Installed cost
$900 – $2,400$900$900–$2,400$2,400
Add R-49 · 19.6 in of blown-in fiberglass · attic floor
R-value to add494949R-11 now → R-60 target
Depth needed19.6 in19.6 in19.6 inAt R-2.5 per inch
Installed per sq ft$1 – $2$0.90$0.90–$2.40$2.40
Key takeaways- Closed-cell spray foam reaches R-49 in 8.2 in, versus 19.6 in of blown-in fiberglass.
- Blown-in fiberglass is already the lowest-cost option for this job.
Installed cost estimate
- Blown-in fiberglass, 1,000 sq ft$900 – $2,400
Adding R-49: cost by material
Detailed numbers
Adding R-49 with each material| Material | R per inch | Depth needed | Installed cost |
|---|
| Fiberglass batts | 3.2 | 15.3 in | $800 – $2,600 |
|---|
| Blown-in fiberglass | 2.5 | 19.6 in | $900 – $2,400 |
|---|
| Blown-in cellulose | 3.4 | 14.4 in | $900 – $2,400 |
|---|
| Open-cell spray foam | 3.6 | 13.6 in | $1,500 – $3,500 |
|---|
| Closed-cell spray foam | 6 | 8.2 in | $3,000 – $5,000 |
|---|
Costs are per-square-foot ranges from contractor surveys and reflect a typical job depth; much deeper layers cost more.
Show the math
- Target = R-60 (DOE / ENERGY STAR attic recommendation)
- R to add = R-60 − R-11 = R-49
- Depth = R-49 ÷ R-2.5 per inch = 19.6 in
- Cost = 1,000 sq ft × $0.90–$2.40 per sq ft = $900 – $2,400