Blown-In Insulation Calculator: Bags, Depth, R-Value & Cost

● Interactive 5-Layer Attic Thermal Envelope Blueprint

Blown-In Insulation Calculator: Bags, Depth, R-Value & Cost

Click any thermal horizon on the attic blueprint below to calculate exact bags of cellulose or fiberglass, settled thickness, blower rental, and cost.

1. Attic / Wall Area Mode 1,200 sq ft

Total Area (sq ft)

2. Loose-Fill Material Type

Calibrates bag coverage chart, settling & R-value per inch.

3. Climate Zone & Target R-Value

Subtracts existing insulation R-value automatically.

4. Installation Mode & Waste 5% Buffer

0% (Exact) 5% (Standard) 15% (Dense/Slopes)

Interactive Attic Cross-Section Blueprint (Tap Any Layer)

Baffles/Vents New Blown-In Existing Joist Air Seal Deck

Include Soffit Rafter Vent Baffles (+1 per 50 sf) Include Attic Floor Top-Plate Air Sealing Include Insulated Attic Hatch / Pull-Down Dam (+$95) Vacuum / Remove Old Soiled Insulation First (+$1.35/sf)

Active Blueprint Horizon: 2. New Blown-In Loose-Fill Blanket Click below to customize this zone:

BLOWN-IN INSULATION ESTIMATE Adding R-38 (+10.3″ Settled)

Total Bags Needed

36 Bags

900 Lbs Total • 25 lb Bags

Estimated Project Cost

$1,895

Range: $1,610 – $2,235

Loose-Fill Insulation Bags (36 Bags Cellulose) $612

Blow-In Labor or Machine Rental (Pro Crew Install) $720

Attic Air Sealing & Can Light Prep (Foam & Covers) $420

Soffit Baffles, Hatch Dam & Removal (24 Baffles + Dam) $143

5. Settling Depth, Blower Rental & Ceiling Load Analyzer ✓ Free Blower Qualified

Initial vs. Settled 12.1″ → 10.3″

Drywall Load 0.75 lbs/sq ft

Blowing Time ~3.2 Hours

💡 Thermal Envelope & Blower Machine Verdict: Loading attic insulation engineering analysis…

Itemized Layer-by-Layer Blown-In Insulation Sheet

Complete bill of materials with R-value contribution, settled depth, bag count, weight, and line-item cost

5 Attic Envelope Zones Active

Blueprint Horizon	Thermal Specification	Depth / R-Value	Quantity / Bags	Total Weight / Time	Unit Rate	Est. Cost	Inspect

Compare Insulation Materials & Leading Brands Before Buying

★ Highlighted guides match your selected insulation profile

Loose-Fill Head-to-Head

Cellulose vs. Fiberglass Blown Insulation

Compare R-value per inch (R-3.7 vs R-2.7), 15% cellulose settling, air-leak resistance, fire retardancy, and bag coverage before ordering your attic material.

Compare Cellulose vs. Fiberglass →

Brand Coverage Charts

Owens Corning vs. Johns Manville Insulation

See how Owens Corning AttiCat expanding blown-in fiberglass stacks up against Johns Manville Climate Pro in bag yield, dust levels, and free blower rental minimums.

Compare Owens Corning vs. JM →

Acoustics & Fire Rating

Rockwool vs. Fiberglass Insulation

Evaluating mineral wool against standard fiberglass? Compare moisture resistance, sound deadening, thermal drift in extreme cold, and cost per square foot.

Compare Rockwool vs. Fiberglass →

Air Sealing & Rim Joists

Rockwool vs. Spray Foam

Deciding whether to air-seal your attic floor and rim joists with polyurethane spray foam or dense-pack mineral wool? Compare vapor permeability, R-value, and ROI.

Compare Rockwool vs. Spray Foam →

About This Interactive Blown-In Insulation Calculator: Key Features & Formulas

Upgrading attic insulation is one of the highest-return energy efficiency improvements for any home, slashing heating and cooling loads by 15% to 30%. However, calculating how many bags of loose-fill material to buy is tricky because cellulose, fiberglass, and mineral wool have completely different R-values per inch, bag weights, settling percentages, and coverage charts. Our interactive blown-in insulation calculator models all five layers of a high-performance attic assembly so homeowners and contractors can compute exact bag counts, initial vs. settled depth, ceiling drywall weight loads, and turnkey vs. DIY costs.

1. Net R-Value & Settled Depth Engine

Instead of guessing thickness, select your target climate zone R-value (R-30, R-38, R-49, or R-60) and subtract your existing joist insulation (R-0, R-11, R-19, or R-30). The calculator computes both initial blown thickness and final settled thickness (accounting for the 15% settling factor of cellulose).

