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 |

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.

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