Roof Garden London

During last year (2013) I did research about the implementation of green roofs in cities for my Masters at the University of Cape Town. The cases I studied and people I talked to have taught me so much. I am excited to share what I have learnt with you. The SERIOUS ABOUT GREEN ROOFS series features the core findings of my study in easy to follow parts. The theme of Part 1 is to take a closer look at the definition of a green roof as well as the policies and incentives that are used for its implementation.

Perhaps I should just start at the beginning. Change within society is encouraged through the transition of eras. Throughout time cities have responded to these era changes by moving from one type of urbanism to the next. Ultimately these types of urbanisms define the infrastructure investments launched within each era. Currently inequality and overutilization of natural resources has sparked what is called “green urbanism” under which infrastructure investments focus on the greening of developments in order to create more sustainable livelihoods. Whereas the physical infrastructure plays an important role in the transition process, it is not the only determining factor. The rules, regulations and different role players within the networks have an equal influence. Thus what is initially seen as only a physical transition now becomes a more complex process involving various social aspects as well. This is why the technology as well as its policies and incentives are important to understand.

That settles the overarching argument. Now, what exactly is a green roof? And why are green roofs and garden roofs not the same thing?  Both of these are a type of vegetative roofing system. Garden roofs usually contain plants that need more soil and maintenance, such as trees and shrubs, whereas green roofs contain plants that need less soil and maintenance, such as grass and sedums. Because of this difference other factors such as the cost, weight, and so forth are also influenced. So, why my particular interest in green roofs and not garden roofs? Because green roofs are lighter, cheaper and easier to maintain they can be installed on a wider range of buildings in a wider range of areas. Green roofs not only mitigate the effect of the Urban Heat Island and stormwater but also contribute towards biodiversity, energy efficiency, aesthetic value, improved air quality, recreational spaces as well as the potential for food production.

Green Roof

One would think that all of these benefits would, in itself, encourage the uptake of green roof projects. However, it is important to realise that not all of these benefits contribute towards the direct personal gain of the developers or building owners implementing these projects. Developers or building owners might therefore hesitate to put in the time and money to build a green roof when they only calculate the benefits that are of personal interest. It is therefore essential for policies and incentives to be put into place in order to minimise this hesitation whilst encouraging a public service. There are two broad scales at which the promotion of green roofs can take place: country scale and city scale.

On a country scale we have standardised sustainability rating tools to promote the uptake of environmentally friendly infrastructure at the city context. Studies conducted show that most tools have been derived from the first three sustainability rating tools to be implemented. These include the BRE Environmental Assessment Method (BREEAM) in the United Kingdom developed before 1996, Leadership in Energy and Environmental Design (LEED) in the United States developed in 2000 as well as the Green Star in Australia developed in 2002. All of these tools use a set of criteria to score a development in relations to its level of sustainability.

Part 1

At a city scale financial incentives are normally a way to encourage green roof projects. These can be either direct (subsidies or grants) or indirect (non-capital compensation such as density bonuses). On the other hand policies can be used to enforce green roofs. Here we have performance (stormwater management) or technology (specific technical requirements for any given building) policies. With the use of these different types of policies and incentives I took a look at four international and two national case studies to compare the state of green roof implementation in every given location. What I found was very interesting!

Main Source: Booysen, K. 2013. Aspects that encourage the successful integration of Green Roofs in cities: Policy Issues and Green Roof Specialist Perceptions, Dissertation submitted in partial fulfilment of the requirements of the Degree in Master of Philosophy in Urban Infrastructure Management and Design, Department of Engineering and Built Environment, University of Cape Town.

Also see: Green Roofs: International Inspirations + Green Roofs: Local Realities