The existing building stock’s major energy use and climate impact has led to increased interest in energy renovations, especially in cold climates causing high heating demand. In Sweden, deteriorating windows are a common issue that property owners must act on. However, there is an array of possible window interventions, including maintenance and replacement. These interventions differ in material and operational energy saving potential, leading to trade-offs between the product and operational stages in terms of costs, climate impact and energy use—three key life cycle (LC) dimensions for sustainable renovations. Addressing these sustainability dimensions is crucial for renovations to align with Sweden’s climate and energy goals. Also, focusing on solely total climate impacts over a set period may overlook long-term trends, especially considering the future dynamics. This work aims to extend the knowledge of the life cycle impacts of window maintenance versus replacement for residential buildings in cold climate regions. It addresses two key questions: how window maintenance and replacement compare in terms of LC climate impact, energy use and costs, and how they compare with a temporal perspective of accumulated climate impacts. 

Two studies on window maintenance versus replacement form the basis of this work, both estimating the interventions’ LC climate impact (expressed in global warming potential, GWP) and costs, in line with European standards for life cycle assessments (LCA) and life cycle costing (LCC). The second study expands the first to an additional building and adds more sensitivity analyses. This thesis further extends the first studies by adding two new perspectives. First, the energy resource perspective is integrated by estimating the window interventions’ life cycle energy (LCE). Second, the temporal perspective is considered by assessing the annual climate impacts and savings from each intervention, while factoring in a transition to climate-neutral heating. 

Results indicate a stronger relationship between life cycle climate impact (LCA-GWP) and energy use (LCE) compared to costs (LCC). This derives from the direct impact of primary energy sources on climate impact, and because operational savings weigh more heavily in the LCA-GWP and LCE outcomes than the LCC. With low energy prices and high investment costs, no window intervention is cost-effective. The lower cost option between maintenance and replacement depends on the individual building. The temporal perspective reveals whether the life cycle climate impact has a positive or negative trend, a key consideration in transitions to climate-neutral heating energy mixes. With future low-carbon heating, more efforts should be put on reducing material use than heating demand, as recurring embodied impacts increase in importance over time. 

Ultimately, the preferred window intervention—maintenance or replacement—depends heavily on the building and its context. Window replacement may support energy-saving targets if prioritized for poorly insulated buildings with high-carbon heating, especially in cold climates. Maintenance may be preferable for well-insulated buildings with low-carbon heating. This research provides valuable insights for decision-makers pursuing sustainable renovations, emphasizing the potential benefits of maintenance in certain contexts.