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GREEN ROOF

 Introduction




Living roofs and walls can enhance biodiversity, reduce the risk of flooding (by absorbing rainfall), improve a building’s thermal performance, thus reducing associated energy costs, help counter the Urban Heat Island Effect, support higher density more sustainable development and improve the appearance of the city.
However, despite these potential benefits, take up in London has been a lot slower than in other European and American cities.
A lack of positive policy support, concerns over development costs and a lack of technical standards have all been cited as possible reasons.
As part of the requirement to keep the London Plan up to date, the Mayor has reviewed the strategy of the plan and concluded that its direction holds. However, commitments were made to give more emphasis to the issue of climate change including sustainable design
and construction and carbon dioxide emissions.
The Mayor’s Chief Advisor on Architecture and Urbanism, Richard Rogers, has stated that a requirement for living roofs to be part of all major development would deliver a step change in the battle against climate change and the delivery of a more liveable city. It is understood from other cities that many of the obstacles to living roofs are overcome when new policy drives demand and the subsequent growth of new markets. Furthermore, there are a limited number of existing referable schemes that are already providing living roofs; it is important to reinforce and systematise this trend with thorough planning policy and preferred standards.
This report clarifies the various types of living roofs
and the environmental and social advantages each type can deliver. It goes on to address the specific benefits
of living roofs and some of the perceived barriers to
their take up.
The development of a more positive policy framework for living roofs and walls will enable London to balance its forecast growth in population and development with the environmental challenges ahead, in order to deliver a compact, resilient and liveable city that sets a new agenda for cities worldwide.

Living roofs is a broad term defined by the GLA and design for London to include green roofs, roof terraces and roof gardens. It includes roofs and structures that may be accessible by workers or residents, and that may be intensively or extensively vegetated. None of these terms are mutually exclusive, although particular types of roof treatment may be more appropriate for certain kinds of use as shown in Table 1 on page 15.
A typology has been adopted, largely based on living roof construction and use, and to reflect the benefits
to individuals and society as a whole. This typology refers to intensive and extensive green roofs, and recreation roofs.
Intensive Green Roofs
Intensive green roofs are principally designed to provide amenity and are normally accessible for recreational use. They may be referred to as roof gardens or terraces.
Generally intensive green roofs comprise a lush growth of vegetation and are based on a relatively nutrient rich and deep substrate. They allow for the establishment of large plants and conventional lawns. Intensive roofs traditionally require higher levels of maintenance, regular irrigation and applications of fertiliser. Due to the plants used, and the combined growing and drainage properties of the substrate, the weight of the intensive green roof system can be considerable. Substantial reinforcement
of an existing roof structure or inclusion of extra building structural support may be required.Extensive Green Roofs
Extensive green roofs generally provide greater biodiversity interest than intensive roofs, but are considered to be less appropriate in providing amenity and recreation benefits. In most cases they are planted with, or colonised by, mosses, succulents, wild flowers and grasses that are able to survive on the shallow
low-nutrient substrates that form their growing medium. They receive minimal management and usually no irrigation or fertilisation although it may be required initially until plants become established