Vertical extensions and heritage values The construction sector entails a significant environmental and climate impact, with large raw material consumption and waste production and huge emissions of greenhouse gases. More sustainable ways of meeting our need for buildings can include prolonging the life span of buildings. This requires buildings to be flexible and adaptable to changing needs. The Timber on top project investigates how vertical extensions to existing buildings can achieved in a way that is sustainable socially, ecologically, and economically. The broader aim of this study is to support sustainability in the building and construction sector. The goal is to map and compile practical knowledge on how heritage values are best considered in vertical extension processes. Methods used are literature studies, a workshop, and interviews. The results show that obvious parts of a good practice are to involve competence on building conservation in the process, to follow up and control heritage values in the construction process, to ensure that there are control points in the control plan and that these are followed up. Specifically, different advice can be given for different stages in the construction process. Best practice in the idea stage Examine the conditions of the object already in the idea stage. Contact an antiquarian early for informal advice. Examine whether the object is sensitive or not and whether it is a house that is suitable to extend vertically or not. In connection with pre-study work, carry out an investigation on the object’s heritage values. Let the antiquarian take part in various investigations that are made. For extension projects, it is especially important to also have a structural engineer involved early in the process. Superstructures can lead to several types of measures that affect heritage values: reinforcement of load-bearing parts, measures for fire protection and measures for noise protection. At an early stage, different design alternatives can be explored, and technical requirements and cultural values can be weighed against each other. Hire an antiquarian who gets an integrated role of sounding board in early investigations and who can support an architect. Best practice in the planning stage and implementation stage Initially, when the consulting group is put together, make a presentation of the building and its heritage values. Take a tour of the site with everyone involved. Strive for continuity in the consulting group to avoid recurrence in the dialogue. Bring all important skills with you early. Include an antiquarian in the implementation phase. Checkpoints must be followed up. Contribute to the expert antiquarian coming out on the construction site to follow up the control plan. Strive for a good dialogue, where all interests come together.