Blown-In Insulation Calculator

Estimate bag counts, understand blower rental terms from Home Depot and Lowe's, choose between dense-pack and loose-fill, and follow the pre-blow air-sealing checklist that determines how well your finished R-value holds up — with sourced figures from DOE and IRC.

How Does Blower Rental Work at Home Depot and Lowe's?

Both major home-improvement retailers loan an insulation blower machine free when you purchase a qualifying minimum number of bags. The details differ by store:

• Home Depot: the first day's rental (24 hours) is free with purchase of 10 or more bags of their cellulose loose-fill product. A refundable deposit of approximately $250 is held until the machine is returned.
• Lowe's: a free 24-hour machine rental is offered with purchase of 20 or more bags of qualifying loose-fill products (terms vary by location).

Call your local store before you buy to confirm machine availability — blowers can be reserved and stock is limited. Return the machine the same day; most stores do not offer multi-day free-rental extensions.

The rental blower connects to a standard household electrical outlet (120 V / 15 A). A 50-foot fill hose is typically included. If your attic access point is farther from the machine than 50 feet, plan to run extension hoses or reposition the machine — do not loop or kink the hose, which reduces material flow. A two-person crew is strongly encouraged: one person feeds bags into the hopper, the other directs the hose inside the attic.

Blower Rental + Bag Pairing — What's Available Where

The blower machine and the bag product are a matched system: the rental blower's hopper opening, shredder speed, and output pressure are calibrated to the manufacturer's bag product. Owens Corning AttiCat uses a dedicated AttiCat Expanding System blower (model L77) available at Home Depot locations that stock AttiCat bags. GreenFiber Cocoon bags pair with the standard loose-fill cellulose blower stocked at Lowe's and many independent insulation suppliers. A two-person crew with a standard rental blower can move approximately 30–50 bags per hour under typical attic conditions with a 50-ft hose.

Note: Deposit amounts and minimum bag counts are approximate and store-specific — call your local Home Depot or Lowe's to confirm before planning your install.

Both Home Depot and Lowe's offer the rental term as one 24-hour period — not a calendar day. If you pick up the machine at 2 pm, it is due back by 2 pm the following day. Plan your project around this window. For a 1,500 sq ft attic at R-38 (~87 bags of cellulose), a two-person crew at 30–40 bags/hr can complete the blow-in in 2–3 hours, leaving time for setup, air-sealing, and post-install inspection within the 24-hour window.

Equipment Time Estimates for DIY Blow-In

For a typical unconditioned attic floor with bare joists and no major obstructions, a two-person team using a rented blower can expect:

These figures assume no existing insulation and a first-time DIY crew. Experienced crews are faster. Tightly framed attics with many obstructions (HVAC ducts, multiple hatch locations, low headroom) add 30–60 minutes per 500 sq ft. Plan the air-sealing step (below) before starting the blow-in — add 2–4 hours for a thorough air-seal.

Blown Cellulose Bag Count Reference — per 1,000 sq ft

The table below shows approximate bag counts for blown cellulose at common R-value targets for a 1,000 sq ft attic floor with bare joists. Bag size assumed: 30 lb bags at 3.7 R/inch settled performance. Actual coverage varies by brand — always cross-check the coverage chart on your specific bag label.

For a brand-by-brand bag-count comparison (GreenFiber Cocoon vs Applegate vs Owens Corning AttiCat), see our attic insulation guide brand comparison table.

What Is the Difference Between Dense-Pack and Loose-Fill Blown-In Insulation?

Blown cellulose is installed at two fundamentally different densities depending on the application. The density determines settling behavior, air resistance, and the equipment settings needed.

Loose-Fill (Attic Floors)

Loose-fill cellulose for attic floors is blown to a settled density of approximately 1.5 lb per cubic foot. At this density the material conforms around joists, wiring, and ducts without requiring high blower pressure. After installation, loose-fill cellulose settles an additional 15–20% over the first few years; bag-coverage charts from manufacturers already account for this settling factor. Blown fiberglass is lighter still — typically 0.5–0.6 lb per cubic foot — which is why it requires a greater depth to reach the same R-value as cellulose.

