Thermal bridges (thermal anomalies) in a building envelope are any intentional or unintentional design or construction detail that may cause significantly more energy loss through the building envelope than intended. Thermal performance of any building component may be significantly degraded by thermal bridges. The material presented here only introduces the topic. Reports by Silvers et al. (1985), Silvers and Tye (1985), and Melton et al. (1987) review the current understanding of thermal bridge problems, techniques for analyzing the heat transfer due to thermal bridges, and methods to reduce the energy losses due to thermal bridges. Other references include the ISO Standards 6946/1 and 6746/2 on building thermal calculation methods (ISO 1986a, 1986b), the non-computerized thermal bridge calculation procedure by Staelens (1986), and the translations of Berthier (1973) and Johannesson and Aberg (1981).

A thermal bridge can exist for many reasons. Structure components such as concrete floors and pillars in commercial buildings may act as thermal bridges. In residential buildings, floor, ceiling, and roof joists may be thermal bridges. Fire breaks may also result in a building envelope with significant thermal bridges. A good example is the use of steel studs in both internal and external walls. ASHRAE recognizes this problem in Standard 90.1, which includes envelope thermal transmittance correction factors for roofs and wall assemblies that contain metal framing. The correction factors can reduce the effective R-value of the insulation by 45-60% for walls and 67-88% for roofs. Metal beams, metal pipes for building water supply, fire protection,...