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What is R-Value in Insulation?

Tuesday, May 1st


If you're looking to improve the energy efficiency of your home and upgrade the insulation in the attic, then you've probably come upon the term “R-value.” R-value is a way to measure and understand the effective insulating value of a specific material and is useful when comparing different insulation types.

In this post, we’ll explore what R-value is and even go over the R-value of many common insulation materials.

What is R-Value?

The R-Value of a material is the measure of how resistant it is to heat transfer. This is also sometimes known as the material’s thermal resistance.

The higher the R-value the more resistant the material is to heat transfer for any given thickness. The more resistant, the longer it takes for heat to flow out of the room through the material, and as a result, less energy is required to keep a room at a given temperature.

You can think about it like a large winter coat. Winter coats do not actually make you warmer on their own, but rather they trap the body heat that you produce and make it harder for it to escape. Since temperature is always seeking equilibrium, your body heat will simply disperse into the cold air without this additional obstacle. 

How is R-Value Calculated

To calculate the R-Value of a material you can use the following formula: R-Value= (Temperature Difference x Area x Time) / Heat Loss.

R-Value formula calculation
Let’s break that down:

  • Temperature difference: The difference in temperature in degrees Fahrenheit between the outside and the interior room
  • Area: The square footage of the room (4 walls, ceiling, and floor) that stands between the inside and the outside
  • Time: Time elapsed in hours
  • Heat loss: Heat loss, expressed in BTUs

R-value is usually expressed on a "per inch" basis. Using this formula on your own gets complicated quickly. The real usefulness of the R-value is to identify a goal for your home and to compare insulation types.

Thicker insulation generally increases R-value proportionally. Insulation can lose its insulating properties, such as when fiberglass insulation gets wet. In addition, cracks and gaps in a home can lessen the effectiveness of your insulation: it doesn’t matter how high your insulation’s R-value is if cold air simply sneaks in through the cracks.

The other major factor to consider when choosing insulation is the environment. The colder your climate, the more insulation you’ll need. The map below shows the climate zones of the United States and the chart displays the recommended amount of insulation for homes in each region (source: Energystar.gov).

Map of Climate Zones and R-Value Chart by Zone

Recommended Insulation Map of US

For example, if you live in Kentucky, you live in Zone Four (the yellow area of the map). Looking at the chart below the map, you would locate Zone 4, then consult the three columns for the recommended R-value you should add. Note that the three columns break out the recommendations for uninsulated attics, attics that already have some insulation, and for uninsulated basements or crawl spaces. So, if you have some insulation in your Zone 4 home, you would want to ADD insulation with R38 value.

Every dealer in the Dr. Energy Saver network is trained in home energy assessments and can help determine the levels of insulation that would achieve optimal energy efficiency in your home.

Contact your local Dr. Energy Saver dealer today to schedule your estimate.

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