Attic Insulation Calculator
Calculate attic insulation calculator bags depth r-38 r-49. Precise material estimations for building contractors and DIY home builders across USA/UK/Canada.
Calculate Attic Insulation Calculator
Enter project dimensions below to compute required material quantities.
Calculation Results
Calculated using verified construction formula: Cellulose Bags = Math.ceil( (Attic Length * Attic Width / 1000) * (Target R-Value / 30) * 32 )
Quick Summary
The Attic Insulation Calculator computes blown-in loose-fill cellulose 30lb bags, required settled depth in inches (R-38, R-49, R-60), blowing machine rental days, total attic floor weight load, and material costs.
- Attic R-Value Depth Scoping: Measures settled insulation depth for R-38 (12 in depth), R-49 (16 in depth), and R-60 (20 in depth).
- Blown-In Bag Scoping: Calculates 30lb loose-fill cellulose bags (approx 32 bags per 1,000 sq ft for R-30).
- Free Blowing Machine Rental: Itemizes blowing machine rental terms (home centers offer free 24-hour machine rental with 20+ bag purchase).
How to Use the Attic Insulation Calculator
- Enter Attic Length in feet.
- Enter Attic Width in feet.
- Select Target Attic R-Value (R-38 standard 12-inch depth).
- Select Insulation Material (Blown-In Loose-Fill Cellulose standard).
- Click Calculate to view 30lb cellulose bags, settled depth, blowing machine rental days, weight load, and cost.
Attic Insulation Calculator Formula & Method
This tool utilizes verified construction geometric formulas to compute material requirements:
Bags (30lb) = Math.ceil( (Attic Sq Ft / 1000) * (Target R / 30) * 32 )
Settled Depth = Target R / 3.2 R-per-inch
Where:
- Loose-Fill Cellulose: Borate-treated recycled paper insulation blown through a hose onto attic floors.
- Settled Depth: Final thickness of blown insulation after natural settling over 6 months.
- R-38 Standard: Recommended US Department of Energy attic insulation benchmark for Climate Zones 2 through 4.
Worked Example
Example: 40ft * 30ft Attic Floor (1,200 sq ft) Blown to R-38 (12-Inch Depth)
- Attic Floor Area: 40 ft * 30 ft = 1,200 sq ft
- Required R-38 Depth: 12.0 inches settled depth
- Blown Cellulose Bags Needed: (1,200 / 1000) * (38 / 30) * 32 = 49 Bags (30 lb)
Applying the formula yields:
Total 30lb Cellulose Bags: 49 Bags
Settled Insulation Depth: 12.0 Inches (R-38)
Blowing Machine Rental: FREE (with 20+ bags)
Estimated Material Cost: 1,200 * .25 = ,500.00
What This Calculator Includes vs. Does Not Include
What This Calculator Includes
- Attic Blown-In Insulation Engineering: Measures 30lb cellulose bags, settled depth in inches, blowing machine rental terms, attic floor weight loads, and material costs.
- IECC Climate Zone R-Value Benchmarks: Provides depth calculations for R-38, R-49, and R-60.
What This Calculator Does Not Include
- Radiant Barrier Foil Sheathing Installation: Aluminum radiant barrier foil.
Tips & Best Practices
- Install Attic Cardboard Rulers on Trusses: Staple cardboard attic height rulers onto roof trusses every 10 feet before blowing insulation so you can easily verify 12 to 16 inches of depth.
- Wear an N95 Dust Mask and Goggles: Blowing loose-fill insulation generates heavy paper dust in confined attic spaces; wear a protective N95 mask and sealed safety goggles.
Common Mistakes to Avoid
- Covering Recessed Can Lights Without IC Ratings: Blowing insulation over non-IC rated recessed ceiling light fixtures creates a fire hazard; build a 3-inch clearance drywall box over non-IC lights.
Frequently Asked Questions (FAQ)
How many bags of blown-in insulation for a 1,200 sq ft attic?
A 1,200 sq ft attic requires 49 30lb bags of blown-in cellulose insulation for R-38 (12-inch depth).
How thick is R-38 blown-in cellulose insulation?
R-38 blown-in cellulose is 12 inches thick (settled depth).
How thick is R-49 blown-in cellulose insulation?
R-49 blown-in cellulose is 15.5 to 16 inches thick (settled depth).
Is the insulation blowing machine rental free?
Yes. Home Improvement stores (Home Depot / Lowe's) provide a free 24-hour insulation blower rental when purchasing 20 or more bags.
How long does it take to blow an attic with insulation?
Blowing a 1,200 sq ft attic (49 bags) takes two people approximately 2 to 3 hours.
Can I blow new cellulose over old fiberglass insulation?
Yes. Blowing new cellulose insulation over existing fiberglass fills air gaps and significantly increases overall attic R-value.
How heavy is 50 bags of cellulose insulation on an attic ceiling?
50 30lb bags weigh 1,500 lbs total (approx 1.25 lbs per sq ft on 1,200 sq ft ceiling drywall).
What is the difference between blown cellulose and blown fiberglass?
Cellulose is denser (R-3.7/in) and blocks air draft currents better; fiberglass is lighter (R-3.1/in) and non-combustible.
Is this attic insulation calculator free to use?
Yes, TibCal's Attic Insulation Calculator is 100% free.