer, waterproofing and cost of installing the roof. In the case where we are now considering installation with the purpose of having a green roof the cost will remain the same inclusive of any form of modification that are to be effected. The additional cost that comes at the stage of installing the green roof can be put at 62€/m2 inclusive of taxes. Sedum mats which is one of the important components accounts for about 53% of the extra cost and 24 % of the additional costs carters for installation costs while extra taxes will take the 23%. The green roof installation method that is least expensive would involve installation of a drainage layer, use of filter fabric soil and use of cuttings and seeds as the plant material. With these type of green roof there is freedom of having more diversified plant with the soul being deeper but it these would need a much stronger that can be able to support the weight of the soil. This green roof is found to be 20% cheaper in comparison to the green roof sedum mat system which is ready made , with the an extra cost in the range of 50 €/m2 tax inclusive. As indicated previously the costs are exclusive of structural modifications that may be needed by some buildings in order for the green roof to be accommodated. According to some study findings industrial buildings may have the structural cost being increased by up to 45% so as a green roof with a design load of up to 125 can be accommodated Green roofs with much lower load have been design and implemented in countries like Germany (Zinco,2012) , in Japan where we have the moss panel and in Switzerland. In UK the Green Roof Centre (2010) has given the estimation of between £60m2 and £100/m2 for extensive green roof system with the difference being brought about by specification and other variants such the installation being build or a retrofit. Some case studies that involved retrofitting in a number of public buildings in the city of Manchester courtesy of Jonas (2009) have been estimated at a total cost of £65/m2. This being the generic and initial estimations the actual cost may be lower. Alumasc which is a leading roof supplier in UK has given the cost of green to range between £50/m2 up to £150/m2 this being dependant on whether the old roof is to be stripped back so that it can undergo water proofing or whether the roof is already in good for direct overlay. The cost based on real green retrofit has been quoted at £120 and£180/m2 from Lambeth council data (Lambeth Council, 2009). The Bauder extensive system Ethelred estate, Kennington with an area of 4000m2 was constructed in 2005 at a cost of £716,000 which translates 179/m2. Another refurbishment undertaken in the Lambeth area is the Portland Grove with a total area of sedum roof of 961m2 with a total cost of £94,673 plus £20,300 scaffolding cost translating to a total cost of £120/m2. On the basis of a 60 year whole life costs the estimation by Lambeth Council indicated that they would pay 13% extra for incorporation of green roofs in comparison to when non-green roofs are to be installed (54). At prevailing prices of 2010 retrofit extensive green roof have been quoted at approximated cost of £150/m2. With regard to whole life cost analysis, Carter and Keeler (2008) puts the Net Present Value of green roof at 10-14% more expensive in comparison to conventional roof at a 60 year lifetime. They argue that incase there increased energy costs, or a decrease in construction costs of green roof or storm water was to become a bigger priority it would lead to green roofs being more economically attractive. They were also quick to note the positive social benefits that comes together with the planting of green roofs and that this need to be an additional incentive in decision making process. In Pittsburgh, US a comparative environmental life cycle assessment of green roof of 1115m2 was undertaken by Kosareo and Ries (2006). The assessment involved intensive green roof, extensive green roof and a conventional roof. The increase in roof life time by 45 years in comparison to 15 years control roof lifetime in addition to the change in thermal conductivity attributed to the growing medium brought about significant impact with regard to life cycle analysis. The conclusion which was arrived at was that even with the initial high cost, the energy and cost savings that were to be realized over the building lifetime translated to a green roof being a more environmentally preferable choice. This is seen to be a more favorable outcome with regard to green roof when compared to the findings by Carter and Keeler and highlights that the end results of life-cycle analysis for a green roof is dependent on the assumption that are to made in the calculation. Green roof cost-benefit assessments The benefits of green roofs are dependent on factors which may be grouped as the building, system and preference specific factors. The building specific factors focus on things such as type of use and number of floors; system specific factors look at the location of building in the city and the associated noise level while preference specific factors looks at issues like the extent to which the building owner appreciated the gain that comes with the green space. Usually the cost and benefits have are listed in the low scenario where we have high costs and low benefits and then we have the high scenario associated with low costs and high benefits. Additionally the most relevant factors will be listed and this are important in the determination of the scope of the benefits. From their analysis there is a revelation that in a green roof investment for the case of private decision maker then, it is justifiable when the personal preference of owning a building is very high. Conclusion From this report it has been seen that addition of green roofs to a building comes with a number of benefits. Building energy saving has come out very prominently where it has been seen that the annual heat and cooling loads can be reduced considerably. There are many studies that have been undertaken with the aim of assessing the extent to which green roofs can result to energy saving. However, the studies that have been undertaken have been seen to be lacking in definitive information with regards to roof structure thermal properties. What this means is that as much as the results usually will be positive with regards to saving energy, they will only be in the specific situation under investigation. The investigations giving U-Values for roofs with green roofs and those without, together with information on material build up and thickness, gives results that may be applicable in assessment of future design situations. In the report we have seen that older buildings are generally seen to be of less insulation and this means that a lot of saving can be made by addition of green roofs that for the case of new buildings. With a slow annual building turnover rate, making a difference in building energy use and addressing the issue of climate change , existing buildings could be retrofitted with green roofs. References Bolund, P.; Hunhammar, S. (1999) Ecosystem Services in Urban Areas, Ecological Economics vol. 29, pp. 293-301 Conway, D., Li, C.Q., Wolch, J., Kahle, C., Jerrett, M. 2010. A Spatial Autocorrelation Approach for Examining the Effects of Urban Greenspace on Residential Property Values. Journal of Real Estate & Financial Economics vol. 41, pp. 150–169. Niemelä, J., Saarela, S., Söderman, T., Kopperoinen, L., Yli-Pelkonen, V., Väre, S., Kotze, D. (2010) Using the ecosystem services approach for better planning and conservation of urban green spaces: a Finland case study. 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Analysis of the green roof thermal properties and investigation of its energy performance, Energy and Buildings 33 (7) 719–729. Jonas Deloitte (2009). Greater Manchester Green Roof Programme - Guidance Document. Tervonen, J., Ristikartano, J. (2010), Unit-costs of different cost elements in road traffic 2010 (in Finnish), Finnish Transport Agency, Liikenneviraston ohjeita 21/2010, Helsinki Takano, T. et al. (2002) Urban residential environments and senior citizens’ longevity in mega-city areas: the importance of walkable green space, Journal of Epidemiology & Community Health, vol. 56, pp. 913–916. Tan, P., Sia, A. (2005) A pilot green roof research project in Singapore, In Proceedings of Third Annual Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show, Washington, DC, May 4-6, 2005 FiBRE -Findings in Built and Rural Environments(2007). Can Greenery Make Commercial Buildings More Green? Cambridge University. Gaffin (2005). Energy balance modelling applied to a comparison of white and green roof cooling efficiency, in: Greening Rooftops for Sustainable Communities,Washington, DC. Washington State University (1993), Energy Efficiency Factsheet - Reflective Roof Coatings. N.H. Wong, et al.(2003). Investigation of thermal benefits of rooftop garden in the tropical environment, Building and Environment 38 (2) 261–270. Lui K. Minor, J. (2005). Performance evaluation of an extensive green roof, in: Greening Rooftops for Sustainable Communities, Washington, DC. Szokolay S.V. (2004). Introduction to Architectural Science: The Basis of Sustainable Design, Elsevier. The Green Roof Centre(2010). Cost of Green Roof. 26.01.2010, Zinco (2012) Zinco company homepages www.zinco.de Read More