Insulation R-Value Defined

Insulation R-Value Defined

Energy efficiency has become an increasing concern in the Real Estate and Property Insurance Industries. The performance of the insulation products installed in a building or dwelling are important factors to be considered when building, purchasing, or renovating a home or commercial property.

As Industry Professionals, it is helpful to be familiar with methods used when determining the R-Value of insulation materials.


R-Value Defined

RValue is defined as “The measurement used when quantifying the level of a specific material’s thermal resistance”.

How Does R-Value Relate to Insulation?

The function of insulation is to provide resistance to the flow of heat, and R-Value is the measure a material’s resistance to this heat flow.

A high R-value equates to higher resistance to heat flow. An insulation material’s R- Value, in conjunction with where and how it is installed, determines its overall effectiveness.

Quick Fact

Heating and cooling costs for a typical home in the US account for approximately 65% of the home’s total monthly energy usage.

Factors to Consider Regarding Thermal Resistance

When considering R-value as a means to determine the thermal resistance of a building component, there are other factors that must also be taken into account. While R-values are an excellent guide for comparing the attributes of different insulation products, they apply only when the insulation is properly installed.

• For example, if two layers of insulation are compacted and forced into the space intended for only one layer, the R-value does not double.

• Likewise, if a single layer of insulation is compressed during installation, it will not be as effective. Stuffing “batt”-type insulation sized for 5 inches into a 4-inch wall cavity will actually lower its R-value!

• Ensuring that insulation is correctly installed will help allow the product’s full benefits to be realized.

Calculating and Converting R-Value

The equation used to calculate R-value can be helpful not only to Industry Professionals, but it can be helpful to Homeowners as well.

If the R-Value of the insulation is known, the following equation can be used to help calculate heat loss. The equation for determining R-value is as follows: R-Value = Temperature Difference x Area x Time

Heat Loss

  • The Temperature Difference is expressed as T (“Delta T”) and is measured in degrees Fahrenheit (Deg F)
  • The Area is expressed as A and is measured in Square Feet (Sq Ft)
  • The Time is expressed as T and is measured in Hours (H) The Heat Loss is expressed as L and is measured in British Thermal Units (BTU)
  • R-Value = T x A x T / L

Current Regulations Regarding R-Value

In the 1970s, the Federal Trade Commission (FTC) created a rule requiring insulation manufacturers to disclose the R-Value of insulation material. This was intended to protect purchasers from false manufacturer claims, as well as to create a standard by which insulation products could be compared. The U.S. Department of Energy (DOE) regularly issues recommendations for insulation R-values in new and existing homes. The recommendations are based on a comparison of the cost for installing insulation versus potential future energy savings.

Quick Fact

The DOE R-Value recommendations for attics, cathedral ceilings, walls and floors are generally greater than what is actually required by most current building codes.

R-Value Thickness Comparison Matrix

Below is a simple matrix that can useful in determining the R-Value of a material as compared to its thickness:

Knowledge of R-value ratings can be useful, especially when comparing the effectiveness of insulation products, but understanding a bit about how other factors affect a building component’s thermal resistance is important if insulation is to be used to its full benefit. Industry Professionals who are familiar with the basics of insulation R- values can provide “value-added” to their clients should questions regarding a property’s energy efficiency arise.

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