“How much R-value does blown-in insulation have per inch?”
With blown-in insulation (also referred to as loose-fill insulation), the R-value per inch is the key data point. Blown-in insulation can have R-values from R-1 per inch and up to R-3.4 per inch (loose-fill cellulose). We are going to list all blown-in insulation R-values per inch (check the chart below).
Namely, we use blowing machines to add loose-fill insulation. To adequately plan the overall R-value, we need to know what is the R insulation value per inch for these blown-in insulation materials.
Example: In California, you need R-49 to R-60 attic insulation (you can check the recommended attic R-values chart here). How thick should you blow the loose-fill insulation? The prerequisite for calculating this accurately is by knowing what is the R-value per inch of your insulation material.
Not all blown-in insulation materials have the same R-value. This loose-fill insulation is made out of small particles of cellulose, rock or mineral wool, fiberglass, perlite, vermiculite, and even wood chips.
Each type of blown-in insulation has its own insulation R-values per inch, with blown-in cellulose having the highest R-3.4 per inch insulation capacity.
Here is the chart that lists all major blown-in insulation R-values per inch, per 2-inches, per 4-inches, and per 8-inches (with commentary):
Blown-In Insulation R-Value Chart (Per 1, 2, 4, 8 Inches Thickness)
| Blown-In Insulation Material: | R-Value Per Inch: | 2 Inch R-Value: | 4 Inch R-Value: | 8 Inch R-Value: |
| Blown-In Cellulose | R-3.4 Per Inch | R-6.8 | R-13.6 | R-27.2 |
| Blown-In Wool | R-3.1 Per Inch | R-6.2 | R-12.4 | R-24.8 |
| Blown-In Fibergrass | R-3.1 Per Inch | R-6.2 | R-12.4 | R-24.8 |
| Blown-In Perlite | R-2.7 Per Inch | R-5.4 | R-10.8 | R-21.6 |
| Blown-In Vermiculite | R-2.25 Per Inch | R-4.5 | R-9 | R-18 |
| Blown-In Wood (Wood Chips) | R-1 Per Inch | R-2 | R-4 | R-8 |
As you can see, the blown-in insulation materials are listed from the highest R-value (cellulose) to the lowest R-value (wood chips). The best per-inch loose-fill insulation material is cellulose, followed closely by mineral wool and fiberglass:
- Blown-in cellulose has an R-3.4 per inch insulation value. If you blow an 8-inch layer, you are adding R-27.2 of insulation.
- Blown-in mineral wool has an R-3.1 per inch insulation value. If you blow an 8-inch layer, you are adding R-24.8 of insulation.
- Blown-in fiberglass has an R-3.1 per inch insulation value. If you blow an 8-inch layer, you are adding R-24.8 of insulation.
- Blown-in perlite has an R-2.7 per inch insulation value. If you blow an 8-inch layer, you are adding R-21.6 of insulation.
- Blown-in vermiculite has an R-2.25 per inch insulation value. If you blow an 8-inch layer, you are adding R-18 of insulation.
- Blown-in wood chips have an R-1 per inch insulation value. If you blow an 8-inch layer, you are adding R-8 of insulation.
This explains why we use loose-fill cellulose, mineral wool, and fiberglass for heavy insulation rooms (like the attic). In most cases, you will see blown-in cellulose use over mineral wool because it is cheaper (usually made from recycled newsprints).
Loose-fill perlite and vermiculite were used in the past; you will almost never see them in new constructions. The same goes for wood chips. The listed R-values per inch here can help you calculate the R-value of existing buildings.
Hopefully, this chart illustrates well the R-values of blown-in insulation materials and will help you adequately calculate what thickness of blown-in insulation you need. If you have any questions or suggestions, you can freely use the comment section below.