The demand for green roof technologies is ramping up, yet they are complex structures that require understanding; luckily a range of information sources are available to architects and specifiers. Amanda de Sousa of BMI UK & Ireland explains more
According to a report published in April by the Greater London Authority, there are over 1.5 million m2 of green roofs in London, and there is a raft of reasons why. Green roofs offer a host of environmental benefits including, reducing storm water run-off, increasing biodiversity, cooling buildings and their surroundings as well as improving water and air quality. There is also a growing body of evidence that shows how they positively contribute to wellbeing, by offering views of nature or by providing an amenity such as a roof garden.
Following the growth of green roofs comes a rise in ‘blue roofs’ – which retain water – too, often with the two types combined. As more planners demand sustainable urban drainage systems (SuDS), blue roofs offer a way to release the rainwater more slowly, avoiding the risk of over-burdening drainage systems and causing flooding.
In London, as in other cities around the world, planning policy is driving the trend for roofs that do more. In 2008, London’s mayor published a guide on living roofs and walls to complement its London Plan. By 2016, over 40 per cent of the UK’s green roofs were in the capital. In 2014, current Mayor Sadiq Khan improved on this by declaring his intention to make the capital a National Park City, with green roofs part of the urban greening plan.
Other UK towns and cities are following London’s lead. For instance, Cambridge City Council is developing a green roof policy as part of its local plan to increase sustainability. And Leicester’s green infrastructure strategy includes plans to encourage more green roofs on both new-build and refurbishment projects.
Yet green roof types, while well established, present design challenges to the specifier and it would be beneficial to up skill in this field – most accessibly through CPD training such as that provided by BMI UK & Ireland.
There are structural implications when adding a green or blue roof to a building. A blue roof, for instance, at capacity would add around 1 kN/m2 to the loading. New buildings can be designed accordingly but care must be taken with retrofits.
Though green roofs and their design are well documented, there is less guidance on the design of blue roofs, other than that published by the NFRC. However, BS 6229:2018 ‘Flat roofs with continuously supported flexible waterproof coverings – code of practice,’ published in November 2018, does make reference to blue roofs and addresses the important issue of falls.
Though blue and green roofs add extra dimensions to the uses and value of roofs, they also require an additional dimension of care with respect to design, installation and quality control.
Typical CPD content would include green specification considerations, including compatible roofing system specification, usage and structural requirements; vegetation and planting methods; maintenance and aftercare; and green roofs in practice. While in-depth, expert calculation and design input should ideally be sought from manufacturers, such CPDs provide an invaluable overview to understanding the nature, options and issues surrounding these structures.
Companies such as BMI UK & Ireland can provide specification, design and technical expertise throughout the process. They can deliver advice and quality assurance during the installation process to ensure that the delivered roof – and amenity – meets the designs module.
Amanda de Sousa is product systems manager at BMI UK & Ireland