Guides / Insulation · Updated
How many bags of GreenFiber cellulose do you need?
GreenFiber SANCTUARY blown cellulose, 25 lb bags, loose-fill attic chart. From GreenFiber's attic card (Rev K, May 2026).
Short answer
Find your R-value below, then divide your attic's square feet by the square feet per bag and round up.
| R-value | Blow to (in) | Settles to (in) | Sq ft per bag (max) | Bags per 1,000 sq ft |
|---|---|---|---|---|
| R13 | 3.9 | 3.6 | 65.8 | 16 |
| R19 | 5.7 | 5.3 | 44.2 | 23 |
| R22 | 6.6 | 6.1 | 38 | 27 |
| R30 | 8.9 | 8.3 | 25.9 | 39 |
| R38 | 11.2 | 10.4 | 19 | 53 |
| R44 | 12.9 | 12 | 15.7 | 64 |
| R49 | 14.3 | 13.3 | 14.1 | 71 |
| R60 | 17.3 | 16.1 | 11.6 | 87 |
Cellulose settles. GreenFiber's chart is based on settled thickness, so blow it to the deeper number; it sinks to the settled depth over time and that's when it reaches the R-value. Count bags, not inches: the chart's bags per 1,000 sq ft is what sets the R-value.
Bags for common attic sizes
| Attic floor | R30 | R38 | R49 | R60 |
|---|---|---|---|---|
| 600 sq ft | 24 | 32 | 43 | 52 |
| 800 sq ft | 31 | 43 | 57 | 69 |
| 1,000 sq ft | 39 | 53 | 71 | 87 |
| 1,200 sq ft | 47 | 64 | 86 | 104 |
| 1,500 sq ft | 58 | 79 | 107 | 130 |
| 2,000 sq ft | 78 | 106 | 142 | 173 |
Rounded up. Add a bag or two for the hatch, corners and mistakes.
Which R-value
ENERGY STAR recommends R30 in climate zone 1, R49 in zones 2 and 3, and R60 in zones 4 to 8. If there's already insulation up there, you add less: the attic insulation calculator finds your zone by ZIP, takes off what you have, and counts the bags.
Source: GreenFiber SANCTUARY attic coverage card. Compare brands in theattic insulation calculator.