Sustainable construction has in recent years become more important from economical and environmental perspectives. This has led to greater demands on the building energy use, which, among other things, requires good airtightness of the building envelope. Tougher economic conditions have also led to more stringent requirements for increased productivity which has resulted in construction with a higher degree of prefabrication. A high degree of prefabrication can shorten the building time and make the construction more effective. Combining an airtight building with a high degree of prefabrication is challenging. This sets requirements among others on the tightness between the prefabricated elements.The purpose of this study is to achieve a better understanding of how different materials and methods affect the airtightness of a building, as well as the challenges that building construction companies face when combining an airtight building with a high degree of prefabrication. In a literature study different materials and techniques to achieve an airtight building have been studied. The literature study also provides an overview of different methods that are suitable for prefabricated building construction. Six house companies with varying degree of prefabrication as well as one technical consulting company with expertise in passive house and sustainable construction were interviewed. The interviews aimed to find out how companies work with issues regarding airtightness, as well as the challenges and needs companies experience by combining an airtight building with a high degree of prefabrication.The results show that an airtight building can be combined with a high degree of prefabrication. As a premise the airtightness must be ensured during the design with clear instructions of material and technical solutions. It also requires a good knowledge and understanding throughout the organization. As pointed out both in the literature and by the interviewees, sub-contractors often lack the necessary knowledge. The interviewed companies are experiencing difficulties in achieving good airtightness around penetrations, windows, doors and intermediate floors. Another challenge is to use an installation layer while building with a high degree of prefabrication. The study also shows that a good airtightness can be achieved with different materials if proper methods are used. Despite this, the plastic foil is clearly the most common. Most companies request better availability and price of alternative airtight materials. Theory and empirical results are unanimous of the techniques that can be used to achieve good airtightness.