Free Online Home Insulation Calculator
Estimate insulation material, R-value, and energy savings.
Used only to estimate savings. Enter the portion of your energy bill that this area is responsible for.
Calculation detail
These figures are rough estimates. Actual savings depend on climate, air sealing, moisture, existing insulation condition, installation quality, and future energy prices. A blower-door test and a local energy assessment are more reliable than any online estimate.
About the Home Insulation Calculator
Adding insulation is one of the most reliable ways to reduce heating and cooling costs, but the numbers on a product label are not the same as the numbers in your attic. This calculator converts a target R-value into a required thickness for common insulation types, adds a waste allowance, and estimates the material cost. It then uses a simple conduction model to estimate annual energy savings and payback, with the assumptions clearly labelled as estimates.
Understanding R-value
R-value measures thermal resistance. Higher numbers resist heat flow more effectively, so a ceiling in a cold climate may target R-49 or more while a mild climate may need less. The R-value of a cavity is not just the insulation: the assembly includes drywall, sheathing, air films, and framing. This calculator works with the added insulation only, using the difference between your current and target values. If the current value is unknown, use a conservative estimate and confirm it during a professional energy assessment.
Thickness, coverage, and cost
Each material has a different resistance per inch. Fiberglass batts are around R-3.2 per inch, blown-in cellulose around R-3.5, mineral wool around R-3.7, closed-cell spray foam around R-6.5, and rigid foam around R-5.0. To add a given R-value, divide it by the material's R-per-inch figure. The result is the installed thickness. The material area includes the waste percentage you choose, which covers cuts, framing obstructions, and small repairs. Unit costs vary widely by region and by whether you install it yourself, so replace the default with a local quote when you can.
How savings are estimated
The calculator uses the change in U-value, which is the inverse of R-value. If the current assembly is R-11 and the target is R-38, the heat flow through that area falls by a large percentage. Multiplying that percentage by the annual energy cost you attribute to the area gives a first-order savings estimate. It does not model air leakage, thermal bridging, humidity, or equipment efficiency. Air sealing often produces savings that are just as important as adding insulation, and the two measures work best together.
Frequently asked questions
Can I just add insulation on top of the old material?
Often yes, especially in an attic, but check for moisture, knob-and-tube wiring, and whether the existing material has a vapor barrier in the wrong place. Compressing some materials reduces their R-value. Follow local guidance and do not cover recessed light fixtures unless they are rated for contact with insulation.
Why is the payback different from a contractor's estimate?
Contractors may use different energy prices, climate data, air-sealing assumptions, and utility incentives. They may also include labour and air sealing in the project cost. Compare the assumptions and ask for the savings model in writing.
Does a higher R-value always save more?
Savings diminish as R-value rises because the U-value curve flattens. Going from R-11 to R-19 saves a lot; going from R-49 to R-57 saves much less for the same added thickness. The right target depends on climate, cost, and available space.