Green Roofs - GreenSpec

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Many airborne pollutants, including nitrates and volatile organic chemicals, may be absorbedthrough the leaf stomata and subsequently metabolised by plants (Wolverton et al 1985,Wolverton & Wolverton 1993).A major component of photochemical smog is ozone, which is formed when nitrous oxides(NO x ) and volatile organic compounds (VOCs) react on hot sunny days. High temperatures,which may be increased by the heat island effect, exacerbate the problem. Traditional darkcoloured roofs absorb sunlight and re-radiate heat contributing towards urban heat islands(see discussion on urban climate below). Stratospheric ozone filters out dangerous ultravioletradiation, but near the ground ozone is toxic – it can aggravate breathing difficulties inhumans and damage plants even in low concentrations (
Table 1 Albedo of roofs and vegetation(after Littlefair et al. 2000)Surface Albedo 1<strong>Roofs</strong>Smooth asphalt (weathered) 0.07Asphalt 0.10 – 0.15Tar & Gravel 0.08 – 0.18Tile 0.10 – 0.35Slate 0.10Corrugated iron 0.10 – 0.16Highly Reflective roof after weathering 0.60 – 0.70VegetationDeciduous plants 0.20 – 0.30Dry grass 0.30Deciduous woodland 0.15 – 0.20Coniferous woodland 0.10 – 0.15In summer, air conditioners transfer hot air into the streets. A federal programme in theUnited States encourages building owners to tackle this problem by making roofs morereflective through the application of white pigments or by using vegetation. Vegetationshades buildings and has a higher albedo than most building materials and in additionprovides cooling through evapo-transpiration. Studies by Sacramento and Phoenix haveindicated that increasing tree cover by 25% can reduce afternoon air temperatures by between6 – 10˚C, and simulations of a 30% vegetation cover produced a midday ‘oasis’ effect,reducing temperatures by as much as 6˚C (Taha 1988). Gao (1993) has shown that vegetationin streets can reduce temperatures by 2˚C.Transpiration adds humidity to what is frequently uncomfortably dry city air. Vegetated roofsmay also cause a reduction in local wind velocities by increasing the surface roughness ofbuildings.1 The albedo is the ratio of radiation refl ected from a surface to the incoming radiation onto the surface.21
Page 3 and 4: English Nature Research ReportsNumb
Page 5: SummaryThis report assesses the pot
Page 8 and 9: 6.5 Growing medium ................
Page 10 and 11: existing green roof practice and fo
Page 12 and 13: 1995). These classifications may no
Page 14 and 15: 2.4 BenefitsThe various benefits of
Page 16 and 17: potential contribution the construc
Page 18 and 19: have been published which can be di
Page 22 and 23: Figure 2 Vegetation shades the buil
Page 24 and 25: 4.6 NoiseIt has been estimated that
Page 26 and 27: porridge, beer, yoghurt or rice wat
Page 28 and 29: The turfed area supported a dense t
Page 30 and 31: Mallin (1980) reported frequent use
Page 32 and 33: Action Plan. Its natural habitat is
Page 34 and 35: 6. Design and constructionBrownlie
Page 36 and 37: y dedicated mats or multipurpose la
Page 38 and 39: Figure 5 Filter fleece prevents sil
Page 41: studies of patterns of colonisation
Page 45 and 46: FORMAN, R.T.T., 1991. Landscape cor
Page 47 and 48: SAEFL, 1998. Swiss landscape concep
Page 49: 9. AcknowledgementsThanks to John N
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Page 60 and 61: Websitewww.sfg-gruen.chwww.sierracl

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