2.1. Unit Values for Soundscape/Noise Changes
The current economic valuation approach to soundscape/noise changes is either a valuation per person change from annoyed to not annoyed (or vice versa) or per dB(A) change per person (or household/dwelling) per year [9
]. As a noise indicator the EU standard evening and night-time weighted equivalent noise level on the most exposed façade is used [17
]. Thus, for an improvement in sound quality one might consider an EU average of 20 EUR per dB per person per year [18
], or (assuming a household size of approximately two persons) 40 EUR per dB per household per year. Normally this type of valuation is applied to the noisier façade, not the quiet façade in the inner courtyard as is the case for our demonstration projects. Valuation experiments assessing human reactions to their sound environment predominantly target noise annoyance focussing on situations with high levels of transportation noise [9
]. The benefits of quieter areas and areas with improved sound quality, such as of restoration, restitution from physical and mental illness, stress relief, positive experiences, physical activity etc.
on health are not part of the valuation experiments. They are potentially important, but difficult to capture without appropriate complementary research approaches using other types of acoustic measures to assess the quality of the sound environment [20
]. A consequence is that current valuations are likely to underestimate the impacts from an adverse soundscape and fail to include benefits of good quality sound environments [21
An overview of the benefits of adopting a broader approach including contextual factors is provided by Lercher [23
]. Important nuances and differences in the overall exposure situation that are not reflected in the Lden
value of the most exposed façade should be taken into account. A challenge when valuing an improved soundscape at lower noise levels is that current approaches employ a high cut-off value. Improvements below the cut-off value are given zero economic value. As an example, all noise reductions below 50 dB(A) are regarded as providing no economic value [19
]. The rationale for using a cut off is that current valuation studies fail to detect significant differences in annoyance at lower noise levels. However, the lack of sensitivity to differences in human reactions may also be a result of the over reliance on a single indicator of the sound environment. De Kluizenaar et al.
, Öhrström et al.
, and Gidlöf-Gunnarsson et al.
found significant health, psychological and physiological benefits in asses to indoor and outdoor quiet sides [3
]. Amundsen et al.
found a shift in exposure annoyance relationships from having the bedroom at a quiet side to be equivalent to a 5dB noise reduction on the most exposed side [11
]. See Benfield et al.
for a study of the human-activity noise impact on the perceived soundscape quality in protected areas [26
]. In the CityHush project correction factors have been proposed to capture the impact of façade insulation, access to a quiet side, and an improved or noisy neighbourhood soundscape [12
], and a cut-off value of 45 dB(A) was employed, and assessed the improvement in the noise level on the quiet side to be 20% of that associated with a corresponding noise level reduction on the most exposed façade. Thus, a 10 dB reduction in the noise level difference between most and least exposed side is assessed to have the same effect on human reactions as that of a 2 dB noise reduction on the most exposed side.
2.2. Vegetation-Based Noise Attenuation Measures
Generally, in terms of acoustic benefit, vegetation affects the sound field in urban environments through three mechanisms: sound absorption and sound diffusion, which occur when a sound wave impinges on the vegetation and is then reflected back; and sound level reduction, when a sound wave is transmitted through the vegetation [4
]. Consequently, when vegetation is used on building façades the effectiveness of façade absorption can be greatly enhanced since there are multiple reflections. In build-up areas the absorption and diffusion effects are also useful for reducing the negative effect of reflections from the ground that often occur in outdoor sound propagation [7
]. Additionally, green roofs, particularly when installed on non-flat roofs, cause noise reduction of diffracted waves that intrude a street without traffic or a courtyard [5
]. For detailed description of impacts from green roofs and green walls, on locale climate, water management, energy use, etc.
, as well as particular challenges, see e.g. [31
2.3. Non-Acoustic Amenity Values of Green Roofs/Walls
The reviewed green roof/wall valuation studies are based on the use of the hedonic pricing method, where it is estimated how much dwelling characteristics impact on the property price or the rent [36
]. With data on sale prices of dwellings and the dwelling characteristics, e.g., location, living space, condition, number of bathrooms, etc.
(plus environmental characteristics), the dwelling prices are regressed on the set of characteristics, finding the percentage impact of the characteristic on the selling prices. The hedonic pricing studies on green roof/wall valuation do not mention noise/soundscape among the amenity benefits; they all stress the aesthetics (visual benefits) and mention either thermal or climate effects. Thus, although the noise/soundscape impact as part of the amenity value still cannot be ruled out completely, we may assume for simplicity that these value estimates omit noise/soundscape effects. Based on the country/city of the study, the year of the data collection, and the currency of the country, the original value estimates has been converted to Euro, and then simply updated to Euro 2010 values by the consumer price index (CPI). For property values, or the property value shares indicated from the studies, we applied a discount rate of 5% and a 50 year lifetime to calculate annuity values that are comparable to annual rents [37
]. The unit price estimate is simply the Euro 2010 value divided by the area of the measure, yielding a crude square metre value of the greenery. We relate this valuation to a household, that is, what a household will pay per year for an additional square metre of greenery. The valuations can easily be converted to Euros per person by dividing by the average number of people living in a household; the average number of people in each household in the 27 Member States of the European Union was 2.4 in 2008 [39
Peck et al.
