In the process of urbanization, cities are becoming ever larger and denser, a process accompanied by a dramatic decrease in water permeable surface area. In addition to this, due to climate change, several areas are experiencing extended periods of heavy rainfall and serious droughts, resulting in an increasing water problem in many cities. A major challenge is to find a good balance between measures preventing an overload of rainwater leading to urban flooding and providing a solution for times when there is a scarcity of water, which currently result in unwanted effects like restrictions for water use. The Dakdokters is a company that works on a solution for these problems using an underused place, rooftops. Their core business is designing and installing green roofs in order to increase the benefits of greenery in cities. In 2013 they realized that their green roofs could maybe be combined with an open water storage system that could serve as a water buffer. This was the start of a project called “Polder Roof” (polderdak). The Polder Roof makes use of a WRB (Water Retention Box) layer underneath a green roof. Large amounts of rainwater which would normally be discharged in the sewage system, are temporarily stored in these boxes on the roof. This not only reduces the pressure on the sewage system during periods of heavy rainfall, but the stored water can subsequently be used for e.g. irrigation of the green roof, or for applications like toilet flushing, leading to a decrease in the use of high quality tap water. Technically it is necessary to be able to precisely control the amounts of water stored. This is achieved by a semi-automatic system, called the Smart Flow Control (SFC), which uses various sensors and electric actuation for control. In addition, it can be controlled over the internet by external operators. Assignment Currently several prototypes of SFC controlled Polder roofs are installed on 7 different rooftops in Amsterdam. These prototypes function as a proof of concept. However, for the final market implementation some parts of the concept need improvement: First of all there is the costs aspect. In order to be competitive with other water retention solutions, the Polder Roof should become less expensive per m3 of water storage. A decrease in investment costs as well as in the yearly costs of maintenance and data subscriptions are needed. Secondly, the current products fail too often, leading to high maintenance costs. Thirdly, although not important when it comes to functionality, the design of the system must be aesthetically pleasing, especially in cases where the green roof is going to be combined rooftop park-like settings on the rooftop, visited by e.g. personnel of companies. The assignment of the Dakdokters for the project described here, focused foremost on the design of the regulatory valve and its housing. In the course of the project the rest of the system was also analysed to identify any other optimizations needed. The outcome of the project can be divided in the following analyses and results: Step 1: Exploring the context The input of different stakeholders was obtained in interviews, especially with a view to critically assess the wanted functionalities of the Polder Roof, since a reduction in these could possibly result in a less complex product, reduced parts costs and increased reliability due to less parts that could fail. Not just the market context, but also the technological implications of the roof context was analysed. Step 2: Analysis of the current product All current parts were critically analysed with respect to their functionality, costs and reliability. The reliability analysis not only comprised to regular wear through usage, but also to sensitivity to external factors, such as water pollution. These analyses corroborated the idea that the biggest improvements could be made by redesigning the valve and housing of the SFC, concomitantly also improving the installation procedure. The latter is important since in many cases multiple SFC’s need to be placed , due to the fact that roofs are never totally flat but have a slight slope, requiring multiple basins , each with their own SFC for the optimal water storage. Therefore I first concentrated on redesigning the valve and its housing. Step 3: Analysis of the current product These analyses led to a personal design vision of the full system. Together with a function map that was checked by the company and its most important partner, Optigroen, this resulted in a complete overview of all desired functionalities of the new Polder Roof and a program of requirements. Step 4: Product development of the valve and the housing. Multiple brainstorm sessions resulted in several new ideas, which were evaluated in expert meetings, using prototypes and (CAD)-sketches. I designed a new way of operating the valve, using a rotational actuator. The expensive, non-functional and not very aesthetically pleasing windmill shape of the current housing was simplified into a droplet shape, making it cheaper to produce while still being iconic. This housing was optimized for easy manufacturing and installation and improved safety of the system. These concepts were bundled into a final new concept. Step 5: Embodying the concept In the final design phase the concept was further embodied. Several optimizations using tests with a full scale prototype and meetings with experts led to final concept of the SFC which is focused on an easy and cost-effective production and installation process. A concept for the parts needed for the connectivity of all SFC’s on the roof, using a new micro-controller, reducing the investment and yearly costs and a new scenario for the software using rain radar data was designed. Step 6: Evaluation of the new product. In the final phase an evaluation was done on the functionality, the reliability, the costs and the aesthetics of the new design. These evaluation proved that a the new design is less expensive, easier to install on different types of roofs, easy to maintain and more reliable. In addition, it proved aesthetically pleasing to the stakeholders. Apart from these conclusions the results of these evaluations led to recommendations for further development of the SFC, of which the most important is the following: In order to accurately test the new design it is necessary to built a full size test set up with which roof conditions can be simulated. This set-up should including multiple variations in roof lay-out and amount of water storage. It can similarly act as a demonstration model