As a green infrastructure component, green walls have the potential to deliver many ecosystem services. They have experienced a revived interest since the creation of the Living Wall Systems approximately 20-25 years and are now quite familiar in urban areas.
Green walls, as with any other green infrastructure, create a semi-natural habitat when used in an urban environment. Irrespective of their size, structure or vegetation composition, they provide visual amenity. When free-standing, by structuring open areas they provide intimacy. Against a wall, they have the ability to hide ugly features or prevent damage such as graffiti.
Along with other infrastructure, Green Walls have the potential to address the following issues:
Microclimate Mitigation and Urban Heat Island reduction
Several studies have proved the potential of green walls to mitigate the weather through passive heat island reduction and thermal regulation of buildings. The mitigation is due to four mechanisms: (i) the ability of plants to intercept solar radiation through their shading, (ii) the effect of evapotranspiration by plants that can extract heat from the surrounding air, (iii) the thermal insulation provided by the vegetation (and by the substrate and structure in the case of living wall systems) and by the air gap between the vegetated structure and the building, and (iv) the alteration of the wind effect on the building.
The ability of plants to improve a building’s microclimate has been well investigated, focusing at first on green façades and hedges, and, more recently, on living wall systems. In the 1980’s, one of the first studies looked at the use of wisteria, vine and ivy as solar control and established the inverse correlation between solar transmittance and ivy growth conditions; thus highlighting the potential use of green walls for thermal insulation.
Urban hedges and green screens, through their freestanding status, were studied for their thermal mitigation effect on the microclimate of the street canyon. As other green walls, they have significant functions of shading, lowering temperature, increasing humidity and modifying wind. Their efficiency will depend on the type of plant species and on the rooting media; e.g. mulch, acting as insulation, re-radiates more energy than other media like turf. Hedge presence (shrub cover or tree and shrub cover) was shown to reduce temperature in a built environment by at least 1°c, comparable to the modification of ambient temperature by living walls and green façades (from 1 to 4°c,), thus reducing the urban heat islands (UHIs).
Due to the complexity of thermo-dynamic transmission process, studies usually focused on the development of computer models exploring the effect of a vertical greening system on a building and in a street canyon. They showed that the best efficiency of green walls for thermal mitigation will depend on locality, climatic elements and wall aspect but that the leaf density (expressed by the Leaf Area Index), which affects the amount of shade produced, and the evapotranspiration from the plantation are also important.
Experimental and simulation studies were mainly done in the Mediterranean area or in tropical climates; the main aim was usually to establish how green walls could assist in cooling building in summer rather than reducing heat loss in winter. Thus, green walls were showed to provide a significant cooling effect on the building surface, reducing the peak temperatures in summer. But in addition to the shading that reduces solar gains to the building and reduces heat flow into the building through passive cooling, green walls were also shown to be able to decrease heat flow losses and hence improve the energy efficiency of buildings.
Noise annoyance, especially along road corridors, is a major issue in urbanized areas and noise barriers have become ubiquitous features along busy roads. Their efficiency and integration into their surrounding appears to be enhanced by the presence of vegetation, as plants (especially leaves and stems) scatter high frequency sound waves, which have been shown to have a significant effect on human health.
Along with green roofs, green walls have been investigated for their acoustic effect, although to a smaller extent. Urban hedges were shown to have a significant effect in lowering noise, especially when composed of both shrubs and trees due to the multi-layered structure.
Air quality improvement
In urban areas, green walls, as well as other vegetated elements, have been investigated for their potential role in reducing air pollution, through particulate filtering. The dust-filtering ability of a plant is directly correlated with the foliar surface characteristics, the size, the hair density on the leaves and the quantity of lead waxes. With a large collecting surface area, green walls can play a great role in improving air pollution, especially as they promote vertical transport by enhancing turbulence. By assessing particulate abatement capacity (PAC), it has been found that hedgerows can provide an efficient barrier against road dust and can reduce particulate matter by 30% to 40%. Hedges can remove concentrations of total suspended particulate (TSP) and PM10 by up to 40-50%. The efficiency of vegetation to mitigate particulate pollution appears to depend on the density of planting, the plant canopy density, porosity and size, and the leaf morphology. As such, shrubs and hedges appear to be more efficient than trees (especially conifers) for dust-retention.
