How Much Insulation for a 1,000 Sq Ft Attic?
Quick Answer
For a 1,000 sq ft attic targeting R-38, you need about 32 rolls of R-38 fiberglass batts or 30 to 40 bags of blown-in cellulose. Cold climates targeting R-49 need about 40 rolls.
- R-38 fiberglass batts: ~32 rolls
- R-49 fiberglass batts: ~40 rolls (cold climates)
- Blown-in cellulose (R-38): 30–40 bags
- Add 10% for irregular joist spacing and obstacles
Formula
Divide attic square footage by the coverage per roll from the packaging. For 16-inch OC joists, each R-38 roll covers about 32 sq ft.
Step-by-Step Calculation
- 1
Attic area
1,000 sq ft
- 2
R-38 batts (32 sq ft per roll)
1,000 ÷ 32 = 31.25 → 32 rolls
- 3
Blown-in cellulose
1,000 × 0.03–0.04 bags/sq ft = 30–40 bags
- 4
Add 10% waste
32 × 1.10 = 35 rolls
Insulation for 1,000 Sq Ft Attic by Type
| Insulation Type | R-Value | Depth | Quantity | Material Cost* |
|---|---|---|---|---|
| Fiberglass Batts | R-30 | ~10" | 27 rolls | $400–$650 |
| Fiberglass Batts | R-38 | ~12" | 32 rolls | $500–$800 |
| Fiberglass Batts | R-49 | ~16" | 40 rolls | $635–$1,000 |
| Blown-In Cellulose | R-38 | ~10.5" | 34 bags | $335–$535 |
| Blown-In Fiberglass | R-38 | ~14" | 37 bags | $435–$665 |
*Materials only. Professional installation adds $0.50–$1.50 per sq ft.
Frequently Asked Questions
What R-value do I need for a 1,000 sq ft attic?
Most climates target R-38 (about 12 inches of batts). Cold northern zones aim for R-49 to R-60, while mild southern zones may only require R-30. Check your local energy code for the exact target.
Batts or blown-in for a 1,000 sq ft attic?
Blown-in is faster and fills gaps and odd spaces well, making it popular for attic floors. Batts suit open, evenly spaced joists and DIY work. Both reach the same R-value when installed to the right depth.
How much does it cost to insulate a 1,000 sq ft attic?
Materials run about $400–$1,000 by type and R-value. Professional installation adds $500–$1,500, for a typical total of $900–$2,500 for a 1,000 sq ft attic.