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What is R-Value? Fully Explained

what is r value

The R-Value is a measure of insulation for your home

This blog post discusses the importance of insulation, what it does to keep you warm in winter and cool in summer, and how to calculate the R-value for your home.

So, what is R-value?

R-value is the measure of thermal resistance to heat flow. The higher the R-value, the greater the insulating power of a material or an assembly between you and the outside temperature. 

It’s often mistakenly called “resistance” or insulation value by consumers and professionals in construction trades.

But it’s not about “resistance,” it’s about moving heat from the inside of a house to the outside. 

And it’s not about stopping air infiltration, as some think; it’s about minimizing air convection—the movement of warm air toward cool areas and vice versa. 

And it’s material-specific, depending on its thickness and other specs you can find on a product label or manufacturer website.

Why is it important?

Well, if you live in a climate where the temperature is around 50°F for four months and then plummets to -20° during the other eight months of winter, as many Americans do, you want a home that’s well-insulated.

R-value may be an accurate measure of how well your house insulates you from the temperature extremes. 

If you live in a milder climate, where average winter lows stay near freezing and high summertime temperatures reach only 80°F, R-value will be less important to your home’s insulation power.

How does it work?

Heat always moves from a high temperature to a lower one, when there’s a difference in temperature. That is, heat goes down. 

This process is called “convection.” When you have cold air blowing out of your heater register in the wintertime, that’s convection at work.

R-value measures how well your home resists this movement of heat. The higher the R-value, the less your house lets warm air seep or flow out into cold areas. 

This means that common living spaces stay at a more comfortable temperature throughout the winter.

Insulation is used to reduce the transfer of heat (or cold) through conduction, convection and radiation. 

There are three types of heat transfers that all affect how warm or cool you feel, depending on the surrounding temperature.

There are three types of heat transfer:

  • Conduction: This is the direct transfer of heat from one molecule to another. Imagine a burning candle used for decoration inside your home.
    • The flame is giving off heat, which heats up surrounding molecules of oxygen and wood, eventually catching fire.
    • This type of heat transfer is also known as a conductive heat transfer.
  • Convection: Heat transfer from the movement of liquids or gases. Imagine taking a hot shower, or washing your hands in hot water.
    • The water is being heated by the water heater and transferring its heat to you, making you feel warm.
    • This type of heat transfer is also known as a convective heat transfer.
  • Radiation: This is the direct transfer of heat through empty space.
    • On a sunny day, you can feel the rays of sunshine heating up your skin.
    • This type of heat transfer occurs in both natural and artificial lighting. Radiation is also known as radiant heat transfer.

How to calculate the R value?

First, determine what type of insulation you would like to install in your home. 

Some common types include foam board insulation, fiberglass insulation, and cellulose insulation. 

Different types of insulation have different R-values. The higher the number, the better it is at insulating your home.

R-value is a unit used for measuring insulation, and it’s determined by multiplying the thickness of an insulator by its resistance to heat flow. 

The higher the number, the better the insulation quality.

  • Square Feet: Multiply R-value by the insulation thickness.
    • The resulting number is the square footage of insulation being used.
    • For example, if you have 6 inches of fiberglass insulation in your attic, with an R-value of 12.2, then multiply 6 x 12.2 = 72.8 square feet or 100 square yards of insulation
  • Square Meters: Multiply R-value by the insulation thickness.
    • The resulting number is the square meter amount of insulation being used.
    • For example, if you have 20 mm (20 millimeters = 0.2 m) of polyurethane foam insulation in your attic, with an R-value of 3.14, then multiply 0.2 x 3.14 = 0.6 square meter or 6 square feet of insulation
  • Room Volume: Multiply R-value by the thickness.
    • The resulting number is how much R-value you are adding to your room, in millimeters (or inches).
    • For example, if you have 7 mm of polyurethane foam insulation on your attic floor, with an R-value of 3.14, then you are adding 21 square meters or 42 square feet or 1/2 inch of insulation.

Common types of insulation

  • Fiberglass – The most common type of insulation, fiberglass is made from glass fibers that are spun together to make a thin bat.
    • The bat can be sprayed or blown into attics and walls during construction
  • Cellulose – This type of home insulation absorbs moisture easily, which makes it perfect for locations with high humidity levels like bathrooms and basements.
    • It’s treated with borates to prevent mold and insect infestations.
  • Foam – This type of insulation is made from a variety of chemicals, including water, air or foam.
    • This can be sprayed as a liquid into wall cavities before the studs are installed.
    • It expands when it comes in contact with heat, which helps keep homes energy efficient.

How do I get it?

You can get insulation with high R-value in all types of insulation products for walls, floors, and ceilings. 

The most versatile type of insulation is mineral fiber insulation products, which can be made to any thickness, are cost-effective, provide high R-value at many thicknesses, are easy to handle and install–and they’re also effective at blocking air infiltration.

Conclusion

In conclusion, R-value is a measurement of thermal resistance used to determine the heat loss from one side of an object to another. 

The higher the number means that there will be more insulation and less heat loss. 

This information can help you make better decisions on what materials should be included in your home or building for energy efficiency purposes.