Cellulose Insulation R-value (of Loose, Wet Spray & Dense)

R-value is an essential factor to consider regarding how well your home will stay warm in the winter and cool in the summer. Cellulose is one of the most common forms of insulation worldwide. How much heat loss can it prevent, what is the R-value of cellulose insulation?

Cellulose insulation R-value

Cellulose insulation has a higher R-value than many other insulation materials, making it an excellent choice for heat resistance. The R-value of cellulose varies from 3.5 to 4.0 depending on the type of cellulose and the brand’s quality. Three main types of cellulose have the following R-value range:

Cellulose insulation typeR-value (per inch of thickness)
Loose-filled3.5 (approximately)
Wet spray3.6 to 3.8
Dense-packed3.8 to 4.0
Cellulose insulation R values

What is R-value?

An R-value or thermal resistance measures a material’s ability to resist heat flow. The higher the R-value, the more effective the material is at insulating.

R-values for varying thicknesses of cellulose

The R-value of cellulose insulation varies with how thick the insulation is laid. Thicker insulation offers more heat resistance and hence a larger r-value.

Loose cellulose insulation
Loose cellulose insulation

Loose-filled cellulose insulation provides an R-value of approximately 3.5 per inch, so a 2-inch thickness of cellulose insulation will achieve an R-value of 7. 


  • 4-inch cellulose insulation has an R-value of 14.
  • 6-inch cellulose insulation has an R-value of 21.
  • 8-inch cellulose insulation has an R-value of 28.
  • 10-inch cellulose insulation has an R-value of 35.
  • 12-inch cellulose insulation has an R-value of 42.

For a quick look, here is a cellulose insulation R-value chart for different thicknesses:

Thickness (in inches)R-value
1 inch3.5
2 inch7
4 inch14
6 inch21
8 inch28
10 inch35
12 inch42

Cellulose R-value compared to other insulating materials

When insulating your home, you want to ensure you use the best possible material. Spray foam insulation is hands down the best insulating material with a high R-value, but it can be more expensive than other home insulation materials. On the other hand, Cellulose is cheaper than spray foam insulation and has an excellent R-value, making it a perfect option for many home insulation projects.

This R-value comparison table will help you decide which insulation suits your home’s insulation needs better.

Name of Insulation MaterialR-value
Cellulose3.2 to 3.8 (depending on loose-fill, dense-packed, or we-spray)
Spray Foam (closed-cell)R-7
Foam board3.6 to 8 (based on the type of foam board)
Rockwool3 to 3.3 (depending on manufacturing quality)
Fiberglass2.2 – 4.3 (varies for blown-in, loose-fill, or batts)
Different insulation materials and their corresponding R-values

Advantages and disadvantages of cellulose insulation

Cellulose is an excellent choice if you’re looking for eco-friendly, cost-effective, and energy-efficient insulation. It’s made from recycled newspapers, so it’s a sustainable option. Plus, it’s fire resistant, heat resistant, and has a high R-value, so it will keep your home comfortable efficiently. It is also treated for being mold resistant, so you won’t have to worry about any health hazards.

However, cellulose has its fair share of disadvantages as well. I will recommend reading this article for detailed pros and cons of cellulose insulation. Also, cover the wall plates and floor intersection.

How is cellulose insulation installed in homes?

Choosing a high-quality insulation material is useless if it is not installed properly. The effectiveness of cellulose in insulating your home depends upon its correct installation. Follow these steps for installing loose-fill cellulose insulation:

  • The first step of cellulose installation is air sealing. You will need a simple caulk gun and a spray bottle with insulating foam to seal holes and gaps in areas where cellulose insulation is being applied.
  • Then seal the areas around pipes, wires, fan housing, lights, and junction boxes.
  • Once you have sealed all potential leak points, install the cellulose into the open attic or enclosed wall. You will require a blowing machine for installing cellulose. You can easily rent this machine from companies offering insulation services.

Cellulose installation is a labor-intensive process, so hiring a professional insulation company is recommended to apply the insulation correctly. It will ensure that there are no problems with your insulation later on and it performs its purpose efficiently.

Does cellulose insulation lose R-value?

Cellulose insulation naturally sags and settles over time which can decrease its R-value. Settling results in aeration within the material that may reduce the R-value of the insulation by 15% to 20%. Additionally, moisture, pests, or other factors can speed up settling and contribute to the loss of R-value. To offset this settling and maintain the R-value, contractors usually install 15-20% more insulation. 

For example, in colder climates, the attic insulation should have a thickness of 16 inches. To account for settling, the contractor will install 16 inches plus additional 3.2 inches (20% more) of insulation. So, the attic will get a total of 19.2-inch thick cellulose insulation.

Is fiberglass insulation better than cellulose?

Fiberglass insulation is often considered the better option for insulating your home. However, cellulose insulation actually has a higher R-value, meaning it is better at insulating against heat loss. cellulose is also fire resistant and does not off-gas as fiberglass insulation can. However, fiberglass can lose R-value up to 50% in cold climates, whereas cellulose loses 15-20% of its R-value in similar conditions. It makes cellulose a better choice in many situations.

If you want to know more about this, refer: Fiberglass vs cellulose insulation

Which R-value is recommended for walls?

R-value requirements differ depending on your location and which part of your home needs insulation. Ceilings and attic spaces need insulation with higher R-values. For walls, the recommended R-value is between R-13 and R-23. For 2×4 walls, the R-value should be between R-13 to R-15; for 2×6 walls, the R-value should be R-19 to R-21.

Therefore you will need to use 4 to 6 inches of cellulose insulation for walls.

How can I increase the R-value in my walls?

To increase the R-value in walls or the attic, increase the amount of insulation used. Adding more insulation layers will increase the R-value of that insulation and provide better thermal resistance. It is a simple rule, double the insulation to double the R-value, and you will cut your heat loss in half.

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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