Gaining approval for individual roofscaping projects has proven to be a challenge for the initiative given that 70% of properties in Rotterdam are privately owned. This makes citizen approval an essential goal of the project. In 2010, however, citizens had reservations about installing roofscapes. To further complicate the matter, building regulations are drafted on a national scale, so Rotterdam does not have the legislative means to establish standards for roofscape development. So, without zoning laws or building codes to set a precedent for this kind of project, the initiative must convince city planning officials and the public that roofscapes are a worthwhile investment. The City has also faced the challenge of onboarding enough investors to meet their targets given that roofscape projects have a payback period of up to 20 years, which is much longer than more traditional capital projects. Ultimately, addressing this obstacle has proved to be a productive endeavor and has resulted in the beginning of a reconceptualization of how the costs and benefits of sustainable projects should be evaluated.
The Rotterdam Roofscape programme has developed schematics for four different classifications of multifunctional roofs. Blue roofs emphasize water retention, green roofs cultivate biodiversity, yellow roofs provide clean energy production, and red roofs work towards social cohesion. By installing a mix of roof types, the City has been able to approach climate action with a holistic mindset. Yellow roofs generally utilise PV panels and wind turbines to actually generate energy, while green roofs reduce cooling needs –– the two can be combined to expedite the process of reaching zero emissions status for individual buildings. The plan is clear and specific and has an itemised list of 40 specific steps falling into 7 action lines –– which break down into goals of informing, inspiring, stimulating, developing policy, connecting, and innovating.
In total, the project aspires to build 1 million m2 of multifunctional roofs by 2030. In 2017 and 2018, the initiative hopes to install 10,000 m2 of yellow roofscapes to generate 1.25 MW of renewable energy and 80,000 m2 of green roofscapes to cool buildings by 3-4°C and retain up to 2,000 m3 of water. Water retention reduces water treatment costs by $75,000 annually and alleviates the burden of runoff from the sewage system in the city centre, reducing the local flood risk. The project has already built 250,000 m2 of green roofscapes which have retained 5,000 m3 of water in addition to providing public health benefits by greening spaces in and around hospitals.
The Rotterdam Roofscape programme presents replicable and scalable solutions to climate change which can be incorporated into any city’s regular operation to provide environmental benefits and add value to capital projects which would be underway anyways.
The success of the Rotterdam Roofscape programme can be leveraged as a means of shifting the conversation surrounding the costs and benefits of sustainable projects. Beginning to evaluate such initiatives in more than financial terms, instead focusing on less quantifiable benefits such as public wellbeing, air quality, and long-term resiliency, is an important step toward prioritizing sustainability in all municipal projects.