Thermal bridge

A thermal bridge is an area of the building envelope where heat is transferred to the outside faster than through the surrounding building components. This leads to increased heat loss, lower surface temperatures and potential risks of moisture and mould formation. A thermal bridge is therefore considered a thermal weak point in the building envelope. Thermal bridges affect the energy efficiency of a building and play an important role in energy-efficient renovations, energy performance certificates and building physics assessments.

Info: The technically correct term is thermal bridge. Cold bridge is often used colloquially as a synonym, but it describes the same building physics effect.

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Why are thermal bridges important?

• Reducing energy losses: Thermal bridges increase a building’s heating energy demand through additional heat loss.
• Improving living comfort: Cold surfaces and draught effects can be avoided.
• Minimising moisture and mould risks: Low surface temperatures promote condensation and therefore increase the risk of mould.
• Optimising renovations: Thermal bridges are often crucial for the effectiveness of energy-related measures.
• Supporting documentation and funding: Taking thermal bridges into account is part of many energy calculations.

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How do thermal bridges occur?

Thermal bridges occur wherever thermal insulation is interrupted or where heat can spread differently than in the rest of the building component, for example at junctions, external corners or penetrations.

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Structural thermal bridges

Components with higher thermal conductivity penetrate the insulation layer.

Examples:

• Balcony slabs without thermal separation
• Steel beams
• Fixing elements
• Cantilevered components

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Geometric thermal bridges

The shape of a building leads to increased heat flow.

Examples:

• Building corners
• Roof connections
• Window reveals

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Material-related thermal bridges

Different building materials within one component conduct heat to different degrees.

Examples:

• Concrete columns in insulated external walls
• Steel components
• Uninsulated junctions

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Execution-related thermal bridges

Planning or installation errors lead to local weak points.

Examples:

• Missing insulation
• Gaps in insulation material
• Leaky junctions
• Incorrect window installation

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How thermal bridges are detected

• ‍Thermography: Thermal imaging cameras make temperature differences on building component surfaces visible and help locate thermal weak points in order to detect thermal bridges.‍
• Thermal analysis: The thermal imaging data is assessed together with building information and building physics relationships.‍
• Digital building data: Point clouds, as-built models or digital twins enable the spatial assignment and documentation of thermal bridges.‍
• Building physics calculations: Calculation models help quantify the influence of thermal bridges on energy consumption and classify heat losses.

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What are the consequences of thermal bridges?

• Higher energy consumption: More heating energy is lost through thermal bridges than through comparable, correctly insulated areas.
• Lower surface temperatures: Internal surfaces can be significantly cooler than adjacent building components.
• Condensation: If the surface temperature falls below the dew point, moisture can condense, especially in cold junction areas.
• Mould formation: Persistent moisture increases the risk of microbial growth and visible mould.
• Building damage: In the long term, moisture exposure can damage building components and materials.

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Quality criteria for thermal bridge analysis

• Documented measurement conditions and temperature differences
• Suitable thermal imaging recordings
• Consideration of the building construction
• Traceable assessment of the causes
• Connection with as-built and building data

A thermal image alone is often not sufficient. Only professional interpretation enables reliable conclusions.

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Typical mistakes

• Automatically assessing every temperature deviation as a thermal bridge
• Carrying out thermal imaging under unsuitable weather conditions
• Interpreting reflections as thermal anomalies
• Failing to distinguish between moisture and thermal bridges
• Assessing results without knowledge of the building component structure

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Thermal bridge vs. cold bridge

In everyday language, both terms are often used synonymously.

Thermal bridge

• Technically correct term
• Describes increased heat flow through a building component

Cold bridge

• Colloquial term
• Describes the perceived cooling on the inside surface

In building physics, the term thermal bridge is predominantly used.

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Thermal bridges and energy-efficient renovation

Reducing thermal bridges is one of the most important measures in energy-efficient renovation. Improved junction details, continuous insulation layers and thermally separated constructions help minimise energy losses and sustainably increase building efficiency.

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