EFB — Extensive and Intensive Green Roofs

EFB - Extensive and Intensive Green Roofs

Extensive and Intensive Green Roofs

(by livingroofs.org)


Green Roofs are, in short, vegetated roofs, or roofs with vegetated spaces. They are also referred to as eco-roofs and roof gardens. Green roofs have been with us for centuries ranging from the hanging gardens of Babylon to the turf roofed dwellings of Ireland and Scandinavia. However, modern green roofs have largely developed in the last 50 years, with increasing sophistication to meet a growing range of needs.

Most of this technological advance has been made in Germany; their growth in the 1970s and 1980s has lead to £39million industry. The modern green roof systems are highly durable and provide a number of key sustainable and environmental benefits. The German Green Roof Standards, known as the FLL, are very high and all systems are required to be tested for to ensure that they perform to the highest building standards, whether that be waterproofing or fire resistance. No such standards are in force within the UK, although the larger manufacturers accord to them.

Within the UK the growth of self-build and ecological construction processes from the late 1960s saw an increasing interest in green roofs over the following decades. However, this was never fully exploited by either the industry or policy-makers, and consequently the UK remains without incentives, standards, or policies to encourage the installation of green roofs.

Myths still abound. In the UK there are concerns within the professions and public that green roofs are more liable to leak than traditional roofing systems. This is partly down to a preference for pitched, rather than flat roofs. However, vegetated roofs provide an extra protection to waterproofing systems from Ultra-Violet light, frost, erosion and other forms of weathering. If in the rare case that they do leak, this is largely down to poor roof construction, and not the green roof system itself.

Nevertheless, within the past 5 years we have witnessed a significant renewed interest in green roofs, and a marked increase in green roofs being designed and installed. Many of these are part of urban regeneration schemes, but be it the garden shed or a large commercial block in the heart of our cities, the opportunities are almost endless. We are, we believe, on the crest of a third wave of green roofs in the UK. Mechanisms are now being put in place to help ensure that this interest is sufficiently captured and developed in a way that the necessary policies, incentives and regulatory frameworks in put in place.

This requires research pertinent to the UK, policy development, and advocacy to all levels of Government, which Livingroofs.org is setting out to achieve.

Livingroofs.org aims to promote green roofs, green walls and other similar features, at all levels, working with industry, contractors, local authorities regeneration teams, researchers, and the wider public to ensure that they become a mainstream component of building design and function.

Extensive Green Roofs

Extensive green roofs have a thin growing medium and require minimal maintenance, and in general due not require irrigation [some require irrigation initially]. They are generally less costly to install than intensive green roofs.

There are 3 types currently used in the UK:

1. Sedum mats

Sedum Mats — a sedum mat is a base layer of Polyester, Hessian, or porous polythene depending on the supplier, on which is laid the 2cm growing medium, on to which is sprinkled sedum cuttings. These grow into the substrate to maturity. When harvested the Sedum blanket is rolled up from the carrier upwards and delivered to site. When installed the Sedum blanket (including the 2cm of growing medium) is rolled out onto either 5 — 7cm of growing medium (standard method) or direct onto a moisture retention blanket (ultra light weight method).

Sedums are used because they are wind, frost and drought resistant not because they absorb water. Its ability to absorb water makes it drought resistant.

2. Substrate based roof

7cm of crushed recycled brick is placed on the green roof system and plug planted with sedums or with sedum mats applied. There is a misconception that green roofs are made of turf. Although some green roofs are made of turf this is not generally the case.

3. Green / Brown roofs for biodiversity

Similar to substrate based but can, in some cases, use recycled aggregate from site and generally left to colonise naturally or seeded with an annual wildflower mix or local seed source.

Intensive Green Roofs

Intensive green roofs have a deep growing medium, which allows the use of trees and shrubs. Some city parks are in fact intensive green roofs, such as the parks within the Canary Wharf Estate, Canada Square and West Ferry Circus and the roof of Cannon Street Station in London The depth of the growing medium requires extra loading requirements within the holding structure and requires a complex irrigation system for maintenance. They are generally quite costly and require extra structural design to the building.

intensive green roofs require extra loading requirements

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