In addition to the particulate size, the chemical composition of the trapped particulates is of interest, especially in terms of heavy metals, as it has significant effect on human health. Having a green façade is an easy way to improve air quality as climbers like Parthenocissus tricuspidata (Japanese Creeper) are passive accumulators of heavy metal aerosol pollutants.
Green roofs have been extensively studied for their ability to manage urban stormwater. Following the trend, similar studies have been made on green walls.
Green walls have the potential to contribute to the improvement of urban animal biodiversity by creating habitat, food sources (e.g. for wintering birds), corridors, nesting sites, etc. However, little work has been done on this topic. Previous work published in German (see Köhler, Barth, Brandwein, & Gast, 1993 and reference therein), showed that green façades (either with ivy or grapevines) can be colonized by 19 different taxa of invertebrates from Araneae and Diptera to Diplopoda and Siphonaptera. Although important work has been done on the animal biodiversity of green façades in Germany and of green roofs (Grant & Lane, 2006; Kadas, 2011; Madre, Vergnes, Machon, & Clergeau, 2013), findings are either difficult to access for non-German speakers, or not transferable to green walls. Recently,a 2-year study on green façades showed the value of green walls for urban birds. More birds were recorded directly on the walls or in their close surroundings, than in the exact same environment without vegetation on the wall (Chiquet, Dover, & Mitchell, 2013). Another work has studied the snail populations of green façades, showing the influence of seasonality and foliage on the relative abundance of species (Chiquet, Dover, & Mitchell, n.d.).
Anderson, L., Mulligan, B., & Goodman, L. (1984). Effects of vegetation on human response to sound. Journal of Arboriculture, 10(February), 45–49.
Aylor, D. E. (1971). How plants and soil muffle noise. Frontiers of Plant Science, 6–7.
Baldauf, R., Thoma, E., Khlystov, A., Isakov, V., Bowker, G., Long, T., & Snow, R. (2008). Impacts of noise barriers on near-road air quality. Atmospheric Environment, 42(32), 7502–7507. doi:10.1016/j.atmosenv.2008.05.051
Baudry, J., Bunce, R. G. H., & Burel, F. (2000). Hedgerows: An international perspective on their origin, function and management. Journal of Environmental Management, 60(1), 7–22. doi:10.1006/jema.2000.0358
Berrien, F. K. (1946). The effect of noise. Psychological Bulletin, 43(2), 141–161.
Brunekreef, B., & Holgate, S. T. (2002). Air pollution and health. Lancet, 360(9341), 1233–42. doi:10.1016/S0140-6736(02)11274-8
Calhoun, J. B. (1962). Population density and social pathology. Scientific American, 206(2), 139–150.
Calhoun, J. B. (1971). Space and the strategy of life. In A. H. Esser (Ed.), Behavior and Environment (pp. 329–387). Springer US.
Chen, F., Zhou, Z., Guo, E., & Ye, Z. (2006). Dust-retention effect of ornamental green land in urban industrial area: A case study in Wuhan Iron and Steel Company workshop area. Shengtaixue Zazhi, 25(1), 34–38.
Chen, Q., Li, B., & Liu, X. (2013). An Experimental Evaluation of the Living Wall System in Hot and Humid Climate. Energy and Buildings, 61, 298–307. doi:10.1016/j.enbuild.2013.02.030
Cheng, C., Cheung, K., & Chu, L. (2010). Thermal performance of a vegetated cladding system on facade walls. Building and Environment, 45, 1779–1787.
Chiquet, C., Dover, J. W., & Mitchell, P. (n.d.). The abundance of snail (mollusca: gasteropoda) on urban green walls and the influence of sampling methods. submitted.
