The potential of building envelope greening to achieve quietness

Abstract

Reduction of noise is one of the multiple benefits of building envelope greening measures. The potential of wall vegetation systems, green roofs, vegetated low screens at roof edges, and also combinations of such treatments, have been studied by means of combining 2D and 3D full-wave numerical methodologies. This study is concerned with road traffic noise propagation towards the traffic-free sides of inner-city buildings (courtyards). Preserving quietness at such locations has been shown before to be beneficial for the health and well-being of citizens. The results in this study show that green roofs have the highest potential to enhance quietness in courtyards. Favourable combinations of roof shape and green roofs have been identified. Vegetated façades are most efficient when applied to narrow city canyons with otherwise acoustically hard façade materials. Greening of the upper storey's in the street and (full) façades in the courtyard itself is most efficient to achieve noise reduction. Low-height roof screens were shown to be effective when multiple screens are placed, but only on conditions that their faces are absorbing. The combination of different greening measures results in a lower combined effect than when the separate effects would have been linearly added. The combination of green roofs or wall vegetation with roof screens seems most interesting.Keywords urban sound propagation, green roofs, green walls, noise reduction, numerical simulations, road traffic noise 3 1.IntroductionThe use of vegetation has become an essential aspect in urban planning nowadays. In densely built-up city centers, building envelope greening is often the only possibility to meet this demand. These measures have many ecological advantages too, ranging from increasing the thermal insulation of the building envelope and reduction of urban heat island effects [1]- [9], acting as a buffer for storm water [9]- [14], improving air quality and increased carbon dioxide uptake [15]- [17], increasing urban biodiversity [18]- [22], providing a visually pleasant environment [23], to even crop harvesting. In addition, also from an economical point of view, building greening seem interesting [24]- [27]. Recently, the noise reducing possibilities of such building envelope greening measures have been identified [28][29] [30][31] [32].The presence of mainly acoustically rigid materials in cities (streets, bricks, concrete, glazings, etc.) leads to a strong amplification of the emitted sound from road traffic noise, and large sound pressure levels are observed in city canyons. The noise problem has indeed become one of the major environmental challenges in the urban environment. The WHO report "burden of disease by environmental noise" [33] quantified the many health-related effects by long-term exposure to environmental noise. The positive influence of quiet urban areas, as a possible mitigating measure, has been shown before [34][35] [36] and has become part of European noise policy [37]. As a result, the sound environment in poten...

Using natural means to reduce surface transport noise during propagation outdoors

“…[159], in both 2D and 3D, showed that green roofs have the highest potential to reduce noise levels at non-directly exposed façades. The road traffic noise reduction provided by a green roof strongly depends on roof shape [154,159].…”

“…[159], in both 2D and 3D, showed that green roofs have the highest potential to reduce noise levels at non-directly exposed façades. The road traffic noise reduction provided by a green roof strongly depends on roof shape [154,159]. In case of a ridge roof, the largest insertion losses were found (relative to the same roof shape but rigid), amounting up to 7.5 dBA as an average all over the courtyard (both along the courtyard floor and constituting façades; the courtyard height and width were both 19.2 m) (see Fig.…”

“…1), more specifically a 20-cm thick green-façade substrate [15] and a 10-cm thick semiextensive lime-stone based green-roof substrate [158], were used to numerically evaluate their potential in various inner-city road traffic noise applications [159]. More specifically, their application to urban courtyards (including courtyard openings) and urban squares has been investigated.…”

“…In addition, low-height noise barriers, covered with a green-façade substrate (see also Section 2.2.1), positioned near roof edges, were considered. Calculations were averaged over vehicle speeds ranging from 30 km/h to 70 km/h, for 4-lane traffic, with 95% light vehicles and 5% heavy vehicles [159].…”

“…In Ref. [159], green façades covering the lower half, the upper half or the full source or receiver canyons' façades have been investigated. The computed insertion losses depend on the assumed reflection coefficient of the reference case, e.g.…”