The construction industry today generates a significant amount of waste. Much of this comes from demolition projects, where a large portion of the material is still of high enough quality to be reused. This study investigates whether it is possible to plan for the reuse of demolition materials already in the planning phase. To do this, the materials need to be classified so that their properties are known. The study is limited to examining wood as a material.The thesis aims to develop methods for assessing the condition of built-in wood, with the purpose of identifying and developing methods to evaluate the strength and stiffness of built-in wood. This is relevant both for determining strength classification during renovation and for classifying wood material intended for reuse. The goal is to establish specific methods and determine if they can be applied to an existing building.The chosen method is based on the idea that the modulus of elasticity (E-modulus) for a wooden beam should be well correlated to the E-modulus for a small chip from the same piece of wood. This is calculated using resonance vibration in the wood material, which is a well-established method. This is supplemented by visual assessment based on knot size and other defects in the material. If this relationship holds, the strength and E-modulus of an entire wooden structure can be assessed through a small wood chip.The theoretical section addresses the waste management practices of the Swedish construction sector and the need for circular flows. The reuse of building materials, especially wood, is highlighted as an important factor in reducing waste and environmental impact. By reusing wood, the need for new production decreases, contributing to sustainable development. The study builds on previous research that identifies the need for non-destructive methods to assess the condition of built-in wood. This is particularly important because many existing methods are not suited for wood with remaining fasteners or other defects that arise during dismantling.To summarize, the thesis presents a comprehensive study of methods for assessing the condition of built-in wood, with a focus on strength and reuse. The study covers both theoretical and practical aspects of sustainable building practices and offers valuable insights for future research and implementation in the field. The study indicates that it is possible to estimated the E-modulus of structural timber based on the E-modulus of a small defect-free chip cut from the board. Knots and associated grain deviation seems to lower the global E-modulus with only 10-15%.