How Is R-Value Calculated?



As you take on your next major project, you’ll want to know that the insulation you’re using is the best fit for the job. One of the most effective strategies for measuring an insulation’s overall performance is to calculate its R-value. 

R-value is a rating system that grades the effectiveness of insulation products based on their composition. The “R” in “R-value” refers to a material’s resistance to heat flow. The greater the R-value, the greater the resistance and the higher insulation performance for all spaces: commercial, industrial, and residential. In the long term, understanding R-value and purchasing the right insulation can improve your energy efficiency and reduce overhead costs. 

But how exactly is R-value calculated? We’ll take a look below at the formula, variables to be aware of, and the insulation options for you to choose from based on their associated R-values. 


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How Do You Determine R-Value?

In order to calculate the R-value of a particular piece of insulation, you divide the thickness of the material by its thermal conductivity. Thermal conductivity measures the rate at which temperatures transmit through an insulating material. 

Some materials are multilayered. To calculate the R-value of a multilayered material, simply add the R-values of each of the individual layers together. Usually, the more insulation you install, the more R-value and resistance to heat flow increase. 

Use the following equation to calculate the R-value for your insulation project

R−Value = ΔT×Area×Time / Heat Loss

  • ΔT = the temperature difference inside and outside the industrial/commercial space
  • Area = the area that's being insulated (ft 2)
  • Time = how long the measurement took place (seconds)
  • Heat Loss = how much heat is lost through a surface, ceiling, or wall

Additional R-Value Factors to Consider

There are three key variables to take into account when determining the R-value of a given material: temperature,density, and moisture. It is also important to consider the location in a residence, commercial building or industrial facility where the insulation project will take place, especially those that require high thermal stability. For example, the R-value of an insulation material installed in a wall will differ from that of the same insulation installed in a ceiling because of the change in heat flow through wall joists, studs, and so on. 

On a larger scale, an insulation material’s R-value will also fluctuate based on the local climate of the project and the types of heating and cooling systems available at the job site. 

Installation Effectiveness 

Some types of insulation are naturally more effective than others. Based on their respective R-values, the following insulation types are rated from lowest to highest R-value per inch:

  • Blown-in (or loose-fill) insulation
  • Insulation blankets (batts and rolls)
  • Spray foam insulation
  • Foam board insulation 

It is important to note that radiant barriers and vapor barriers are not rated by R-values

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Insulation R-Value Requirements

Aside from their intrinsic benefits, insulation materials must also abide by a set of criteria, which varies from state to state. Especially in the case of low-slope commercial roofing, project managers must consider insulation requirements and code-compliant assembly. Typical R-value requirements in California, Colorado, and New Hampshire, for example, fall around the R-30 range. Some states have an R-value requirement as low as R-20, which is the case in Mississippi and Alabama, or as high as R-40 in places like Vermont and Alaska. Of course, as previously stated, local climate is an important consideration. 

For more information about local code requirements in your area, you should consult with your local jurisdiction. You can also read up on The International Energy Conservation Code (IECC) for the latest industry standards. 

Choosing the right insulation for your next project can feel like an arduous task. But selecting from a variety of insulation options doesn’t have to be exhausting. Distribution International has a robust inventory of insulation materials for your next commercial, industrial or residential project, all of which can be purchased through the CustomerConnect portal. If you have specific questions about your project, don’t hesitate to contact our world-class customer support center

To learn more about viewing and managing your insulation quotes and orders without the extra hassle, register for CustomerConnect today

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