What is Insulation R-Value? (+ Insulation R-Value Chart)

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.

what is the insulation r value for attic
Using mineral wool to insulate an attic. The attic requires at least R-30 insulation and a 1-inch mineral wool has an R-3.7 value. This means that 10 inches of mineral wool would have an R-37 R-value.

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
plywood 1.25 R-Value 6.25 12.5
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
softwood 1.41 R-Value 7.05 14.1
hardwood 0.71 R-Value 3.55 7.1
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
linoleum 0.56 R-Value 2.8 5.6
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
terrazzo 0.98 R-Value 4.9 9.8
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
vermiculite 2.08 R-Value 10.4 20.8
roof insulation 2.78 R-Value 13.95 27.8
Solid 0.19-1.42 R-Value 0.95-7.1 1.9-14.2
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.


Leave a Comment