kylmäsilta

Kylmäsilta, literally “cold bridge,” is a term in building physics describing a thermal bridge: a path of increased heat transfer at structural junctions where the building envelope is interrupted or materials with different thermal conductivities meet. This causes heat to flow more easily from indoors to outdoors than through the insulated parts, leading to higher heat losses, lower energy efficiency, and a higher risk of condensation and mold in climate zones like Finland.

Common locations include wall–slab junctions, corners, jambs around windows and doors, balcony and balcony–wall connections, roof edges, and penetrations through the envelope. The effect is quantified in energy calculations by linear thermal transmittance (Psi) along a junction and by point transmittance (Chi) at discrete details; together with the overall heat loss factor they influence energy performance certificates and building regulations.

Mitigation focuses on design strategies that maintain insulation continuity and introduce thermal breaks. Examples include using continuous insulation across junctions, non-conductive or thermally broken connections between structural elements, warm edge spacers for glazing, and careful detailing of balcony connections to minimize heat flow across cold bridges.

In Finnish practice, kylmäsilta is a standard consideration in energy-efficient construction and is addressed in building codes, energy-performance assessments, and construction drawings. The term is used alongside broader concepts of thermal performance and building envelope detailing.