types of green roof
Recreation Roofs
Recreation Roofs are designed specifically for recreation, although the inclusion of vegetation in planters (such as on terraces or balconies) is often used to enhance their visual attractiveness. Recreation roofs are those that have no substrate and no intentionally vegetated part to their construction. Because of this they have limited SUDS (sustainable urban drainage systems) or climate change adaptation benefit, (except cool roofs – see below) and no biodiversity value.
Recreation roofs, where there is adequate space available, are well suited for sports such as ball games.
Examples of recreation roofs in London can be found at
Hanover school Islington and at Springbok Works, Hackney.
These living roof types, and all the other variants in between, can bring a variety of environmental benefits including climate change adaptation, enhanced building energy balance, Urban Heat Island Effect, biodiversity, sustainable drainage, and amenity. These are illustrated in Figure 1 above and Table 1 page 15.
Cool Roofs
One further roof type that it is useful to define is the cool roof, although these are not considered in any detail beyond this point. Cool roofs are a form of roof where the materials used are deliberately selected for their high solar reflectance (albedo) and high thermal emittance. They absorb, and consequently store, less solar energy during the day and thus are not major emitters of heat into the urban atmosphere at night. Cool roofs reach temperatures considerably lower than their low reflectance counterparts. They can extend the lifetime
of roof materials by damping the daily temperature range and thus reducing excessive contraction and expansion, and by reducing the absorption of damaging ultraviolet. To ensure the effectiveness of cool roofs their reflectivity must be maintained as it declines with age, and they need to be kept clean as dirt and pollution lower reflectivity.
Living Walls
Living walls are those covered in some form of vegetation. Generally they are comprised of climbing plants of one kind or another, and are designed so as to support such vegetation. More radically, living walls are now being constructed that provide an additional structure into which vegetation can actually be planted. Depending on the species used living walls can provide environmental benefit in the form of biodiversity, thermal insulation and cooling benefit to the building, and noise attenuation.a number of recent case studies including examples at: Springbok Works, Dalston; New Providence Wharf, Docklands; Bishops Square, Spitalfields; Jubilee Gardens, Canary Wharf; Clearwater Yard, Camden; Ethelred Estate, Lambeth; Laban Dance Centre, Deptford and One SE8, Deals Gateway also in Deptford. [Ref: 3.2] (See also Appendix 2 Case Study Matrix).
Existing and new developments offer an opportunity
to dramatically increase the amount of living roof
and wall space throughout London and by so doing deliver substantial social and environmental benefits. Clearly, there is an interest and a commitment to include living roofs in new development as the case studies included in this report detail. With additional policy support the number of installations and retrofits, and
the necessary skills to provide them, are bound to increase significantly.
The environmental and economic benefit to London of living roofs and walls is hard to ignore. Consider the potential impact on the city’s energy budget: the GLA estimate that buildings cover 24,000 hectares or 16
per cent of Greater London [Ref: 3.3]. Crude calculations of the potential for green roofs in four areas of central London (see section 2.7) suggest that a surface area of 10 million m2, 3.2 million m2 had the potential to be greened. This would give a potential energy saving of 19,200 MWh per year or the equivalent of 8,256 CO2 e tonnes, and a capacity to store in the region of 80,000m3 of rainwater at roof level, the equivalent to, approximately, the volume of water needed for 35 Olympic swimming pools.
Accessible roof space can provide much needed amenity and visual quality as part of the increasingly dense urban form of London. By supporting a more compact city, living roofs can support the use of less land, a smaller building envelope, lower volume of materials, reduced energy consumption and lower construction costs. They can also help reduce energy requirements. For example in H.R.Presig et al., Okolgische Baukompetenz, Zurich 1999, research demonstrated that a block of eight flats consumed 68 per cent of the energy consumed by eight separate and dispersed houses of comparable volume.
There are many variables that could change these figures one-way or another but there is no doubt that the contribution of living roofs (to say nothing of the contribution of living walls or even a combined approach) in this respect wo
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