Chiquet, C., Dover, J. W., & Mitchell, P. (2013). Birds and the urban environment: the value of green walls. Urban Ecosystems, 16, 452–462.
Den Boer, L., & Schroten, A. (2007). Traffic noise reduction in Europe. CE Delft (p. 70). CE Delft.
Dinsdale, S., Pearen, B., & Wilson, C. (2006). Feasibility study for green roof application on Queen’s University campus. Queen’s Physical Plant Services.
Dover, J. W. (2006). Embedding Green Infrastructure in Housing Market Renewal. Biodiversity and Green Infrastructure Document Review v.1.1. Funders RENEW North Staffordshire, Natural England, Sustainability West Midlands. Unpublished project report. (p. 82).
Dunnett, N., & Kingsbury, N. (2004). Planting green roofs and living walls. Landscape Architecture (2, revised., Vol. 129, p. 328). the University of California: Timber Press, 2008.
Eumorfopoulou, E. a., & Kontoleon, K. J. J. (2009). Experimental approach to the contribution of plant-covered walls to the thermal behaviour of building envelopes. Building and Environment, 44(5), 1024–1038. doi:10.1016/j.buildenv.2008.07.004
Francis, R., & Lorimer, J. (2011). Urban reconciliation ecology: the potential of living roofs and walls. Journal of Environmental Management, 92(6), 1429–1437. doi:10.1016/j.jenvman.2011.01.012
Freedman, J. (1975). Crowding and behavior (p. 177). W.H.Freeman & Co Ltd.
Giridharan, R., Lau, S. S. Y., Ganesan, S., & Givoni, B. (2008). Lowering the outdoor temperature in high-rise high-density residential developments of coastal Hong Kong: The vegetation influence. Building and Environment, 43(10), 1583–1595. doi:10.1016/j.buildenv.2007.10.003
Gobel, P., Dierkes, C., Kories, H., Messer, J., Meissner, E., & Coldewey, W. G. (2007). Impacts of green roofs and rain water use on the water balance and groundwater levels in urban areas. Grundwasser, 12, 189–200. doi:10.1007/s00767-007-0032-y
Grant, G., & Lane, C. (2006). Extensive green roofs in London. Urban Habitats, 4(1), 51–65.
Holm, D. (1989). Thermal improvement by means of leaf cover on external walls - a simulation-model. Energy and Buildings, 14(1), 19–30.
Hoyano, A. (1988). Climatological uses of plants for solar control and the effects on the thermal environment of a building. Energy and Buildings, 11(1), 181–199.
Jaffe, M., Zellner, M., Minor, E. et al. (2010). Using green infrastructure to manage urban stormwater quality: a review of selected practices and state programs. A Report to the Illinois Environmental Protection Agency.
Jim, C., & He, H. (2011). Estimating heat flux transmission of vertical greenery ecosystem. Ecological Engineering, 37(8), 1112–1122. doi:10.1016/j.ecoleng.2011.02.005
Johnston, J., & Newton, J. (2004). Building Green. A guide to using plants on roofs,walls and pavements (p. 121). London: Greater London Authority.
Kadas, G. (2011). Green Roofs and Biodiversity: Can Green Roofs Provide Habitat for Invertebrates in an Urban Environment? (p. 302). Lambert Academic Publishing.
Kittas, C. (1992). Influence d’un brise-vent sur les pertes convectives et radiatives d'une serre. Boundary-Layer Meteorology, 61, 99–111.
Köhler, M. (2007). Rain Water Management with Green Roofs and Living Walls. In II International Water Conference 12-14 September 2007 (p. 13). Berlin.
Köhler, M. (2008). Green facades—a view back and some visions. Urban Ecosystems, 11(4), 423–436. doi::10.1007/s11252-008-0063-x
Köhler, M., Barth, G., Brandwein, T., & Gast, D. (1993). Fassaden-und Dachbegrünung. Ulmer Fachbuch.