The formula for depth at a given R-value target is: depth (inches) = target R ÷ R-per-inch. For cellulose at 3.7 R/inch, R-49 requires 49 ÷ 3.7 = 13.2 inches of settled depth. For blown fiberglass at 2.5 R/inch, R-49 requires 49 ÷ 2.5 = 19.6 inches — roughly 50% more depth for the same R-value.

Dense-Pack (Wall Cavities)

Dense-pack cellulose for enclosed wall cavities is blown to 3.5 lb per cubic foot or higher. At this density the material resists settling and creates a semi-rigid plug that reduces convective air loops within the cavity. Dense-pack requires a fill tube inserted to the bottom of the cavity and slowly withdrawn as material fills the space — a technique different from attic blowing. Achieving consistent 3.5 lb/cu ft density requires a calibrated blower, a flow meter, and experience reading back-pressure on the hose. Under-packed cavities (below 3.0 lb/cu ft) settle and create voids; hiring a weatherization contractor for wall work often makes sense for this reason.

When Should I Use Wet-Spray vs Dry-Blown Cellulose?

Cellulose insulation is available in two distinct application modes. Using the wrong mode for the wrong surface increases cost and reduces performance.

Dry-blown cellulose is the method used in the vast majority of attic retrofits. Wet-spray cellulose is a new-construction technique applied to open stud cavities by specialty contractors before the drywall is hung. The two methods are not interchangeable. The DOE EnergySaver insulation guide covers application types and R-value targets by climate zone. For a deep-dive on cellulose chemistry — borate vs ammonium-sulfate fire retardants and 18-20% settling behavior — see our cellulose insulation calculator guide (R-49 → ~50-67 bags/1,000 sq ft depending on brand).

Wall-Cavity Blown-In: The Drill-and-Fill Retrofit

Adding blown-in insulation to existing enclosed wall cavities — a common retrofit in homes built before 1980 — follows a different process than attic work. The wall cavities are accessed by drilling 2.5–3 inch holes, typically through the exterior siding or interior drywall, at the top of each stud bay. A fill tube is inserted and dense-pack cellulose is blown in. The holes are then patched and painted.

Key considerations for drill-and-fill:

• Fire blocks and blocking: older homes often have horizontal fire-blocking boards mid-wall. Each blocked cavity requires a second drill hole below the block. Locate fire blocks by drilling a pilot hole and probing before committing to the full hole pattern.
• Wiring runs: confirm wiring location before drilling. Knob-and-tube wiring in pre-1950 homes may be present inside wall cavities; consult an electrician before adding insulation, as covering K&T wiring with insulation creates a heat-buildup hazard.
• IRC reference: IRC N1102.1 ↗ sets minimum wall-assembly R-values by climate zone; confirm the target R-value before specifying density.
• Cost vs spray foam: drill-and-fill cellulose typically costs $1.50–$2.50 per square foot of wall area installed by a contractor, compared to $3–$5 per square foot for two-component spray foam in closed wall cavities. Spray foam achieves a slightly higher R-per-inch but requires a licensed applicator in most jurisdictions.

What Are Common Blown-In Installation Mistakes?

Four mistakes account for the majority of DIY blown-in insulation performance shortfalls. Each is avoidable with the right pre-work.

• Compressing cellulose during install. Running the blower hose too close to the surface as material accumulates compresses loose-fill cellulose and reduces its R-value by 10–15% at densities above 2.0 lb/cu ft. Keep the hose outlet at least 18 inches above the settled surface and work in sweeping passes.
• Blocking soffit vents with insulation. IRC §R806.3 ↗ requires a 1:150 ventilation ratio (or 1:300 with balanced ridge and soffit venting) for vented attic assemblies. Without rafter baffles, blown material can completely cover soffit vent openings within a few hours of install, causing moisture buildup and accelerated roof sheathing decay. Install rigid rafter baffles at every rafter bay before blowing.
• Insufficient depth at the perimeter. The attic perimeter near the eaves has the shallowest joist bay and is the area most prone to underinsulation. As material settles 15–20%, shallow perimeter depths that appeared adequate at install time end up below the R-value target. Use depth ruler sticks (included with most rentals) and measure at the eaves specifically.
• Skipping air-sealing before blowing. The DOE estimates that air-sealing before insulating saves 15–30% on heating and cooling costs beyond what insulation alone achieves. Blown cellulose does not seal air gaps — it fills space. Seal all top-plate gaps, recessed-light rough-ins, and pipe penetrations first.

