Blow In Insulation Calculator
Free calculator to estimate blown-in insulation needs. Calculate bags, depth, and cost for cellulose or fiberglass insulation based on your area and target R-value.
Quick Reference (per 1,000 sq ft at R-38)
Cellulose: ~37 bags, 10.3" depth, $700-$900 DIY | Fiberglass: ~55 bags, 15.2" depth, $550-$750 DIY
📐 Project Details
Eco-friendly, made from recycled paper • R-3.7/inch
R-values are cumulative. Enter 0 if starting fresh.
📊 Estimate
Bags Needed
47
25 lb bags of Cellulose
📋 Project Details
💰 Estimated Cost
💡 Tip: Home Depot & Lowe's offer free 24-hour machine rental with purchase of 10+ bags.
📊 Cellulose vs Fiberglass Comparison
| Feature | Cellulose | Fiberglass |
|---|---|---|
| R-Value per Inch | R-3.7 ✓ | R-2.5 |
| Cost (DIY per sq ft) | $0.60-$1.20 | $0.40-$1.00 ✓ |
| Eco-Friendly | 85% recycled ✓ | 20-30% recycled |
| Fire Resistance | Treated (Class 1) | Naturally non-flammable ✓ |
| Moisture Resistance | Can absorb moisture | Moisture resistant ✓ |
| Air Sealing | Excellent ✓ | Good |
| Settling Over Time | May settle 15-20% | Minimal settling ✓ |
* Both materials are effective insulators. Cellulose is better for air sealing and eco-friendliness; fiberglass is better for humid climates and longevity.
🏠 What is Blow-In Insulation?
Blow-in insulation (also called loose-fill insulation) is a type of thermal insulation that's installed using a blowing machine. Small particles of cellulose, fiberglass, or mineral wool are blown into attics, walls, and other spaces to create an effective thermal barrier.
Why Choose Blown-In Insulation?
Better coverage: Blown insulation fills gaps, cracks, and irregular spaces that batt insulation can't reach. Easy installation: DIY-friendly with free machine rental at most home improvement stores. Cost-effective: Lower material cost per R-value compared to spray foam. Flexible: Can be added over existing insulation to boost R-value.
DIY vs Professional Installation
DIY installation can save 40-50% on costs. Most homeowners can insulate an attic in 4-8 hours with a helper. Home Depot and Lowe's offer free 24-hour machine rental with purchase of 10+ bags. Professional installation is recommended for wall cavities, hard-to-reach areas, or if you prefer guaranteed results with warranty coverage.
📐 Quick Depth Guide
R-30 → 8" cellulose / 12" fiberglass
R-38 → 10" cellulose / 15" fiberglass
R-49 → 13" cellulose / 20" fiberglass
R-60 → 16" cellulose / 24" fiberglass
💰 Save on Energy Bills
Proper attic insulation can reduce heating/cooling costs by 15-25% annually.
Average savings: $200-$600/year depending on climate and home size.
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Frequently Asked Questions
To calculate blown insulation needs: 1) Measure the area in square feet (length × width), 2) Determine your target R-value based on climate zone and location (attic, wall, floor), 3) Divide target R-value by the material's R-value per inch to get required depth, 4) Calculate cubic feet needed (area × depth ÷ 12), then divide by coverage per bag. Our calculator automates this process for you.
For 1,000 sq ft at R-38 (common attic target): Cellulose requires about 37-40 bags (25 lb bags), while fiberglass needs approximately 55-60 bags. At R-30, you'll need roughly 30-33 bags of cellulose or 45-50 bags of fiberglass. The exact number depends on your target R-value and whether you have existing insulation.
To achieve R-30: Cellulose blown insulation requires approximately 8-8.5 inches of depth (R-3.7 per inch). Fiberglass loose-fill needs about 11-12 inches (R-2.5 per inch). High-density fiberglass requires roughly 10-11 inches (R-2.8 per inch). Always verify with manufacturer specifications as R-values can vary slightly by brand.
For a 2,000 sq ft attic at R-49: Cellulose requires about 75-80 bags (25 lb), costing $1,200-$1,800 DIY or $2,800-$3,600 professionally installed. Fiberglass needs 100-110 bags, costing $1,000-$1,600 DIY or $2,200-$3,000 installed. Wall insulation adds additional cost depending on wall cavity access.
Both have advantages: Cellulose offers higher R-value per inch (3.7 vs 2.5), better air sealing, and is eco-friendly (recycled paper). It's ideal for attics and retrofit projects. Fiberglass is moisture-resistant, non-flammable, doesn't settle as much, and works better in humid climates. Fiberglass costs less upfront but requires more depth for the same R-value.
Yes, blown insulation can be added over existing insulation if it's dry and in good condition. R-values are cumulative—if you have R-19 and add R-30, you'll achieve approximately R-49. Before adding, check for moisture damage, pest infestation, or compressed/damaged insulation. Remove any vapor barriers from the new layer to prevent moisture trapping.
🏠 Disclaimer: This calculator provides estimates for planning purposes only. Actual material needs may vary based on installation technique, settling, and specific product specifications. Always check manufacturer coverage charts and local building codes before purchasing materials.