R-Values

Insulation Values And Methods

What is an R-value?

Thermal resistance ratings or R-values are predominantly used in the building industry to determine the insulation properties of certain building materials. Its use is limited to situations where thermal insulation is achieved by retarding the flow of heat through the material itself rather than reflecting radiant heat away. The higher the R-value, the greater the insulation.

R-value is a measure of apparent thermal conductivity, and it thus describes the rate at which that heat energy is transferred through a material or assembly, regardless of its original source.

Although R-Values offer a useful means of comparing the performance of different products, other factors need to be considered in maintaining thermal comfort.

What is Thermal Mass?

“Thermal Mass” is the capacity of a material to store heat energy.

Materials such as concrete have poor thermal resistance (R-value typically less than 1) but work well for thermal mass applications (e.g. passive heating and cooling) because of their high specific heat. Such materials can slowly store or release, relatively large quantities of heat compared to other materials.

In building terms, it reduces temperature fluctuations by absorbing heat when the ambient temperature is hotter than the mass, and then releasing the heat when the ambient temperature falls below the temperature of the mass.

Thermal mass should not be confused with insulation. Materials used for insulation typically have much lower thermal conductivity than materials used for thermal mass and generally do not have a high capacity to store heat. They can reduce unwanted heat transfer but are not significant sources of heat in themselves. Often a combination of good insulation and thermal mass is used to achieve an optimum solution.

What is a Thermal Bridge?

Thermal bridges, also known as cold bridges, are areas in a building envelope that have a higher heat transfer rate compared to the surrounding areas.

A thermal bridge is created when materials that are poor insulators come in contact or penetrate through a good insulation barrier, allowing heat to flow through the path created. They typically occur at points where different building components are joined, such as window and door frames, wall-roof junctions, and other building penetrations.

Insulation around a bridge is of little help in preventing heat loss or gain. Surface moisture due to condensation can also occur on the surface where the thermal bridge occurs.

EPS (Expanded Polystyrene) is a thermal break. When used as wall cladding, it will insulate the walls, trapping the exterior air temperature out and the inside air temperature inside the house. This will, in turn, make the framing far more stable as it doesn’t have to endure constant temperature fluctuations, reducing the potential for movement in the wall structure.

Examples of thermal bridging

• Concrete balconies that extend the floor slab through the building envelope
  
• Nails that are used to fix insulated wall cladding
  
• Timber/Metal battens that are used to separate insulated wall cladding
  
• Timber framing used to construct a house
  
• Single glazed windows
  
• Certain types of aluminium joinery