Is cellulose safe and fire-resistant?

Yes. Borate treatment gives it a Class I fire rating. It chars and self-extinguishes rather than melting like fiberglass.

Dense-pack vs. loose-fill?

Loose-fill is for open attics at 1.5 lbs/cu ft ($0.80 to $1.20/sq ft). Dense-pack fills wall cavities at 3.5 lbs/cu ft ($1.50 to $2.50/sq ft).

Can I blow cellulose over fiberglass?

Yes. Cellulose fills gaps that reduce batt performance by 20 to 30%. Use our attic insulation calculator to determine the right depth when layering over existing insulation.

How many bags do I need?

At R-38, expect 25 to 30 bags per 1,000 sq ft. Each 25 lb bag covers about 40 sq ft at 3.5 inches (R-13).

Is cellulose better than fiberglass?

Cellulose offers R-3.7/inch vs. R-2.5 for blown fiberglass, fills around obstacles better, and is 85% recycled. Compare all types with our insulation calculator.

Does cellulose absorb moisture?

It can absorb up to 30% of its weight and release it. Sustained exposure from leaks will degrade performance. Proper ventilation is essential.

Which brands are best?

GreenFiber ($11 to $14/bag at Home Depot) and Nu-Wool ($14 to $17/bag, borate-only formula) are the most widely available.

InsulationCellulose Insulation Calculator

Cellulose Insulation Calculator

Q: How much does cellulose settle?

Loose-fill settles 15 to 20% in the first 1 to 2 years. Over-install by 15 to 20% to hit your target. Dense-pack settles less than 5%.

Estimate cellulose bags for loose-fill attic work or dense-pack wall cavities. The calculator keeps attic coverage charts separate from wall density assumptions.

Cellulose Plan

Application

Area (sq ft)

Target R-Value

Climate Target

Existing R-Value

Ready to calculate

Choose attic loose-fill or dense-pack wall mode.

Last updated June 3, 2026 by our expert review team

Two Cellulose Workflows

Loose-fill attic

Order from the bag coverage chart, target a minimum installed depth, and expect some settling.

Dense-pack wall

Order from cavity volume and density. A typical retrofit wall fill targets about 3.5 pcf.

Wet-spray new construction

Usually a contractor workflow. It is closer to dense-pack planning than attic loose-fill planning.

Expert Contributors

Creator

Hawkin

Certified Cost & Estimating Professional

Hawkin

Certified Cost & Estimating Professional

AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.

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Expert Review

Ehsan Ghazanfari

Licensed Structural Engineer

Ehsan Ghazanfari

Licensed Structural Engineer

FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.

See full profile

Updated June 2026

How we verify our calculators

Loose-Fill Attic vs Dense-Pack Wall

Cellulose is not one universal calculation. Attic work follows a coverage chart and installed depth. Dense-pack wall work follows cavity volume and density.

Comparison diagram showing loose-fill cellulose in an attic with settled depth markers and dense-pack cellulose in a wall cavity with a fill tube.

Use attic coverage charts for open loose-fill work. Use cavity volume and density assumptions for dense-pack wall work.

How the Calculator Works

Loose-fill attic mode

The calculator subtracts existing R-value from the target, interpolates the manufacturer-style attic coverage chart, and reports bags plus installed and settled depth.

Dense-pack wall mode

The calculator multiplies wall area by cavity depth to get volume, then uses the dense-pack density and bag weight to estimate bags.

Product label check

Cellulose labels vary by bag size, brand, and application. Treat this as a planning tool, then verify the chart printed on the bags you buy.

Reference Values

R-value: About R-3.7 per inch.
Loose-fill attic: Use the bag chart and depth markers.
Dense-pack wall: Plan around 3.5 pcf unless the installer specifies otherwise.

Pro Tips

Loose-fill attic jobs are label-chart jobs. Use the minimum bags and minimum installed depth on the product chart as the final order check.

Dense-pack wall jobs are density jobs. A typical retrofit wall fill targets about 3.5 pounds per cubic foot and usually needs professional equipment.

Air seal first when you can reach the leak. Cellulose slows air movement, but it should not be used as the only air-sealing step.

Use depth rulers in attic work. They make it easier to hit the installed depth and to check settling later.

Cellulose Planning Mistakes

Using attic math for walls

Loose-fill attic coverage is not dense-pack wall coverage. Walls need a density-based calculation.

Forgetting settled depth

Loose-fill cellulose can settle. Install to the product chart depth and check with attic rulers.

Blocking ventilation

Install baffles near soffits before loose-fill attic work so intake airflow stays open.

Burying moisture problems

Fix roof leaks, bath fan discharge, and wet insulation before adding cellulose.

Cellulose Insulation FAQ

Can I use cellulose in an attic?

Yes. Loose-fill cellulose is commonly blown across open attic floors and should be installed to the product chart depth.

Can I use loose-fill cellulose in walls?

Not loosely. Retrofit wall cavities need dense-pack installation so the material does not slump and leave gaps.

How much does cellulose settle?

Loose-fill attic cellulose can settle. Product labels account for coverage and depth, so use their minimum installed depth.

Is cellulose good for air leaks?

Dense-pack cellulose reduces air movement through cavities, but reachable air leaks should still be sealed before insulation goes in.

How is cellulose different from spray foam?

Cellulose is a recycled loose-fill or dense-pack fiber. Spray foam uses board feet, thickness, and open-cell or closed-cell chemistry. Compare foam with the spray foam calculator.

Should I compare this with attic insulation?

Yes. For a broader attic target R-value workflow, use the attic insulation calculator.

Important Disclaimer

These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.