Influence of rainfall on the noise shielding by a green roof

Renterghem, Timothy Van; Botteldooren, Dick

doi:10.1016/j.buildenv.2014.07.025

Cited by 17 publications

(16 citation statements)

References 29 publications

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“…Long-term in-situ experimentations were also conducted on green roofs incorporating relatively heavy substrates to evaluate the variation of acoustic signal attenuation with substrate water content. Van Renterghem and Bottledooren reported variations reaching 10 dB between dry substrate and moistened substrate close to saturation in the 250-1250 Hz frequency range [20]. Liu and Hornikx performed similar experiments for two roofs incorporating different substrates [21].…”

Section: Introductionmentioning

confidence: 90%

Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes

et al. 2021

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Section: Introductionmentioning

confidence: 90%

Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes

et al. 2021

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“…A long-term in situ diffraction experiment 34 near the edge of a building equipped with an extensive green roof, subject to natural precipitation, showed that sound propagation was mainly sensitive to the volumetric water content (VWC) of the substrate in a particular frequency range, namely between 250 and 1250 Hz. 34 The difference in the noise attenuation between 10% VWC (relatively dry state) and a fully saturated condition ranged up to 10 dB. 34 However, the impact of the substrate's water content on the overall A-weighted road traffic noise abatement was predicted to be rather limited (less than 1.5 dBA).…”

Section: Measurementsmentioning

confidence: 99%

“…34 The difference in the noise attenuation between 10% VWC (relatively dry state) and a fully saturated condition ranged up to 10 dB. 34 However, the impact of the substrate's water content on the overall A-weighted road traffic noise abatement was predicted to be rather limited (less than 1.5 dBA). 34…”

Section: Measurementsmentioning

confidence: 99%

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Improving the noise reduction by green roofs due to solar panels and substrate shaping

Renterghem

2018

Building Acoustics

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The urban fabric largely consists of acoustically rigid materials. This not only affects sound pressure levels in streets, but also how sound propagates towards the back side of a building or to connected urban canyons. A green roof is a practical solution to have roof absorption, mitigating diffracting sound waves. Flat green roofs were shown to provide roughly 3 dBA urban road traffic noise reduction relative to a common flat rigid roof. Although already relevant, it has been numerically studied in this work how the green roof insertion loss of flat roofs can be further increased. Solar panels on green roofs were found to significantly decrease sound pressure levels at the shielded building facade, up to 5 dBA on top of the insertion loss of granular substrates. Polyurethane foam slabs as green roof substrates provide relevant shielding when placed on a series of hollow trapezium-like cores of sufficient height. KEYWORDSSound propagation, building skin, building envelope greening, green roofs, sustainable buildings, quiet side 1.INTRODUCTIONStreet surfaces and building facades most often consist of acoustically rigid materials like glass, concrete, tiles, bricks, pavements, and so on. As a consequence, there is often a strong increase in sound pressure level due to the multiple reflections in between opposing building facades and on the street surface. Heutschi 1 proposed a simplified model for the so-called "building correction" for typical street geometries based on a ray-tracing numerical model. Parameters that were identified as relevant were the height of the facades, width of the street (canyon), the absorption coefficient of the facades, the degree of diffusion and source/receiver positioning. Thomas et al. 2 proposed the "reflection ratio", an impulse response based indicator, which was measured in 99 real streets in a city centre. The main influencing parameters were street width, facade height and facade roughness. The large number of reflections inside the street clearly affect the sound intensity incident on the directly exposed facade of a building. Although increasing the acoustic insulation of a facade might be helpful to mitigate noise issues, window opening habits might strongly deteriorate the overall facade insulation and consequently increases the noise levels to which dwellers are exposed indoors 3,4 . Although one might opt for windows that cannot be opened or try to minimize their surfaces, such choices can conflict with preferences and a lower overall perceived comfort. There is a bulk of research [5][6][7][8][9] showing that there are various ways to reduce this street amplification. There are two major directions to follow namely increasing the diffusivity of the facades or increasing the absorption rate of the materials used (in a fixed geometry), similar to what is commonly done in room acoustic design.

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“…From the acoustic perspective, the insulation capability of the vegetated roof is generally recognized to be a function of the growing substrate thickness and density [23], while the acoustic absorption coefficient is mostly affected by the organic content, and by the ground compaction level [22]. Additionally, both properties seem to be somehow influenced by the water content in the substrate itself [30].…”

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confidence: 99%

Thermo-acoustic performance of green roof substrates in dynamic hygrothermal conditions

Fabiani¹,

Coma

Pisello

et al. 2018

Energy and Buildings

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Green roofs can be considered as effective and esthetically appreciated passive tools for energy saving systems in buildings. In particular, the effect of evapotranspiration and the large thermal inertia of such solutions, represent highly attractive properties to be implemented in advanced building envelope components. Although these properties are deeply influenced by external factors such as weather conditions, and greenery dynamics, the materials used in substrate and drainage layers are too commonly assumed as constant thermal insulation layers depending only on their physical properties and water content. In particular, common disaggregated materials used in internal layers of extensive green roofs, generally are characterized by a highly complex matrix, and consequently, such materials usually lack of realistic thermal-acoustic properties evaluation. The main objective of the study is to investigate the impact of water content on the thermo-acoustic performance of different disaggregated materials from green roofs substrates commonly used in Mediterranean climates. In particular, the TPS method was used to assess the effect of humidification and raining processes on the final performance of the considered samples. An extensive acoustic characterization was also developed, based on the acoustic transfer function method. Results show that raining processes can highly influence the thermal performance of such materials, which depending on their density, can even triple their thermal conductivity value and achieve twice the volumetric specific heat at ambient conditions. Furthermore, the acoustic characterization procedure showed that the biggest modification on the final acoustic absorption and insulation capability, i.e. about 20 dB when the 80 mm samples, was produced by increasing the water content of the system from 10% to 30% RH. On the contrary, the conditioning at 90% RH does not produce significant differences of the final acoustic behavior of the substrates.

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Influence of rainfall on the noise shielding by a green roof

Cited by 17 publications

References 29 publications

Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes

Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes

Improving the noise reduction by green roofs due to solar panels and substrate shaping

Thermo-acoustic performance of green roof substrates in dynamic hygrothermal conditions

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