The design and installation of green roofs requires an understanding of numerous aspects within a project. Here, Richard Clews of Prater looks into the factors contributing to the expansion of the market and the key areas that need to be considered when implementing a green roof system.
The green roof market has increasingly become a part of modern building design. According to a recent report published by Livingroofs.com, the market has actually seen a 17% year on year increase.
Policies such as the mayor’s London Infrastructure Plan 2050, which targets big businesses through the capital business improvement districts (BIDs), are helping to focus future builds around their environmental impact. The action has already led to the installation of fruit and vegetable gardens on top of notable London offices. Audits of London’s BIDs have also identified further scope to create 100 hectares of green roofs.
With space for development at a premium and the introduction of policies such as the London Infrastructure Plan, green roofs are frequently a condition within planning permissions on certain types of projects or in specific areas. However, while London currently installs around 42% of all UK green roofs, focus now has to shift away from London, with future growth dependent on local initiatives and further government action.
Maximise the benefits
For architects looking to maximise the available space in either a residential or commercial urban environment, a green roof can often be the ideal solution. Green roof systems deliver added value to a project and can help developers to amplify the return on investment.
Green urban spaces have the potential to help architects attain sustainability criteria’s such as BREEAM and LEED, as well as support an organisation’s corporate social responsibility goals.
Green roof systems can also play an important role in managing rainfall in urban areas to aid prevention of flooding. Unlike materials such as concrete and metal, the trees, plants and soil that make up a green roof will absorb water following heavy rainfall and discharge it more slowly, helping to avoid flash flooding.
Due to the nature of green roofs as a living material, there are specific considerations that need to be addressed.
Careful planning is required before installation begins to ensure that the materials can be delivered to site exactly when needed. In particular, sedum green roofing ideally needs to be fitted within 24 hours of delivery to prevent damage to the vegetation.
Green roof systems can also present particular challenges when it comes to installation. These areas are often large and the volume of substrate material that needs to be installed means that the process needs to be planned and coordinated before work on site can begin. The insulation and waterproofing also needs to be suitable for the application. A robust system that meets the requirements for the whole building, including the living components will help avoid costly remedial work and ensure longevity.
Finally, long-term and regular maintenance of the green roof should also be factored in. While extensive green roofs are generally robust and considered low maintenance this still needs to be a consideration.
When Prater began work on the roofing package for the Peacehaven waste water treatment plant near Brighton, a number of factors had to be considered to deliver what was, at that point, the largest green roof of its type in the UK.
Prater worked closely with main contractor 4Delivery and architect Montgomery Watson Harza to develop the design, which included a 16,050 m², fully turfed landscape rather than the more standard sedum green roof. In order to gain planning permission, it was crucial for the project team to demonstrate that the facility would complement the surrounding countryside. To help achieve this, the seed mix was carefully selected to change with the seasons in the same way the immediate landscape would and the turf was cultivated offsite for 15 months to ensure a mature green roof could be established immediately.
Furthermore, the volume of material required presented a logistical challenge on site and required careful planning. Transferring thousands of tonnes of substrate onto the metal deck roof was achieved using mobile tower cranes and a series of conveyor belts. The material was then raked to follow the curve of the building and the turf applied.
The NFRC Roofing Award winning, Fitzroy Place development in London required green roofing across numerous buildings. However work on commercial and residential projects was being carried out at the same time within a confined site area. The Prater team had to ensure project delivery times were adhered to and materials were brought to site precisely when needed in order to keep site congestion to a minimum.
Part of the Fitzroy development required a green roof on the Grade II listed Fitzrovia Chapel. Therefore it was important to select insulation and waterproofing that was suitable for green roof application but would also protect the integrity of the chapel’s roof.
Prater undertook all of the design detailing for the inverted roof application to ensure the development of an appropriate and efficient design solution. The team also worked closely with supplier, Radmat, to verify all designs and establish high specifications for insulation and waterproofing materials.
Specifying and installing a green roof can, in some cases, be extremely complicated. Therefore it is always advisable to involve a specialist roofing contractor early within the design process to provide guidance and technical expertise. This early contact can help ensure that designs are in line with the aesthetics, technical performance, sustainability and ecological needs the client and end user requires.
Richard Clews is pre contracts manager at Prater