R-Value Insulation | What R Value do I need - Attic Projects

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License #1035247

CALL NOW! San Diego: 858-246-7421 or Orange County/Los Angeles: 714-769-0228

What R-Value Insulation Do I Need?

R-values for insulation often appear on specification sheets and measure how well the material resists heat flow. As the R-value increases, so does the insulation per inch of thickness.

Many homeowners ask, “What R-value do I need?” This article will discuss what R-Value means, how to calculate the R-value, and how R-value affects your home’s insulation. 

What Is R-value?

R-value refers to thermal resistance, with the “R” standing for “resistance.” R-values for insulation represent the insulating capacity of a certain material. Insulation with a higher R-value will provide a more comfortable living space and save energy costs.

What Does R-value Mean in Insulation?

The R-value measures how well a material insulates in numbers. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) has created a means to measure thermal conductivity, or k-value, using research dating back to the 1950s.

K-value measures the amount of heat that flows through one square foot of material with one-inch thickness in one hour. The k-value can help calculate the required insulation R-value, R-value for roof insulation, and ceiling insulation R-value.

To calculate the R-value from the k-value, we can use the equation: R-value = 1/k-value.

By measuring a material’s k-value (thermal conductivity), we can calculate the R-value (thermal resistance). R-value acts as the inverse of the k-value, so the lower the k-value, the better the insulation. Let’s examine the calculation of R-values by using wood as an example.

As part of an ASHRAE study, experts measured the k-values of softwood and hardwood. Based on those k-values, the U.S. Department of Energy reported that softwoods have an R-value of 1.41 per inch while hardwoods have an R-value of 0.71.

Using this data, we can answer the question, “What R-value do I need?” The R-value for five inches of softwood equals 5 x 1.41 = 7.05. In other words, five inches of softwood requires an R-value of 7 and five inches of hardwood an R-value of 3.5.

R-Value Insulation Chart

The chart below contains the R-values for different building materials. For example, closed-cell spray foam has a higher R-7 insulation value, while open-cell foam has an R-3.8 value.

Building Material R-Value (One Inch Thickness) R-Value (Five Inches Thickness) R-Value (Ten Inches 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
Pine 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
Glass Fiber 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
Corkboard 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
Concrete 0.19-1.42 R-Value 0.95-7.1 1.9-14.2
Brick (Common) 0.2 R-Value 1.0 2.0


What R-value Insulation Do I Need?

Investing in insulation will eventually pay off, so you want to select materials with a high R-value. The recommended insulation level for rooms and spaces depends on where you live. Use the insulation chart or consult a professional to determine what R-value you need.

Before starting, you must find out which insulation climate zone you live in. Energy Star has created recommended R-values based on seven zones. Additionally, Energy Star performed an analysis to determine what R-value insulation you need for your walls, attic, floor, and crawlspace. 

R-value for Attics

Match your climate zone to the recommended R-value below. For example, if you live in zone four, consider getting insulation with an R-value between 38 and 60. The R-value for roof insulation and attic insulation should have a minimum value of 30.

  • Zone One and Two: R-30 to R-49 
  • Zone Three: R-30 to R-60
  • Zone Four and Five: R-38 to R-60
  • Zone Six and Seven: R-49 to R-60 

R-value for Walls

2×4 walls require a minimum wall insulation R-value of 13, so select insulation with an R-value of 13 to 15. For 2×6 walls, you need an R-value of 19, and the recommended wall insulation R-value for all zones falls between 19 to 21. If you decide to insulate the ceilings, they should have a minimum ceiling insulation R-value of 30.   

Frequently Asked Questions 

Is a Higher R-value Better for Insulation?

The R-value denotes the effectiveness of the insulation, so choose insulation materials with the highest R-value possible. A higher R-value means better insulation performance, especially if you live in colder areas. 

Which Insulation Has the Best R-value?

Closed-cell spray foam has the best R-value of 7 per inch. Spray foam also has exceptionally high density, making it one of the most effective types of insulation. 

Does Doubling Insulation Double R-value?

Doubling insulation does double R-value. Due to the law of diminishing returns, doubling insulation from R-10 to R-20 will reduce energy consumption more than doubling R-20 to R-40. Attics usually have plenty of space for doubling insulation.


Attic Projects provides one-stop insulation services. Our team uses high-quality materials that will insulate and protect your home for years to come. We can handle spray foam insulation, attic insulation upgrades and removals, loose-fill or blown-in systems, batt insulation, and vapor barriers.

If you need more information on “What R-value do I need?” contact Attic Projects today to get a free quote and insulation consultation. Call us at (858) 282-0516.