Thermal Bridge / Cold Bridge

A thermal bridge (also called a cold bridge) is a localised area in a building’s structure where heat escapes more easily than through the surrounding material. These cold spots occur where the insulation layer is interrupted, reduced, or bypassed — allowing heat to flow from the warm inside to the cold outside.

Common examples of thermal bridges

• Steel lintels — the steel lintel above a window or door conducts heat much faster than the surrounding brickwork
• Window and door reveals — the edges around windows and doors are often poorly insulated, especially in older properties
• Where walls meet floors or roofs — junctions between different building elements are classic cold bridge locations
• Structural beams — steel or concrete beams that pass through the building envelope
• Wall ties — the small metal ties that connect the inner and outer leaves of a cavity wall
• Balcony connections — a concrete balcony slab that extends through the external wall

Why thermal bridges matter

Thermal bridges cause two practical problems:

1. Heat loss

Even a well-insulated wall can lose a significant amount of heat through thermal bridges. In a typical UK home, thermal bridges can account for 20-30% of total heat loss — undermining the benefit of the insulation you have paid for.

2. Condensation and mould

When a surface is colder than the surrounding area, moisture in the air condenses on it — just like a cold glass on a warm day. This creates the conditions for mould growth, which is a health risk and damages finishes. If you notice black mould appearing in corners, around window edges, or at the junction of walls and ceilings, a thermal bridge is the likely cause.

Addressing thermal bridges during renovation

If you are upgrading your home’s insulation or replacing windows as part of a renovation, addressing thermal bridges at the same time is essential — otherwise you are solving one problem while leaving another untouched.

Solutions include:

• Insulated lintels — replacing old steel lintels with insulated cavity lintels
• Window reveal insulation — wrapping thin insulation around the edges of window openings before plastering
• Continuous insulation — ensuring the insulation layer is unbroken across junctions (wall-to-roof, wall-to-floor)
• Thermal break strips — insulating pads placed between structural elements and the building fabric

Discuss thermal bridges with your general contractor or architect when planning insulation upgrades. Addressing them adds modest cost during construction but is far more expensive and disruptive to fix after the project is finished.