In recent years the research group of Building Physics at Tampere University of Technology (TUT) has conducted two major research projects concerning airtightness of residential buildings in Finland. During these studies it has been discovered that most Finnish single-family houses do not reach the n50-value recommended in the National Building Code of Finland. Airtightness is mainly a property of the building and not the structure. It depends on the design and especially the execution of constructions and joints. Building envelope’s airtightness depends mostly on how well different structures (e.g. base floor and external wall) are joined together. Window and door connections and penetrations can also inflict an air-leakage on a building envelope. It was also discovered that updated information of how to ensure building envelopes airtightness with constructional details was not available in Finland. As a part of the research project Airtightness Of Heavyweight Detached Houses, TUT decided to publish a guidebook of airtight constructions and joints. The guide presents both detailed plan drawings for the designers and working instructions for the construction site. The examples are of concrete elements, wood-framed, block and masonry constructions. The guide concentrates on residential single-family houses but the solutions can be adapted to other buildings as well. Solutions are developed in a group of researchers from different fields of structural engineering and commented by the construction industry professionals in the executive group of the research project.