We are living at a tipping point of human civilisation. Our impact on the climate has become undeniable and if we don’t want a drastically different way life, we must adapt. The building sector is responsible for around 19% of the total CO2 emissions and 30% of the energy use in Sweden. To lower that amount, we need to build smarter. To design a sustainable building, we need a holistic approach that consider several factors. This thesis discusses the concept of sustainability and the sustainability factors that influence the design of a building.  By using a range of certification systems, such as EU level(s) and Miljöbyggnad 4.0 we can evaluate the design in an early stage to avoid neglecting any vital aspects of sustainability. Furthermore, the concept of adaptability as a source of sustainability is explored, and a design for a modular house that is both sustainable and affordable is proposed.