Blown-In vs Closed-Cell Spray Foam: When to Choose Each

Blown-in insulation and closed-cell spray foam serve different structural and performance roles. The decision hinges on application context, budget, and whether a built-in vapor retarder is required.

Choose blown-in when: the project is an open attic floor with standard joist bays; you have access to the $0 blower rental at Home Depot (≥10 bags) or Lowe's (≥20 bags); the wall cavity is accessible for drill-and-fill dense-pack; or your climate zone does not require a Class II vapor retarder (Zones 1–3 per IRC N1102.4 ↗). DIY material cost runs $0.40–$0.80 per sq ft at R-49 depending on product.

Choose closed-cell spray foam when: the assembly requires a built-in Class II or Class I vapor retarder (Zones 5–8 cathedral ceilings, unvented roof assemblies); wall cavities need structural shear contribution from the foam layer; or the application surface is irregular and cannot be reached with a blow-in hose. Closed-cell spray foam runs $3–$5 per sq ft contractor-installed — three to six times the cost of blown-in cellulose — and requires a licensed applicator. It is not a DIY product.

For most retrofit attic projects in Climate Zones 1–5, blown cellulose at $0.50–$0.80 per sq ft provides comparable R-value performance at a fraction of spray foam's cost. The 30% Energy Star 25C tax credit (up to $1,200/year, through 2032 per energystar.gov) applies to qualifying insulation materials and installation labor, further improving the cost-effectiveness of the blown-in approach.

What Does Blown-In Insulation Cost?

Blown-in insulation cost varies by material type (cellulose vs fiberglass), whether the project is DIY or contractor-installed, and the R-value target required by your climate zone. The figures below reflect 2024–2026 retail pricing at major home improvement retailers and published contractor-installed ranges.

DIY Material Cost

At R-49, a 1,000 sq ft attic requires approximately 55 bags of cellulose or 38 bags of blown fiberglass. At retail pricing of $9–$14 per bag, the material cost runs $500–$800 per 1,000 sq ft for cellulose at R-49. Blown fiberglass (Owens Corning AttiCat) costs approximately $400–$650 per 1,000 sq ft at R-49 — slightly lower in material outlay, but requiring 20 inches of depth versus 13 inches for cellulose at the same R-value.

Blower rental cost: $0 with qualifying bag purchase (Home Depot ≥10 bags, Lowe's ≥20 bags; refundable $150–$250 deposit required). For a 1,000 sq ft attic at R-49, you will clear the 10-bag threshold at Home Depot without buying a single extra bag, making the effective blower cost $0. Blower-only rental without qualifying bag purchase runs approximately $70–$100 per day.

Contractor-Installed Cost

Contractor-installed blown cellulose typically runs $1.20–$2.00 per sq ft for open attic floor applications, including materials, labor, and equipment. For a 1,500 sq ft attic at R-49, that is roughly $1,800–$3,000 fully installed. Wall-cavity drill-and-fill cellulose runs $1.50–$2.50 per sq ft of wall area — compared to $3–$5 per sq ft for closed-cell spray foam in equivalent wall cavities.

Energy Savings and Tax Credits

DOE EnergySaver research shows adding attic insulation to meet or exceed DOE recommendations reduces heating and cooling costs by 15–30% annually. For a home spending $2,400/year on HVAC, that is a potential saving of $360–$720 per year — a payback period of roughly 2–5 years on a DIY cellulose install.

The IRS Energy Efficient Home Improvement Credit (Section 25C, extended through 2032) covers 30% of the cost of insulation materials and labor, up to $1,200 per year. Blown cellulose and blown fiberglass both meet the Energy Star qualifying requirements for 25C. See energystar.gov/about/federal_tax_credits for qualification details. Consult a tax professional for your specific situation.

