The built environment has an important role to play in sustainable development. The Dutch government estimates that the build environment is responsible for 50% of resources used, 40% energy use, 30% of water use, 35% of CO2 production and 40% of the total waste production in the Netherlands. Because of these relatively high numbers, changes in the build environment can have large impact on the sustainability of our society. At this moment about a hundred thousand dwellings built during the 1960 -1970 are reaching the age of 50 each year making more than 50% of the Dutch building stock older than 50 years. In the current Dutch building stock, only a small portion of new buildings is added every year. At the current rate of 0.4% it would take 250 years before all buildings would be renewed. The average lifetime of a residential building is 50 years. This can be extended another 50 years with the right intervention. It is therefore very important to have a solid strategy to deal with existing buildings as this can play an important role in maintaining a high-quality building stock while working towards sustainable goals. This thesis looks at the challenges of high rise residential flats built in the post- WW2 era of the 1960’s in order to develop a refurbishment method that can help to upgrade and maintain these types of buildings in a sustainable way. By keeping the buildings instead of demolishing or replacing them resources and energy can be spared and by refurbishing them a more sustainable building stock can be achieved. The chosen refurbishment method is an add-on strategy as this deals with many challenges the flats are facing. Using the parameters from the case study project the Leeuwerik flat in the Poptahof, add-on variants have been designed with big emphasis on flexibility, demount ability and durability. The Add-ons aim to improve the physical building qualities by providing better thermal performance. They improve the spatial qualities by providing extra space and they improve the social quality of a building by provide a new and more diversified look. The three main add-on variants are categorised by material namely wood, concrete and FRP. The add-ons have been detailed to be completely prefabricated and to be quickly mounted on the building. The performance of each of the addons has been assessed in order to compare them and to find out what the influence is of the material choice on add-on dimensions, the thermal performance the and the environmental performance. Overall it can be concluded that using a demountable add-on strategy is a feasible way to quickly refurbish a building. It offers a way to deal with existing building physical problems and can improve the architectural and spatial qualities of an existing building. Different add-on types and construction materials and are possible. This leaves a lot of space for designers that want to use the demountable add-on strategy while working on a refurbishment project of a high rise residential building to make their own choices depending on the focus of the project, giving each building a unique appearance. This will lead to a higher quality and more sustainable building stock in the long run.

The Netherlands is currently facing an overloaded housing market. This has the consequence that many people cannot find a suitable dwelling. To solve this issue the government made the plan to build one million houses between 2020 and 2030. Apart from the quantitative problem of too little houses what is even more important is to figure out what type of houses to build. Where should the houses be build? For whom should they be build? How do these people want to live? These questions need to be answered to make certain the houses that will be build have the potential to solve the housing shortage. Demographic data of The Netherlands and the design location the city of Rotterdam shows that most household growth in the coming years will occur among families with children and singles of all age categories with the largest increase in the 65+ age category. Looking at the current housing situation of families and elderly people living in the city it seems like there is already a shortage of suitable housing. With the prognosis pointing out that there will be a growth in these households the shortage will only get worse unless action is taken. Living environment plays a crucial role in people’s lives especially in the most vulnerable parts when growing up as kids or when nearing the last stage of life. This is because when we are young but also when we grow old we are dependent on caregivers and on what our direct environment can offer to meet our needs. This thesis therefore looks into an intergenerational housing approach based on the thought that by creating buildings in such a way that they help with bringing people together and by creating inclusive communities many issues concerning families and elderly people living in the city can be alleviated. The building design serves as an example for the many opportunities there are to improve life in the city by keeping people in mind instead of only focusing on creating more houses to solve the housing crisis. By taking this approach it is possible to get to a much more long term sustainable solution for the housing crisis benefitting all the participants and leaving a much larger positive impact on the whole of society.