Comparative Analysis of Thermal Bridges and Condensation Risk Based on Installation Positions of Single- and Double-Window Systems in Externally and Internally Insulated Concrete Walls

This study investigates the thermal bridge characteristics and condensation risks associated with the installation of single- and double-window systems in externally and internally insulated concrete walls. A total of twelve configurations were evaluated by combining two window types, three installation positions (exterior, middle, and interior), and two insulation strategies. Two-dimensional and three-dimensional heat transfer simulations were conducted using ISO 10211- and ISO 10077-2-compliant methods. Both linear (Ψ) and point (χ) thermal transmittances—including those caused by mechanical brackets—were considered to derive the effective U-value (Uw,install) for each case. The results showed that placing windows on the exterior side of the insulation layer yielded the best thermal performance, while interior installations posed a higher risk of surface condensation, particularly for single windows. Although single-window systems generally exhibited superior intrinsic insulation, their thermal performance degraded more significantly than that of double windows when installation-related thermal bridges were included, especially under interior-side configurations. Additionally, the study applied the DIN 4108-2 guideline, which recommends a 30 mm insulation overlap around window frames. The application of this detail reduced thermal bridging across the evaluated configurations, with the magnitude of improvement varying depending on window type and installation position. This study provides simulation-based insights into the performance impacts of window installation details and highlights the importance of thermally optimized design strategies to minimize heat loss and condensation in high-efficiency building envelopes.