Blown-In Fiberglass Insulation
Blown-in fiberglass insulation consists of loose glass fibers that are pneumatically installed using a blowing machine. This method is particularly effective for attic floors where it can be blown over existing insulation to increase the total R-value, and for dense-packing existing wall cavities through small access holes. The loose-fill format conforms to irregular spaces, around wiring and plumbing, and fills gaps that batt insulation often misses. The R-value per inch is lower than batts due to the lower density of the installed product, but the superior coverage typically results in better real-world thermal performance. Professional installation is recommended to achieve proper density and uniform coverage.
Blown-In Fiberglass Specifications
Best Applications for Blown-In Fiberglass
Blown-In Fiberglass is recommended for the following building components. Each application link shows the specific R-value requirements by climate zone and how Blown-In Fiberglass compares against other insulation options for that component.
Thickness Required by Climate Zone
The table below shows the thickness of Blown-In Fiberglass needed to achieve the DOE recommended R-value for each building component in every climate zone. Cells showing "N/R" indicate that insulation is not required for that component in that zone. Use this table to quickly determine how much Blown-In Fiberglass you need for your specific zone and application.
| Zone | Attic | Wall Cavity | Wall Cont. | Floor | Basement | Crawlspace | Cathedral | Garage |
|---|---|---|---|---|---|---|---|---|
| Zone 1 | 12" | 5.2" | N/R | 5.2" | N/R | N/R | 8.8" | 7.6" |
| Zone 2 | 15.2" | 5.2" | N/R | 5.2" | N/R | N/R | 8.8" | 7.6" |
| Zone 3 | 15.2" | 5.2" | N/R | 7.6" | 2" | 2" | 12" | 7.6" |
| Zone 4 | 19.6" | 5.2" | 2" | 10" | 4" | 4" | 15.2" | 12" |
| Zone 5 | 19.6" | 5.2" | 2" | 10" | 4" | 4" | 15.2" | 12" |
| Zone 6 | 24" | 5.2" | 4" | 10" | 6" | 4" | 19.6" | 15.2" |
| Zone 7 | 24" | 5.2" | 4" | 10" | 6" | 4" | 19.6" | 15.2" |
| Zone 8 | 24" | 5.2" | 6" | 10" | 7.6" | 4" | 19.6" | 15.2" |
Cost Estimates by Climate Zone (per 1,000 sq ft)
Material cost estimates for Blown-In Fiberglass at the DOE recommended R-value for each climate zone and component. These are material costs only and do not include labor. Professional installation typically adds 50-100% to the material cost shown below.
| Zone | Attic | Wall Cavity | Wall Cont. | Floor | Basement |
|---|---|---|---|---|---|
| Zone 1 | $2,400 | $1,040 | N/R | $1,040 | N/R |
| Zone 2 | $3,040 | $1,040 | N/R | $1,040 | N/R |
| Zone 3 | $3,040 | $1,040 | N/R | $1,520 | $400 |
| Zone 4 | $3,920 | $1,040 | $400 | $2,000 | $800 |
| Zone 5 | $3,920 | $1,040 | $400 | $2,000 | $800 |
| Zone 6 | $4,800 | $1,040 | $800 | $2,000 | $1,200 |
| Zone 7 | $4,800 | $1,040 | $800 | $2,000 | $1,200 |
| Zone 8 | $4,800 | $1,040 | $1,200 | $2,000 | $1,520 |
Advantages and Limitations
Every insulation type has trade-offs that affect its suitability for different applications. Understanding these trade-offs helps you select the right insulation for your specific project requirements, budget, and installation constraints.
Advantages of Blown-In Fiberglass
- Low material cost makes it budget-friendly for large areas
- Non-combustible — no thermal barrier required in most applications
- Well-suited for: Attic, Wall Cavity
Limitations of Blown-In Fiberglass
- Low R-value per inch requires greater thickness
- Requires professional installation — not suitable for DIY
- Poor moisture resistance — not suitable for wet or below-grade locations
Compare Other Insulation Types
Browse specifications and cost analysis for other insulation materials to find the best option for your project.