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Understanding Thermal Ghosting and How to Combat It


Thermal ghosting is a phenomenon that occurs in homes or buildings where thermal bridging has taken place. Thermal bridging is a condition where heat is transferred through a wall or ceiling, creating cold spots that can lead to harmful consequences. 

These cold spots are often visible as dark, ghost-like patterns on walls or ceilings, giving rise to the term “thermal ghosting.” 

This article explores thermal ghosting in depth and provides some tips on how to combat it.

What Causes Thermal Ghosting?

Thermal ghosting occurs when heat is transferred through a building envelope, which is the interface between the interior and exterior of a building. This can happen in several ways, but the most common cause is thermal bridging. 

When the inside and exterior of a building are connected by a material with high thermal conductivity, such as metal or concrete, thermal bridging takes place. This allows heat to flow through the material, creating cold spots on the surface of the wall or ceiling. 

These cold spots can then attract moisture, which can cause mould growth and other problems.

When a building’s inside and exterior are at different temperatures, thermal ghosting can also happen. This can occur when a room is heated and the walls or ceiling are not properly insulated. 

The heat will escape through the walls or ceiling, creating cold spots where moisture can accumulate.

How to Combat Thermal Ghosting

There are several ways to combat thermal ghosting, depending on the cause. The first step is to identify the cause of the problem. 

This can be done by inspecting the walls or ceiling for signs of condensation or mould growth. If there is condensation or mould growth, it is likely that thermal bridging is the cause.

Insulating the Walls and Ceiling

An effective way to combat thermal bridging is to insulate the walls and ceiling. This involves adding insulation to the walls and ceiling to prevent heat from escaping. 

Insulation comes in various forms, including fibreglass, cellulose, and spray foam. 

  • Fibreglass insulation is the most commonly used type of insulation, but it can be difficult to install in walls and ceilings. 
  • Cellulose insulation is easier to install and provides better insulation, but it can be more expensive. 
  • Although spray foam insulation is the most efficient, it is also the most expensive.

Using a Vapor Barrier

A layer of material known as a vapour barrier keeps moisture from penetrating the ceiling or walls. This can be particularly effective in preventing mould growth and other problems associated with moisture. 

The vapour barrier should be installed on the warm side of the wall or ceiling to prevent moisture from entering.

Installing a Thermal Break

A thermal break is a layer of material that is inserted between the interior and exterior of a building to prevent heat from flowing through. This can be particularly effective in preventing thermal bridging. 

Foam, rubber, and fibreglass are just a few of the materials that can be used to create a thermal break.

Using an Air Barrier

An air barrier is a layer of material that prevents air from flowing through the walls or ceiling. This can be particularly effective in preventing thermal bridging, as air can carry heat and moisture through the walls or ceiling. 

Plastic, foam, and rubber are a few of the materials that can be used to create an air barrier.


Being aware of thermal ghosting and taking measures to combat it is crucial for maintaining a healthy and sustainable living space. By addressing the underlying causes of thermal bridging, you can prevent thermal ghosting and other problems, such as mould growth and energy inefficiency.

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