Attic Insulation Calculator

Calculate the insulation needed to reach a target R-value, its installed cost, and a rough yearly energy saving.

By Konstantin Iakovlev · Updated September 2026 · Source: ENERGY STAR — Recommended Home Insulation R-Values (retrofit table based on the 2021 IECC)

Estimated Cost

$3,648.00

Annual Savings

$144.83/yr

Payback Period

25.2 years

Insulation Details

R-Value to AddR-38
Inches Needed~11.9"
Material Cost$2,280.00
Total Installed$3,648.00
Heating (gas furnace)$116.72/yr
Cooling (central air)$28.11/yr
Est. Energy Savings$144.83/yr

Use the Attic Insulation Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only. Results are estimates from the numbers you enter and the assumptions described on this page; check them against local building codes, product specifications and current prices, and have structural, electrical or gas work designed or checked by a licensed professional.

How It Works

This calculator works out how much insulation it takes to bring an attic from its current R-value up to a target, what that costs and roughly what it saves. ENERGY STAR's retrofit table, based on the 2021 International Energy Conservation Code, sets the target for an uninsulated attic at R-30 in climate zone 1, R-49 in zones 2 and 3 and R-60 in zones 4 through 8; with 3 to 4 inches already in place it recommends adding R-25, R-38 and R-49.

The R-value to add is the target minus what you have now, and the depth is that figure divided by R per inch: 3.2 for blown-in cellulose, 3.7 for fiberglass batts and 6.5 for spray foam. Material is priced at $1.50 per square foot for cellulose, $1.20 for batts and $3.50 for spray foam for every R-30 added, and labor adds 60% on top. Savings follow the heat that stops flowing through the ceiling: square feet × (1/R before − 1/R after) × degree-days × 24 hours, with about R-2 of drywall and air films added to both R-values. Heating is priced for a 90%-efficient gas furnace at $1.48 a therm (EIA's 2025 residential average) and cooling for a SEER 14 air conditioner at 18.34¢ per kWh (EIA, June 2026), using rounded degree-days of 1,800 heating and 2,400 cooling for zones 1-3, 4,300 and 1,300 for zone 4, and 6,800 and 600 for zones 5-8. Because heat flow falls with 1/R, the first inches do most of the work: in zone 4, bringing a bare 1,500 sq ft attic to R-49 saves about $1,517 a year, while topping up the same attic from R-19 saves $88. The method ignores sunshine and the heat from people and appliances, so real heating savings usually run somewhat lower, and a heat pump or electric heat changes the price of each unit saved.

Sealing air leaks should come first, because warm air pouring through gaps will undercut even a deep blanket of insulation. There's also a ceiling to the gains: past a certain R-value the payback shrinks, and that threshold depends on your climate zone. Check your local building code for the minimum R-value required where you live before settling on a number.

Example: Upgrading Insulation in a 1,500 sq ft Attic

  1. 1 Input: a 1,500 sq ft attic at R-19 today, a target of R-49 and blown-in cellulose.
  2. 2 R-value to add: 49 − 19 = R-30. Depth: 30 ÷ 3.2 per inch = about 9.4 inches of cellulose.
  3. 3 Cost: material 1,500 × $1.50 × (30 ÷ 30) = $2,250, and labor at 60% adds $1,350, for $3,600 installed.
  4. 4 Savings in zone 4: 1,500 × (1/21 − 1/51) = 42.0 Btu per hour per °F. Heating: 42.0 × 4,300 degree-days × 24 ÷ 0.9 = 48.2 therms × $1.48 = $71.31; cooling: 42.0 × 1,300 × 24 ÷ 14,000 = 93.6 kWh × $0.1834 = $17.17. Total $88.48 a year, so the $3,600 takes about 41 years to pay back (30 years in zones 5-8, where the heating share is larger). Taking a bare attic to R-49 instead costs $5,880 and saves about $1,517 a year, a payback of about 4 years.

Source: ENERGY STAR — Recommended Home Insulation R-Values (retrofit table based on the 2021 IECC) · Last updated: September 2026

Frequently Asked Questions

How much insulation do I need in my attic?
ENERGY STAR's retrofit table, based on the 2021 International Energy Conservation Code, recommends R-30 for an uninsulated attic in climate zone 1, R-49 in zones 2 and 3 and R-60 in zones 4 through 8. At the calculator's R-3.2 per inch for blown cellulose, R-49 is about 15 inches and R-60 about 19; fiberglass batts at R-3.7 per inch need about 13 and 16 inches. Check your current insulation depth and add enough to reach the target.
What is the payback period for adding attic insulation?
Divide the installed cost by the yearly savings, and the starting point decides it. In the calculator's zone 4 setting, taking a bare 1,500 sq ft attic to R-49 costs about $5,880 installed in cellulose and saves about $1,517 a year, a payback of about 4 years; topping up the same attic from R-19 costs $3,600 and saves about $88 a year, roughly 41 years. ENERGY STAR estimates that air sealing and adding insulation saves an average of 15% on heating and cooling costs. The 25C energy tax credit that covered 30% of insulation costs (up to a $1,200 annual limit) expired December 31, 2025, so 2026 projects depend on state and utility rebates.
Should I use blown-in or batt insulation for my attic?
Blown-in insulation is generally better for attics because it fills gaps and irregular spaces more completely. It is also faster and cheaper to install over existing insulation. Batts work well in uninsulated attics with standard joist spacing and no obstructions.

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