2. Interactive 5-Layer Attic Envelope Blueprint

Click directly on any structural horizon in the SVG cross-section—Soffit Baffles & Depth Rulers, New Loose-Fill Blanket, Existing Joist Cavity, Attic Floor Air Sealing, or Scuttle Hatch Dam—to customize air sealing intensity, existing batt depth, and ventilation chutes.

3. Free Blower Machine Qualification & Load Check

Home improvement stores typically waive the $100 to $150 insulation blower rental fee when you purchase 10 to 20+ bags of cellulose or fiberglass. Our analyzer tracks whether your bag count qualifies for a free machine and verifies that total pounds per square foot stay safely below gypsum ceiling limits.

How to Use the Blown-In Insulation Calculator (Step-by-Step)

Step 1: Enter Your Attic Footprint Area Choose Direct Square Footage, Rectangle (Length × Width), or Gable + Wing Addition. Enter your attic floor dimensions to establish total square footage and perimeter soffit vent requirements.

Step 2: Choose Loose-Fill Material & Target R-Value Select Blown-In Cellulose (R-3.7 per inch), Blown-In Fiberglass (R-2.7 per inch), or Loose-Fill Mineral Wool (R-3.1 per inch), then pick your recommended target R-value from R-30 up to R-60.

Step 3: Click the Blueprint to Set Existing Insulation & Air Sealing Tap Layer 3 (Existing Joist Bay) on the blueprint to subtract existing R-11 or R-19 batts. Tap Layer 4 (Attic Floor Air Sealing) to include foam sealing around top plates, plumbing stacks, and recessed can lights before blowing new insulation.

Step 4: Compare DIY vs. Pro Cost & Print Your Shopping List Switch between Turnkey Pro Crew, Hybrid, or DIY Mode to see your exact bag count, weight in pounds, blowing time, and total cost. Click “Copy Material List” or “Print / PDF” to take your itemized sheet to the supply counter.

Blown-In Insulation Coverage Chart & Depth Rules of Thumb

To achieve the widely recommended R-49 attic standard in an uninsulated attic, blown-in cellulose requires approximately 13.3 inches of settled depth (roughly 15.6 inches initial blown depth before 15% settling), using about 40 to 44 bags per 1,000 square feet (25-lb bags). By contrast, blown-in fiberglass settles less than 2% but has a lower thermal resistance per inch, requiring roughly 18.2 inches of depth for R-49 and using approximately 28 to 32 bags per 1,000 square feet (31-lb compressed bags). If your attic already has 3.5 inches of older fiberglass or rockwool between the joists (~R-11), topping up by an additional R-38 requires roughly 10.3 inches of cellulose (30 bags per 1,000 sq ft) or 14.1 inches of fiberglass (21 bags per 1,000 sq ft).

Frequently Asked Questions (Blown-In Attic Insulation)

How many bags of blown-in insulation do I need for 1,000 sq ft? +

For a 1,000 sq ft attic, the number of bags depends on the material and desired R-value increase. To add R-30 (about 8.1 inches of cellulose or 11.1 inches of fiberglass), you need roughly 24 bags of cellulose (25-lb bags) or 17 bags of fiberglass (31-lb bags). To reach a full R-49 from an empty attic floor, expect to buy 41 to 43 bags of cellulose or 29 to 31 bags of blown-in fiberglass.

Can you blow new insulation directly over old attic insulation? +

Yes—as long as the existing fiberglass batts or loose-fill insulation are dry, free of mold, rodent contamination, or vermiculite, you can blow new cellulose or fiberglass directly over the top. Always air-seal wire holes and plumbing top plates first, install rafter vent baffles at the eaves so you do not block soffit airflow, and never place a vapor barrier between the old and new layers.

How much does blown-in insulation cost per square foot? +

Hiring a professional insulation contractor to blow attic insulation typically costs between $1.25 and $2.80 per square foot ($1,500 to $3,360 for a 1,200 sq ft attic), depending on target R-value and whether attic air sealing is included. Doing the job yourself with retail bags and a free store-loaned blower machine reduces the material cost to roughly $0.55 to $1.15 per square foot ($660 to $1,380 for 1,200 sq ft).

Will too much blown-in insulation sag or overload a 1/2-inch drywall ceiling? +

Standard 1/2-inch gypsum ceiling drywall nailed or screwed to trusses 16 or 24 inches on center is rated to support at least 2.0 to 2.2 pounds per square foot of dead load. Even a deep R-60 layer of blown-in cellulose (16.2 inches thick at 1.5 lbs/cu ft density) weighs about 2.03 lbs/sq ft, while R-60 blown-in fiberglass weighs less than 0.95 lbs/sq ft. Our calculator automatically displays your exact pounds-per-square-foot ceiling load.

Blown-In Insulation Calculator: Bags, Depth, R-Value & Cost