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.
Pro Tips
- At 1,000 sq ft, this is a quick blown-in cellulose job — two people with a blower machine can finish in 3–4 hours including setup and cleanup. Buy 30–40 bags to hit R-38 and use the free blower from the retailer.
- Before blowing insulation, walk the attic and create a map of obstacles: HVAC ductwork, electrical junction boxes, recessed light housings, and plumbing vents. Mark each one with a flag so they are visible during the blow — burying a junction box creates a fire hazard and a code violation.
- Install foam baffles at every rafter bay along the eaves (typically 30–40 baffles for 1,000 sq ft). These cost $1–$2 each ($30–$80 total) and prevent blown insulation from blocking soffit ventilation — blocked soffits cause ice dams and attic moisture problems.
- If your attic has existing batts with gaps and compressions, blow cellulose right over them. The loose-fill cellulose fills all the gaps the batts missed, significantly improving the overall insulation performance without removing the old material.
Key Cost Factors
- Blown cellulose for 1,000 sq ft at R-38: 30–40 bags at $11–$15 each = $330–$600. Baffles: $30–$80. Total DIY: $360–$680. This is one of the most cost-effective home improvements available — expect $150–$300/year in energy savings, meaning payback in 1.5–4 years.
- Professional insulation for 1,000 sq ft runs $1,500–$3,000 installed. The DIY savings of $1,100–$2,400 are substantial relative to the 3–4 hours of work required. This is one of the easiest and highest-ROI DIY projects for any homeowner with attic access.
Common Mistakes to Avoid
- Wrong R-value for the climate. A 1,000 sq ft attic needs R-38 to R-60 by zone; under-insulating wastes energy long-term.
- Blocking soffit vents. Insulation packed into the eaves stops airflow and causes moisture and ice dams; use baffles.
- Skipping air sealing. Seal penetrations and top plates before insulating so air does not bypass the added R-value.
- Compressing the material. Crushed batts or under-depth loose-fill deliver less than their rated R-value.
Related Project Considerations
- Choose blown-in or batts. Blown-in fills irregular framing well and is quick even over 1,000 sq ft; batts suit open, evenly spaced joists.
- Protect recessed lights. Keep insulation clear of non-IC-rated fixtures or upgrade them to avoid a fire hazard.
- Seal and insulate the hatch. Weatherstrip the access and add a rigid insulated cover to stop a common heat leak.
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 fiberglass batts or 10 inches of blown cellulose). Cold northern zones (6–7) 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 — meeting code is usually the minimum for resale value, and exceeding it by one tier often pays back in 5–7 years through lower energy bills.
Batts or blown-in for a 1,000 sq ft attic?
Blown-in cellulose or fiberglass is faster to install and fills gaps, odd joist spacing, and areas around wiring and plumbing much more thoroughly than batts. Batts suit open, evenly spaced joists in new construction where you can lay them flat without compressing them against obstacles. Both reach the same R-value when installed to the correct depth — the key is avoiding gaps, compression, and voids regardless of type.
How much does it cost to insulate a 1,000 sq ft attic?
Materials run about $400–$1,000 depending on insulation type and target R-value. Professional installation adds $500–$1,500, for a typical total of $900–$2,500 for a 1,000 sq ft attic. The DOE estimates that proper attic insulation saves 10–50% on heating and cooling costs, so payback periods of 2–5 years are common — making it one of the best energy-efficiency investments for any home.