When checking insulation spec sheets, the R-value comes up quite often. What is R-Value? We’ll look at what the R-value means, how it’s calculated, what are the minimum recommended values of R for attic, 2×4 and 2×6 walls, and so on (you’ll find Complete Insulation R-Value Chart further), and what is so important to choose building materials with high R-values.
What is Insulation R-Value?
The R-value of a building material is Resistance for the flow of heat. Known R-value a thermal resistance, R stands for resistance, It is a numerical expression of how good some building material is an insulator.
The higher the R-value of a material, the better it is an insulator.
Example: R-30 material is 3 times better insulator than R-10 material. This is why it is recommended to use great insulation materials for attic (minimum recommended R-value is R-30), ductwork (R-42). For example, walls are not the best insulators; They should usually have an R-value higher than R-11.
Here are some estimates to illustrate how important good insulation (high R-value content) really is:
- poorly insulated buildings The heat loss (winter) and heat gain (heat) experienced will be the same as 50%, Example: The monthly heating bill could be $100 but you’re paying a $200 heating bill because of poor insulation.
- About this 30% Loss of heat loss/gain comes from poorly insulated Roof (significance of the higher R-value range) and approx. 70% heat loss/gain is experienced walls, glass windows, and so on (the importance of good R-values for walls, for example).
- As much as 90% of ceiling heat loss/gain can be prevented with high R-value roofing material, We also see 60% less heat loss/gain through walls with higher R-values.
With all this in mind, let us first look at how the R-value is defined. After that, we’ll look at the R-value charts for the different materials. Based on that, you can choose the highest R-value material to insulate your home.
What does the R-value mean in insulation?
R-Value – Thermal Resistance – Basically how do you put ‘what a good insulator’ Any material is in number. What does ASHRAE actually measure? (A lot of research has been done on this in the 50s and 60s) thermal conductivity or k-value,
k-value is the measure of heat that flows through 1 square foot material with 1 inch thickness In 1 Hour For each degree of temperature difference Between indoor/outdoor temperatures.
We can calculate the R-value from the K-value using this simple equation:
R-Value = 1 / K-Value
Basically, the R-value is the inverse of the k-value. The k-value (thermal conductivity) is measured, and then the R-value (thermal resistance) is calculated from the k-value.
Let’s look at an example for Wood’s R-values to see how R-values are calculated:
Example: What is the R-value of wood?
ASHRAE measured the k-value of both softwood and hardwood. They determined that a total of 0.71 BTU is lost through 1 inch of 1 square foot of softwood in 1 hour. This means that the k-value for softwood is 0.71. For hardwood, the k-value is 1.41.
Based on this k-value, the R-value for the wood is calculated. According to the US Department of Energy (source here, “The R-value for lumber ranges between 1.41 per inch for most softwoods and 0.71 for most hardwoods”,
This means that a 6-inch softwood has an R-rating of 6×1.41 = 8.46. Basically we can say that 6 inches The R-value of softwood is R-8 . It happens, and a 6-inch hardwood has an R-value of R-4.
