Numerical analysis of heat transfer and surface condensation risk in the plinth zone of basement-included building

This study investigates the thermal-moisture performance of the plinth–basement joint in buildings with unheated basements through steady-state numerical simulations using both two-dimensional (2D) and three-dimensional (3D) models. Eleven design variants were analyzed, differing of the thickness of the thermal insulation of the plinth zone and the length of its embedment in the ground. The simulations were conducted in accordance with PN-EN ISO 10211 and PN-EN ISO 13788, with boundary conditions based on the climatic data for the city of Poznań. It has been demonstrated that an incorrect thermal insulation solution in the plinth zone can result in condensation on the interior surface of the envelope, leading, among other consequences, to the development of mycological changes. At the same time, significant differences in the temperature factor determined by the two and the three-dimensional models were pointed out. The effect of each solution on the value of heat transfer coefficients and temperature in the unheated basement space was verified. The findings confirm the necessity of 3D analysis in assessing complex joints and provide quantitative guidance for optimizing insulation in the plinth zone. The results can serve as a basis for the development of design recommendations aimed at minimizing thermal bridges, improving thermal comfort, and reducing energy losses in retrofitted and newly designed buildings.