Insulation: What is R-Value?

May 25th, 2021

R-value is the measure of how well a layer of insulation reduces the rate of heat flow. The higher the number, ranging from 1.5 to 7, the more effective the insulation batt is at increasing thermal efficiency. 

Thermal Resistance is the most important material characteristic when specifying insulation. There are two factors affecting the thermal resistance: the thickness of the insulation and the thermal conductivity of the material. It can be calculated through the formula (R-Value = Thickness (m) / Thermal conductivity (W/mK).

Temperature and moisture levels can affect the R-value, which is why it is so important to regulate heat and moisture in the home. Oven mitts have a good R-value because heat moves through them slowly, however if you get them wet it transfers heat too quickly and their R-value drops. The same idea applies the heat and moisture in the home! 

There are three kinds of R values that are used to more specifically measure heat flow resistance variables:

The Down R Value (Summer R Value): Measures the insulation’s ability to resist heat flow from entering.

The Up R Value (Winter R Value): Measures the insulation’s ability to resist heat flow from escaping.

The Total R Value (Most Common): The combination of the up and down R values. 

Image Source: Building Code of Australia (https://build.com.au/bca-requirements-insulation)

The Building Code of Australia provides energy efficiency provisions for new homes. Regions are broken up into zones that require a different  minimum R-value depending on the particular climate in that area. For example, a home in a hot area would only need an R value of 3 or 4, whereas a home in a colder climate would need a minimum of 5 or 6. Using a thicker product is more economically efficient than using a product with a lower thermal conductivity when you are trying to achieve a specific thermal resistance. 

While it can sound quite technical, if you have understood the concepts in this blog you will have a great understanding of the role R-Value plays in selecting the right insulation for your next build!

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