Kontoleon, K. J. J., & Eumorfopoulou, E. (2010). The effect of the orientation and proportion of a plant-covered wall layer on the thermal performance of a building zone. Building and Environment, 45(5), 1287–1303. doi:10.1016/j.buildenv.2009.11.013
Kotzen, B. (2004). Plants and environmental noise barriers. In: Junge-Berberovic, R., Baechtiger, J.-B. and Simpson, W.J., (eds.) Proceedings of the International Conference on Urban Horticulture. Acta Horticulturae (643). International Society for Horticultural Science, Leuven, Belgium, pp. 265-276.
Kruuse af Verchou, A. (2005). Green roofs, storm water management, and biodiversity in Malmo, Sweden. Ecosystems and Sustainable DevelopmentV, 81, 171–179.
Kulshreshtha, K., Rai, A., Mohanty, C. S., Roy, R. K., & Sharma, S. C. (2009). Particulate pollution mitigating ability of some plant species. International Journal of Environmental Research, 3(1), 137–142.
Larcher, F., Merlo, F., & Devecchi, M. (2013). The use of Mediterranean shrubs in Green Living Walls. Agronomic evaluation of Myrtus communis L. In: ISHS Acta Horticulturae 990 II International Symposium on Woody Ornamentals of the Temperate Zone, pp. 495–500.
Lin, Y., Wu, X., Hao, X., & Han, C. (2011). Influence of green belt structure on the dispersion of particle pollutants in street canyons. Acta Ecologica Sinica, 31(21), 6561–6567. doi:1000-0933(2011)31:21<6561:csjdcd>2.0.tx;2-a
Loh, S. (2008). Living walls - a way to green the built environment. BEDP Environment Design Guide, (August), 1–7.
Lundholm, J., & Peck, S. (2008). Introduction: Frontiers of green roof ecology. Urban Ecosystems, 11(4), 335–337. doi::10.1007/s11252-008-0070-y
Madre, F., Vergnes, A., Machon, N., & Clergeau, P. (2013). A comparison of 3 types of green roof as habitats for arthropods. Ecological Engineering, 57, 109–117. doi:10.1016/j.ecoleng.2013.04.029
Mazzali, U., Peron, F., & Romagnoni, P. (2013). Experimental investigation on the energy performance of living walls in temperate climate. Building and Environment, 64, 57–66. doi:10.1016/j.buildenv.2013.03.005
McPherson, E., Scott, K., & Simpson, J. (1998). Estimating cost effectiveness of residential yard trees for improving air quality in Sacramento, California, using existing models. Atmospheric Environment, 32(I).
Montague, T., Kjelgren, R., & Rupp, L. (1998). Surface energy balance affects gas exchange of three shrub species. Journal of Arboriculture, 24, 254–262.
Ning, Z., Min, L., & Yizin, C. (2002). Ecological functions of green land system in Harbin. Yingyong Shengtai Xuebao, 13(9), 1117–1120.
Ochoa, J. M. (1999). Vegetation as an instrument for climate control. Doctoral Thesis. Technical University of Catalonia,School of Architecture.
Okinaka, T., Nojima, Y., Kobayhi, T., & Seto, H. (1994). Covering effects of climbing plants on wall temperature of concrete building. Technical Bulletin of Faculty of Horticulture Chiba University, 48, 125–134.
Ottelé, M. (2011). The Green Building Envelope. Vertical Greening. Doctoral Thesis. Department of Materials and Environment, Technical University Delft, Delft.
Pal, A. K., Kumar, V., & Saxena, N. C. (2000). Noise attenuation by green belts. Journal of Sound and Vibration, 234(1), 149–165. doi:10.1006/jsvi.2000.2863
Paulus, P. B., Cox, V.C. & McCain, G. (1988). Prison crowding: A psychological perspective. Research in Criminology. (p. 115). Springer-Verlag.