Cellulose and fiberglass blown-in insulation may qualify for the federal Energy Star 25C tax credit (30% of materials + labor up to $1,200/year, expired Dec 31 2025 — see our attic insulation guide for current status).

Air-Sealing Before You Blow: The Critical First Step

The U.S. Department of Energy estimates air-sealing before insulating saves 15–30% on heating and cooling costs beyond what insulation alone achieves. Blown-in insulation does not seal air gaps — it fills space. Skipping air-sealing is the most common DIY mistake in attic insulation projects.

Seal these locations before blowing:

1. Top-plate gaps: the gap where interior partition walls meet the attic floor is often unsealed in older construction. Use low-expansion spray foam (12 oz cans) for gaps up to 1 inch; use rigid foam board plus canned foam for larger openings.
2. Recessed (can) lights: standard IC-rated recessed lights have significant air leakage. An airtight cover box (rigid foam or metal) placed over each fixture from the attic side blocks this path. Confirm the fixture is IC-rated before covering.
3. Plumbing and wiring penetrations: seal around all pipes, conduit, and cable runs through the ceiling drywall with canned spray foam or acoustical sealant.
4. Attic hatch: the attic hatch itself often has no weatherstripping and no insulation. Add adhesive foam weatherstrip to the perimeter and attach rigid foam to the back of the hatch door to achieve at least R-10.
5. Soffit and top-plate intersections: where exterior walls meet the attic floor, the blocking between joists may be missing. Block and foam these cavities before blowing to prevent the blown material from falling into the wall cavity below.

IRC N1102.4 ↗ covers building thermal envelope air-barrier requirements. Local inspectors increasingly require a blower-door test to verify air-sealing quality in new construction and permitted renovation work.

Ventilation Clearance: Don't Block the Soffit Path

Vented attic designs require an unobstructed airway from soffit vents to ridge or gable vents. Before blowing, install rigid rafter baffles (also called vent chutes or insulation dams) at each rafter bay where it meets the eave. These maintain a minimum 1-inch airway above the insulation surface. IRC §R806.3 ↗ specifies minimum ventilation ratios for vented attic assemblies (1:150 of attic floor area, or 1:300 with cross-ventilation). Without baffles, blown material can cover soffit vents, causing moisture buildup and premature roof sheathing decay.

Climate Zone Considerations for Blown-In Insulation

Blown-in insulation requirements vary by climate zone under the IECC energy code. Two code sections are most relevant for DIY attic and wall projects.

Ventilation ratio variance ( IRC §R806.3 ↗ ): The 1:150 ventilation ratio (net free vent area to attic floor area) drops to 1:300 when at least 40% of the required ventilation is provided at the ridge and 60% at the soffit. Climate Zone 6–8 jurisdictions often require the more conservative 1:150 ratio regardless of vent placement because cold-climate moisture loads are higher. Whether your jurisdiction allows 1:300 depends on the IRC edition your state or municipality has adopted.

Vapor retarder requirement (IRC N1102.4 ↗): For Climate Zones 4 through 8, a Class II vapor retarder (perm rating 0.1–1.0) is required per IECC N1102.4 where the insulation assembly is in direct contact with the conditioned ceiling plane. Blown cellulose in an open attic floor (above the ceiling drywall, not in a cathedral assembly) generally does not require an additional vapor retarder layer because the ceiling drywall itself provides Class III vapor control. However, if you are insulating a cathedral ceiling or unvented roof assembly in Zones 4–8, consult a contractor — the vapor retarder position and type are jurisdiction-specific.

Climate Zones 1–3 (most of Florida, Texas, Arizona, Gulf Coast) do not require a Class II vapor retarder for attic floor assemblies. The dominant moisture risk in these zones is humid outdoor air entering the attic, not interior vapor drive — a vapor retarder on the ceiling plane could trap moisture and cause condensation.

Jurisdiction note: requirements vary by climate zone and by the specific IECC edition adopted by your state or municipality. This content reflects the 2021 IECC. Depending on your jurisdiction, an earlier edition (2018, 2015) or a state-specific energy code may apply. Confirm all ventilation and vapor retarder requirements with your local building authority before installation.

Estimates only — verify with your local building authority and a licensed insulation contractor before construction. See our full disclaimer.