Are you paying more for heating than the size of your house would suggest? Or does damp and mould appear on your walls in winter even though you ventilate regularly? The cause may be a thermal bridge - a phenomenon that does not get talked about much, but which has a direct impact on both your wallet and the health of the people you live with. In this article we explain what a thermal bridge actually is, where in a house it most often hides, and why thermal imaging is the most reliable way to reveal it.
What exactly is a thermal bridge?
A building’s envelope - the walls, ceiling, floor, roof and windows - should function as a continuous thermal barrier. A thermal bridge is a point where this barrier fails: a section of the structure with markedly worse thermal insulation properties than the surrounding area, through which substantially more heat escapes.
Thermal bridges arise from two basic causes:
- The geometry of the structure - corners and the junctions of different building elements naturally have a larger surface area on the outside than on the inside, so heat “flows out” through a larger surface than it flows in from.
- Material passing through the insulation - a concrete ring beam, a steel lintel above a window, or a reinforced-concrete balcony slab conducts heat far better than thermal insulation, effectively “short-circuiting” it at that point.
The result is always the same: at a thermal bridge, the inner surface of the wall is colder than its surroundings, and the outer surface is correspondingly warmer.
How does a thermal bridge cause harm?
Higher heating bills
Thermal bridges are a direct route by which your money - in the form of heat - leaves the house. This is not a negligible amount. In older, non-panel buildings without insulation, thermal bridges at details such as ring beams, lintels and corners can account for 10 to 30 percent of the envelope’s total heat loss. In new or already-insulated buildings, where the rest of the structure is in good order, the share of losses caused by thermal bridges can be even higher - simply because other sources of heat loss have been eliminated and the bridges stand out more.
The result shows up on your gas or electricity bill. The boiler or heat pump has to work harder to compensate for the increased losses, and consumption rises.
Mould and damp
The second consequence of thermal bridges, and the more serious one for health, is condensation and mould. The physics behind it is straightforward: the air in a room contains moisture. If that air comes into contact with a sufficiently cold surface, the moisture condenses out of it - in exactly the same way a glass of a cold drink “sweats”.
The inner surface of a wall at a thermal bridge is typically several degrees colder in winter than the surrounding area. That is enough for moisture to condense there. A wet surface is then an ideal environment for mould to grow, settling in room corners, behind furniture against external walls, or in the recesses around windows.
Mould is not just a cosmetic problem. Its spores spread through the air and can cause allergies, respiratory problems and health complications, especially in children, the elderly and people with allergies. Repainting or chemically treating the surface does not help - the mould will come back until the cause, the thermal bridge, is removed.
Where in a house are thermal bridges most common?
Experience from thermographic inspections shows that thermal bridges recur in the same places regardless of whether the building is an older brick house, a panel-built apartment block, or a new build.
Window reveals and lintels
The area around a window frame - the reveals (the side jambs) and the lintel (the top of the opening) - tends to be one of the most problematic spots. During insulation work, the thermal insulation is often interrupted or narrowed here, or is not brought all the way up to the window frame. There is also often a steel or concrete lintel above the window, which conducts heat far more readily than insulation.
Balcony and loggia connections
Balconies and loggias are the most critical thermal bridge detail in modern buildings. In panel-built houses, the reinforced-concrete balcony slab passes through the perimeter wall without interruption - and concrete is an excellent thermal conductor. This creates what is known as a linear thermal bridge, which draws heat out along the whole length of the slab. In new builds this problem is addressed with special insulating elements (thermal break connectors), but in older buildings it is present almost without exception.
Ring beams and lintels
The floor ring beam - a horizontal concrete element running around the building at the level of each storey - is a classic material-based thermal bridge. Concrete has roughly fifty times better thermal conductivity than mineral wool, so any ring beam without sufficient insulation cover acts as a thermal channel straight from the interior to the outside.
Corners of external walls
The internal corners of rooms, where two external walls meet, form a geometric thermal bridge. From outside, this corner has a smaller surface area than from inside, where it is correspondingly larger. The result is that the surface temperature at the corner tends to be lower than in the middle of the wall, and this is exactly where mould most often forms.
The junction of roof and wall, and the parapet
The point where the roof covering meets the external wall, and in particular the parapet (the raised edge of a flat roof), are other typical locations for thermal bridges. The parapet is exposed to heat loss from three sides at once - from inside and from both outer surfaces. Without a carefully executed insulation detail, heat loss here increases significantly.
How thermal imaging reliably reveals thermal bridges
A thermal camera captures surface temperature and displays it in colour - cooler areas in blue and purple, warmer areas in yellow and red. As a result, thermal bridges show up as clear colour deviations from their surroundings.
When measured from outside (typically by drone), thermal bridges appear as warmer spots on the façade - wherever more heat is escaping, the façade surface is warmer than its surroundings. When measured from inside, thermal bridges appear instead as colder spots on the internal surfaces of walls, ceilings and floors.
Thermal imaging can reveal not only places that are visibly damaged or already affected by mould, but especially those where the problem is only just developing - behind a wardrobe, under plaster, or in a window reveal, for example. This lets an inspector identify a thermal bridge before it causes serious damage, and propose a targeted fix: local additional insulation, resealing a joint, or adding a missing detail as part of a full insulation job.
A thermographic inspection is also non-destructive and fast. A drone flies around the building within an hour and provides a complete overview of the thermal behaviour of the whole envelope - no scaffolding, no drilling into walls, no need to enter individual flats.
Do you want to know exactly where in your house or apartment building heat is escaping? We offer drone-based thermographic inspection of buildings that reliably reveals and precisely locates thermal bridges. Based on the results you receive a clear report with photo documentation and recommendations on what to fix and where. Request an inspection today - we reply within 24 hours.