Pérez, G., Rincón, L., & Vila, A. (2011). Behaviour of green facades in Mediterranean Continental climate. Energy Conversion and Management, 52(4), 1861–1867. doi:10.1016/j.enconman.2010.11.008
Perini, K., Ottelé, M., Haas, E. M. E. M., Raiteri, R., & Ottele, M. (2013). Vertical greening systems, a process tree for green façades and living walls. Urban Ecosystems, 16(2), 265–277. doi:10.1007/s11252-012-0262-3
Roehr, D., & Laurenz, J. (2008). Living skins: environmental benefits of green envelopes in the city context. In: Broadbent, G. and Brebbia, C.A. (eds.) Eco-Architecture II: Harmonisation between Architecture and Nature, 149–158.
Rutgers, R. (2012). Living Façades: A study on the sustainable features of vegetated façade cladding. Faculty of Architecture. Delft University of Technology, Delft.
Schmidt, M. (2006). Evapotranspiration cooling of greened roofs and façades. Greening Rooftops for Sustainable Communities.Proceedings of the Boston Conference. Green Roofs for Healthy City. Toronto.
Shan, Y., Jingping, C., Liping, C., & Zhemin, S. (2007). Effects of vegetation status in urban green spaces on particle removal in a street canyon atmosphere. Acta Ecologica Sinica, 27(11), 4590–4595.
Simmons, M., Gardiner, B., Windhager, S., & Tinsley, J. (2008). Green roofs are not created equal: the hydrologic and thermal performance of six different extensive green roofs and reflective and non-reflective roofs in a sub-tropical climate. Urban Ecosystems, 11(4), 339–348. doi::10.1007/s11252-008-0069-4
Spolek, G. (2008). Performance monitoring of three ecoroofs in Portland, Oregon. Urban Ecosystems, 11(4), 349–359. doi::10.1007/s11252-008-0061-z
Stec, W., Paassen, A. Van, & Maziarz, A. (2005). Modelling the double skin facade with plants. Energy and Buildings, 37(5), 419–427. doi:10.1016/j.enbuild.2004.08.008
Susorova, I., Angulo, M., Bahrami, P., & Stephens, B. (2013). A model of vegetated exterior facades for evaluation of wall thermal performance. Building and Environment, 67, 1–13. doi:10.1016/j.buildenv.2013.04.027
Thönnessen, M., & Werner, W. (1996). Die fassadenbegrünende Dreispitzige Jungfernrebe als Akkumulationsindikator. Gefahrstoffe Reinhaltung Der Luft, 56, 351–357.
Van Renterghem, T., & Botteldooren, D. (2009). Reducing the acoustical facade load from road traffic with green roofs. Building and Environment, 44(5), 1081–1087. doi:10.1016/j.buildenv.2008.07.013
Varshney, C. K., & Mitra, I. (1993). Importance of hedges in improving urban air-quality. Landscape and Urban Planning, 25(1-2), 75–83.
Weinmaster, M. (2009). Are green walls as “green” as they look? An introduction to the various technologies and ecological benefits of green walls. Journal of Green Building, 4(4), 3–18.
Wong, N. C. N. H., Tan, A. Y. K., Chen, Y., Sekar, K., Tan, P. Y., Chan, D., & Chiang, K. (2010). Thermal evaluation of vertical greenery systems for building walls. Building and Environment, 45(3), 663–672. doi:10.1016/j.buildenv.2009.08.005
Wong, N., Tan, A. Y. K., & Tan, P. Y. (2009). Energy simulation of vertical greenery systems. Energy and Buildings, 41(12), 1401–1408. doi:10.1016/j.enbuild.2009.08.010
Yang, H. S., Kang, J., & Choi, M. S. (2012). Acoustic effects of green roof systems on a low-profiled structure at street level. Building and Environment, 50(0), 44–55. doi:10.1016/j.buildenv.2011.10.004
Yaomin, Q., Kang, L., & Yongjun, W. (2006). Ecological functions of green land system in Xi’an. Shengtaixue Zazhi, 25(2), 135–139.
Zaiyi, M., & Niu, J. (1998). Study on thermal function of ivy-covered walls. Conference Proceedings, Building Simulation, 1–8. International Building Performance Simulation Association.
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