described both green roofs and green walls, assessing the market possibilities in Toronto (Canada) [34
]. They assumed that these vegetation measures would yield the same property increase as “good tree cover”; and they stated a value increase interval for a property of 6–15%, thus a midpoint of 10.5%. For a Toronto house price of approximately CAD 230,000 in 1999, we calculated an annualised square metre value of green roofs and walls of approximately EUR 20 (2010 Euro value). This is the value accrued to one dwelling or household, not including possible external benefits for neighbours. Hunt does not differentiate between green walls and green roofs either, but states that: “The costs green upgrades add to a new home’s price vary widely. However, a 3 % to 15 % premium is a good rule of thumb” ([40
] p. 1). This interval has a midpoint of 9%, which would yield approximately EUR 18, applying the same residential values as for Peck et al.
]. Des Rosiers et al.
estimated that hedges, or green walls, added 3.9% to the property value, in their hedonic price study applying property data from the city of Québec (Canada) [41
Gao and Asami applied a particular kind of hedonic pricing of greenery, i.e.
, greenery of walls as well as greenery of streets and pedestrian spaces [42
]. They made estate agents value a set of dwellings in Tokyo and in Kitakyushu. The valuations were based on information about the sale prospects. Greenery quality scores were provided in addition to the street/landscape architecture attributes. For the aesthetic properties of walls they described three attribute levels: −1 for mostly concrete block walls, 0 for averagely greened walls, and +1 for continuously greened walls. Based on the pricing from the estate agents, they found that an increase in greenery quality level would increase land price by 1.4% in Tokyo and by 2.7% in Kitakyushu. If we assume 25 m2
as a green wall quantity approximation to (each of) the two quality levels (25 m2
greenery for level 0 and an additional 25 m2
greenery for level +1), the resulted unit value estimates is of, respectively, ca EUR 3.5 per square metre green wall in Tokyo and ca EUR 1 in Kitakyushu. Obviously, these estimates are very sensitive with respect to the area assumption.
Ichihara and Cohen found that homes in New York with green roofs had as much as 16.2% higher price than homes without green roofs [43
]. Relative to an annual rental price of USD 4,000, a unit value per square metre green roof of ca EUR 17 can be estimated. In this case the homes were apartments in three 24–27 floor buildings with 252–279 units, such that the aggregate value would be huge compared to the value for one household. Tomalty and Komorowski present value estimates for two types of green roof, a recreational rooftop garden and a “productive” rooftop garden (including vegetables/fruit) [44
]. For recreational green roofs they found a 20% property price increase, while for productive rooftop gardens they indicated a 7% increase. This study is from Toronto, but their estimates are also based on studies from other areas. It is possible to calculate that unit value estimates will be of, respectively, ca EUR 63 per square metre recreational rooftop garden and ca EUR 22 per square metre productive rooftop garden. Table 1
summarises the estimations for green roofs/walls.
Value estimates, per household per year, green roof/wall †.
Value estimates, per household per year, green roof/wall †.
|Study||Year Data||Country Data||Curr-ency||Property Price||Annu-ity||Gree-nery % Value||Gree-nery Value||EUR/ Curr-ency||CPI||EUR-2010 Gree-nery Value||Gree-nery Size (m2)||Unit Value (per m2)|
|Peck et al. (1999) ||1999||Canada, Toronto||CAD||230,000||12,599||10.50%||1 323||0.6313||1.25||1,044||50||20.88|
|Hunt (2008) ||1999||Canada, Toronto||CAD||230,000||12,599||9%||1 134||0.6313||1.25||895||50||17.9|
|Gao & Asami (2007) ||1999||Japan, Tokyo||JPY||602,400||32,998||1.40%||8 400||0.0082||1.25||87||25||3.46|
|2003||Japan, Kitakyushu||JPY||73,200||4,010||2.70%||1 980||0.0076||1.15||17||25||0.69|
|Ichihara et al. (2010) ||2000||US, New York||USD||73,024||4,000||16.20%||648||1.0827||1.22||859||50||17.18|
|Des Rosiers et al. (2002) ||1999||Canada, Québec||CAD||112,000||6,135||3.90%||239||0.6313||1.25||189||50||3.78|
|Tomalty & Komorowski (2010) ||2010||Canada, Toronto||CAD||395,460||21,662||20%||4 332||0.7325||1||3,174||50||63.47|
|2010||Canada, Toronto||CAD||395,460||21,662||7%||1 516||0.7325||1||1,111||50||22.22|
The mean of these value estimates is EUR 18.7 per square metre greenery per household per year, but the mean drops to EUR 12.3 if the highest estimate from Tomalty and Komorowski is removed. This would yield approximately 5.1 EUR per affected person (assuming a household size of approximately 2.4 persons). A 90% confidence interval from the household unit value distribution is from about EUR 3 to about EUR 60. Due to the relatively low number of observations these estimated average unit values are statistically uncertain and unstable. The estimates also depend on the assumptions regarding the size of the valued object, as well as other quality aspects that has not been possible to control for [34