This study investigates the durability of timber buildings through a systematic literature review and a service life assessment of two representative building components. The review focused on degradation mechanisms, reasons for demolition, reference service life values, and strategies for extending service life. The deterioration of timber was found to be primarily driven by biological, physical, and mechanical processes, with moisture as a critical factor. Although degradation mechanisms are thoroughly documented, evidence concerning the physical lifespan of timber buildings remains scarce. Most demolitions are due to obsolescence and inadequate maintenance rather than structural failure. Reference service life values are frequently derived from expert judgment and often lack transparent boundary conditions. Nevertheless, factor-based service life prediction models offer a framework for evaluating structural components. When applied to a reference building, the method yielded estimated service lives of 100 years for an interior LVL beech column and 81 years for an exterior wall stud. These findings align with observed lifespans reported in demolition studies. More robust empirical data on demolition ages and refined reference values under standardized conditions are needed. Such improvements would enhance the accuracy of service life prediction models, support more realistic environmental assessments, and strengthen the role of timber as a sustainable construction material. 4. Evaluation of the Expected Service Life for a Reference Building This section applies the findings of the SLR to a practical case study by estimating the ESL of two structural timber components in a reference building. Using the model by Bahr and Lennerts [ 110] identified in Section 3.3.4, ESL values are calculated for one interior LVL beech column and one exterior wall stud in a prefabricated timber panel wall. 4.1. Building and Component Description The reference building () is a three-story office structure constructed primarily in timber by Adams Holzbau-Fertigbau GmbH and completed in 2022, from which two representative structural components are selected for detailed analysis. The primary structural components are made of LVL beech (BauBuche) GL75, used for both columns and beams. The exterior and interior walls are constructed using prefabricated panel construction. The building rests on a concrete base slab, with timber construction above. It is in a temperate climate region of western Germany. Two critical load-bearing timber elements were selected for a detailed service life assessment (): Component A—LVL Beech (BauBuche) Column—Interior, South Side: A beech GL75 LVL column located on the ground floor along the south façade. Positioned inside the building envelope, it is protected from direct weather exposure but receives limited indirect solar exposure through glazing. It is exposed to the indoor climate and remains visible. Component B—Stud in Prefabricated Timber Wall—Exterior Wall, North Side: A C24 structural timber stud from a north-facing external wall panel. Installed within the wall assembly, it is sheathed on the interior side with OSB and clad with gypsum fiberboards as the interior finish. Toward the exterior, it is protected by wood-fiber boards and the façade. The wall encloses a bathroom, and the stud transfers vertical loads within the external wall system. While it does not experience direct weathering, it experiences marginal exposure through the building envelope. 4.2. Service Life Assessment Model The weighted factor method, as proposed by Bahr and Lennerts [ 110], is used to calculate the ESL of the components in the reference building. This model builds on the ISO 15686-3 [ 109] factor method but addresses its limitations through a more structured and conservative approach. A limitation of the model is its design for components with RSL values below 50 years rather than structural components, which the authors note are too costly to replace. The objective of this study is to analyze the service life of timber buildings from cradle to grave. To this end, the model is adapted to a structural component to offer insights into the fixed service life values in environmental assessment and the possible maximum service life values in real-world scenarios [ 110]. The adaptation follows the conceptual structure and weighting logic proposed by Bahr and Lennerts [ 110] but does not attempt a full statistical validation of the model for structural components, which remains an important topic for future research. 4.2.1. Selection of Main and Secondary Factors The first step in the assessment is to identify the primary and secondary factors. Based on the exposure conditions of each component, the following classification was made in . 4.2.2. Defining the Assessment Criteria The assessment criteria were developed based on standards in timber construction wherever possible, to guarantee that the neutral scenario represents a state that is as close as possible to the RSL. In this way, the neutral condition avoids compounding positive or negative influences that may already be present in the cataloged RSL values. Each factor was divided into three scenarios: negative, neutral, and positive, following the Level 1 and Level 2 structure of the model. Level 1 provides a broad and largely material-independent assessment, while Level 2 refines this using more detailed criteria based on standards. In practical application, Level 1 serves as a screening-level approximation, whereas Level 2 is intended to provide a more conservative and reproducible basis for decision-making. Not all criteria allow for a positive scenario. In certain subfactors, adherence to standards is the maximum achievable state; exceeding this does not extend service life (e.g., documentation according to EN 13460 [ 146]). The complete set of criteria is presented in Supplementary Materials, where the assessment forms for the reference components are included. 4.2.3. Categorization of Reference Components The defined criteria were applied to the two reference components: an interior LVL beech column and a structural timber stud in a load-bearing prefabricated timber wall. LVL beech column: Most factors were found to be neutral to positive. A1—Component quality was neutral, with durability class DC 5 rated negative under EN 350 [ 134]. The A2—Material combination was evaluated as neutral. Due to its location within the building envelope, the component qualifies for UC 0 per DIN 68800-1 [ 133], corresponding to a positive influence in B—Protection by design and favorable external exposure E—External physical properties. D—Internal physical properties were neutral in the Level 2 assessment. C—Result of Work Execution and G—Maintenance were neutral to slightly positive, reflecting third-party certification and documentation in accordance with EN 13460 [ 146]. F1—Type of use and F2—Use according to intended purpose were rated neutral. Structural timber wall stud: A1—Component quality was positive due to above-standard grading and adhesive performance, although spruce/fir durability (DC 4–5) contributed a negative sub-assessment [ 134]. B—Protection by design received a positive rating, through a classification in UC 1. C—Result of work execution was assessed positively and D—Internal physical properties were neutral. E—External physical properties were predominantly positive, due to shielding by the façade and wood fiber insulation. F1—Type of use, F2—Use according to intended purpose, and G—Maintenance level were assessed identically to the LVL column, as these factors are largely material- and position-independent and depend primarily on the building’s boundary conditions. 4.2.4. Determining Expected Service Life