You can read more about how ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) Here the k-value measures,
ASHRAE also calculates R-values from measured k-values, and publishes the results known as ‘R-value chart’,
Here is a comprehensive chart that includes the various R-ratings for building materials:
Insulation R-Value Chart
|Construction material:||R-Value (1 Inch Thickness)||R-Value (5 inch thickness)||R-Value (10 Inch Thickness)|
|closed cell spray foam||7.00 R-Value||35.0||70.0|
|open cell spray foam||3.80 R-Value||19.0||38.0|
|foam board||4.00 R-Value||20.0||40.0|
|gypsum or plaster board||0.9 R-Value||4.5||9.0|
|wood panels||1.25 R-Value||6.25||12.5|
|wood-fiber board||2.38 R-Value||11.9||23.8|
|wood-fiber hardboard||1.39 R-Value||6.95||13.9|
|fir wood||1.25 R-Value||6.25||12.5|
|asphalt tile||0.32 R-Value||1.6||3.2|
|ceramic tile||0.08 R-Value||0.4||0.8|
|cork tile||2.22 R-Value||11.1||22.2|
|plywood subfloor||1.25 R-Value||6.25||12.5|
|rubber tile||0.20 R-Value||1.0||2.0|
|plastic tile||0.20 R-Value||1.0||2.0|
|wood subfloor||1.25 R-Value||6.25||12.5|
|cotton fiber||3.85 R-Value||19.25||38.5|
|mineral wool||3.70 R-Value||18.5||37.0|
|wood fiber||4.00 R-Value||20.0||40.0|
|fiber glass||4.00 R-Value||20.0||40.0|
|roof deck slab||4.17 R-Value||20.85||41.7|
|cellular glass||2.50 R-Value||12.5||25.0|
|Cork board||3.7 R-Value||18.5||37.0|
|hog hair||3.00 R-Value||15.0||30.0|
|plastic (foamed)||3.45 R-Value||17.25||34.5|
|shredded wood||1.82 R-Value||9.1||18.2|
|macerated paper||3.57 R-Value||17.85||35.7|
|sawdust or shavings||2.22 R-Value||11.1||22.2|
|roof insulation||2.78 R-Value||13.95||27.8|
|brick (common)||0.2 R-Value||1.0||2.0|
Source: Courtesy of ASHRAE 1960 Guide
You can use this table to get an idea of what the R-value means in insulation for various building materials.
Example: What is the R-Value of Spray Foam Insulation? Well, we differentiate between closed cell and open cell spray foam insulation. Closed cell foam has a high R-7 insulation value and open cell foam has a substantial R-3.8 insulation value.
What R-Value Insulation Do I Need? (attic, walls, etc.)
Insulation is almost always a smart investment. You want as high an R-value material as possible.
Depending on where you live in the US, there are different minimum recommendations for rooms/spaces that need to be well insulated. They give you an idea of what r-value you need.
Energy Star did a good analysis of exactly what R-value insulation you need for attics, 2×4 walls, 2×6 walls, floors, and crawl spaces.
First, you need to check what insulation climate zone you live in (there are 8 of them; South Florida is 1, North America is 7, etc.). you should Check Your Area on Energy Star Here And come back for the R-value recommendations.
What’s the R-value for Attic Insulation?
For attic insulation, you will need a minimum R-30 value of insulation.
- Zones 1 and 2: R-30 to R-49 are recommended.
- Zone 3: R-30 to R-60 is recommended.
- Zones 4 and 5: R-38 to R-60 are recommended.
- Zones 6 and 7: R-49 to R-60 are recommended.
Sometimes you ask ‘Is R-19 insulation good for the attic?’ See questions like? or ‘Is R-30 insulation good for the attic?’. R-30 is the recommended minimum, yes, but R-19 is insufficient for an attic.
What size insulation for 2×4 walls?
For 2×4 walls, the minimum recommended R-value of insulation is R-13. For all regions across the United States, it is recommended to have R-13 to R-15 insulation for 2×4 walls.
What size insulation for 2×6 walls?
For 2×6 walls, the minimum recommended R-value of insulation is R-19. For all regions throughout the United States, it is recommended to have R-19 to R-21 insulation for 2×6 walls.
What size insulation for floors?
Floors require a minimum of R-13 insulation. The further north you go, the higher the minimum recommendation for floor insulation:
- Zones 1 and 2: R-13 floor insulation is recommended.
- Zone 3: A minimum floor insulation of R-25 is recommended.
- Zones 4, 5, 6 and 7: R-25 to R-30 floor insulation is recommended.
What size insulation for a crawl space?
At least R-13 insulation is recommended for crawl spaces. Same story here; The further north you go, the more insulation you’ll need:
- Zone 1: R-13 insulation is sufficient for the crawl space.
- Zone 2: R-13 to R-19 crawl space insulation is recommended.
- Zone 3: R-19 to R-25 insulation is recommended for crawl spaces
- Zones 4,5,6 and 7: R-25 to R-30 minimum R-value insulation is recommended for crawl space.
Hopefully, now you have a better understanding of what R-value means. We’ve covered different R-values for different materials and you can check out the minimum recommended values of R insulation for spaces that need to be insulated the most.