The life cycle of a building has a tremendous impact on the environment. This is due to its energy demand, production and transportation of building materials, and its maintenance. Actually, the building industry is one of the most polluting industries that contribute to climate change. In the Netherlands alone, this sector is chargeable for 50% of the materials consumed, 40% of the total energy used and 35% of the total CO2 emissions. To limit the effects of climate change, the Dutch government has set several requirements for new buildings concerning energy use and emissions. The energy performance of buildings is a requirement to minimise the energy demand of buildings. The environmental performance is a requirement to reduce the environmental impact of materials used in the building. These requirements correlate negatively. Therefore, when the regulations get more strict, it will not be possible to satisfy both. Thus, the requirements will adversely affect each other. This thesis ‘When energy savings become a waste’ describes research about the design of facades to increase the sustainable performance of office buildings steered by the regulations energy performance of buildings and environmental performance of buildings. It is about the conflicting demand and how to design a facade in such a way that no energy will be lost because the energy reduction is less than the energy needed for the production of an element. The main research question that is answered in this research is ‘How can the Dutch building industry achieve sustainable buildings by designing according to both the energy performance and environmental performance of buildings applied on facades?’ First of all, the relation between sustainability, energy performance-, environmental performance- and circularity of buildings is established. In this research, sustainability is defined as a goal to minimize harmful emissions to the planet. This goal can be achieved in different ways , one of which is the circular building principal. A circular approach of building aims to no longer use new resources and produce no more waste. The energy performance of buildings and the environmental performance of buildings can help steer towards sustainable buildings. Next, the concepts of the environmental performance of buildings (MPG) and the energy performance of buildings (EPC) are introduced, and their current use in methods and tools is analysed. Several methods exist in which the energy performance and the environmental performance are combined. For this research, the ‘sustainability performance of buildings’ (DPG) will be used, which is an objective method combining the energy and material by converting the total CO2 emission in the energy performance to shadow costs and by adding this to the shadow costs as calculated in the environmental performance. Therefore, the sustainability performance indicates the total emissions of the whole life cycle of a product, process or building and the total costs required to bring the environmental impacts of a product, process or building to an acceptable level. The sustainability performance of buildings is expressed in shadow costs per square meter, €/m2. In a one-factor-at-the-time analysis, the environmental- and energy performance of buildings is calculated in different scenarios with a varying parameter in the design of the facade. For this analysis, a reference office building was used as a study case. This is a medium-sized office building with a curtain wall facade of aluminium and triple glazing. Eight variants are examined, in particular: type of glass, insulation value and insulation material, the ratio of open and closed parts in the facade, use of PV-panels on the facade, sun shading, facade composition, orientation and changing the building process from linear to circular. The most important results of the case study are as follows: •In types of glazing, vacuum glazing has the best sustainability score. Also, triple glazing with a total glass thickness of 12 mm is an improvement compared to the current thickness of 16 mm. The performance of HR++ glazing is only 1% worse than triple glazing and can, therefore, also be considered in use. •The insulation value, as well as the insulation material, has no significant influence on the sustainability performance. The reduction in energy by adding more insulation material is almost equal to the energy needed for the production of the extra material. •The percentage of glass in the facade has a tremendous impact on both the environmental performance and energy performance. Both the performances get worse with a higher percentage of glass. The trend in the design of office building is, however, to increase the percentage of glass. •The use of PV panels in the facade is beneficial for the sustainability performance. The revenue is small for PV panels on the north facade, and the investment will not pay off. In the other orientations the PV panels the payback time is between 11 and 15 years. PV panels on the south facade achieve the most improvement. •The addition of sun shading will only slightly improve the sustainability performance when no louvres are included in the design and the control system is optimal to reduce the heating and cooling demand. •A change in the facade system and materials can significantly reduce the sustainability performance. However, this is mainly caused because no louvres are added in the other facade designs. Therefore the addition of louvres is not sustainable; neither is increasing the height of the floors. The facade with wooden cladding has the best sustainability performance. •The orientation of the building can influence the sustainability performance without changing other parameters. For the reference building, the most optimal orientation is achieved by a rotation of 90 degrees. The windows are then orientated north and south. •The effect of different circular scenarios is calculated and compared to the reference scenario with a service life of 50 years. The scenario considering the reference situation with a realistic service life of 20 years, has the highest score of all. In the next scenario, the percentage of reuse is increased to 60% and the service life of the facade is 20 years, resulting in an improved sustainability performance of 2%. In the last scenario, the service life is extended to 100 years, causing an improvement of 4%. Conclusions of this research are only based on the sustainability performance and do not take into account social and financial aspects. Therefore in some variants, the most sustainable solution might not be feasible in practice. For example, vacuum glazing is very expensive, and consequently, triple glazing with a thickness of 12 mm is advised to use. One realistic variant is calculated with a combination of variants. In this scenario, financial and social feasibility are taken into account, and an improvement of 15,5% is achieved, showing the value of this integral approach. Based on this research, it can be concluded that the Dutch building industry can achieve sustainable buildings when the design is focused on decreasing the sustainability performance of buildings. An integral approach considering both energy and material use is essential when enhancing the sustainability performance of buildings. The goal of the Dutch government to steer on CO2 emission can help to improve the sustainability performance. However, the relationship between the sustainability performance and CO2 emission is not entirely linear. Energy and material use need to be balanced together to accomplish a sustainable built environment. To be able to use this knowledge in a broader context it is recommended to conduct this research for a combination of the used variants, take into account design aspects of the whole building, and perform analysis on multiple buildings. In this research, only the aspects of sustainability concerning the planet are taken into account. Aspects regarding people and profit should also be considered to determine the feasibility of sustainable measures.