Attic insulation calculator

Attic insulation cost

The single highest-return insulation project in almost every US home. Heat rises, and an under-insulated attic bleeds it straight through the roof.

Insulating 1,200 square feet of attic from R-19 to the zone 4 recommendation of R-49 costs $2,370 to $3,200 installed at national-average rates, roughly $2.32 per square foot, and saving about $63 a year. Your climate zone changes the target substantially: the same assembly needs R-38 in zone 2 and R-49 in zone 6, so the same house costs meaningfully more to bring up to standard in the north.

Priority: Start here. In nearly every climate zone the attic returns more per dollar than any other assembly, and it is the easiest to access.

How much attic insulation do you need?

Work from the gap rather than the area. Take your zone's target, R-49 for attic insulation in zone 4, subtract the R-value already in place, and divide what is left by the material's R per inch. Closing an R-30 gap takes 8.6 inches of blown-in cellulose, 9.4 inches of fiberglass batt or 4.6 inches of closed-cell foam.

Turning depth into material is the last step. Blown-in is sold by the bag against a coverage chart that falls as depth rises, one bag covers 32 square feet at R-30 but only about 20 at R-49, so 1,200 square feet at R-49 works out to roughly 62 bags. Batts are sold by the package at 40 to 49 square feet each, and rigid foam in 32-square-foot sheets.

Enter your square feet in the calculator above and it does all of this from your state, the zone lookup, the target, the gap, the depth and the installed cost, without an email address or a signup.

Best insulation material for attic

Not every material suits every assembly. For attic, the realistic options are fiberglass batt, blown-in fiberglass, blown-in cellulose, open-cell spray foam, closed-cell spray foam.

Fiberglass Batt delivers R-3.2 per inch at about $0.15 per square foot per inch, which puts this job at $2,456. Cheapest material per R-value and available everywhere, though performance collapses if compressed or poorly fitted. It is realistically DIY-installable.

Blown-In Fiberglass delivers R-2.5 per inch at about $0.12 per square foot per inch, which puts this job at $3,101. Fills irregular cavities and around obstructions well, though lowest r per inch of any option, so it needs real depth. It is realistically DIY-installable.

Blown-In Cellulose delivers R-3.5 per inch at about $0.14 per square foot per inch, which puts this job at $2,784. Best R per inch of the affordable materials, though settles roughly 10-20% over time unless dense-packed. It is realistically DIY-installable.

R-value per inch matters most when depth is constrained. In an open attic you can simply add depth, so cost per R-value wins. In a 2x4 wall cavity or a shallow crawl space you have a fixed 3.5 inches to work with, and closed-cell spray foam's R-6.5 per inch is the only way to reach a high target, which is exactly why it costs what it does.

Blown-in, batt or spray foam in an attic

An open attic floor is the one place in the house where depth is nearly free, which changes the material calculation completely. Cost per R-value wins, and that points at blown-in cellulose or fiberglass batt: $2,784 and $2,456 respectively for the reference job above, against $9,471 for closed-cell spray foam.

Between the two cheap options, installation quality decides it. Batts are cheaper to fit in clean, evenly spaced joist bays and lose most of their rated performance when compressed or gapped around wiring and boxes, failures that are extremely common in real installations. Run the blown in insulation calculator setting instead and the material flows around every obstruction, which is why it dominates attic retrofits. Cellulose settles roughly 10-20% over the first few years unless dense-packed, so installers blow slightly deep to allow for it.

Two installation details matter more than the product choice. Baffles at the eaves keep material off the soffit vents, because blocking that airflow is how a well-insulated attic ends up with a damp roof deck. And air seal the ceiling plane first, around plumbing stacks, recessed lights, the attic hatch and duct penetrations, because insulation laid over unsealed bypasses hides them rather than fixing them.

Can you do this yourself?

Labor is 40-60% of a professional insulation job, so it is the largest single saving on the table: the reference job above drops from $2,784 installed to about $1,704 doing it yourself, including a $120 allowance for blower rental and protective equipment. Most suppliers lend the blower free with a material purchase, which is why blown-in is the most DIY-friendly option despite needing a machine.

Spray foam is the exception and it is not a close call. Professional equipment costs more than the job, and the chemistry is unforgiving of mistakes in mix ratio and substrate temperature. Badly applied foam either fails to cure or shrinks away from the framing, and both are expensive to remove. Kit foam from a big-box store is fine for rim joists and small patches, not for an assembly.

Whatever you use, budget for a respirator, sealed eye protection and long sleeves, work off boards rather than the ceiling drywall, and do the air sealing before the insulation goes down. Once the material is in place you will not want to move it again to find the leaks.

How we calculated these estimates

Every figure on this page comes from the same open formula the calculator above uses. We start from your state's DOE climate zone, look up the R-value the Department of Energy recommends for the assembly you are insulating, subtract the R-value already in place, and price only the gap that is left, which is why two houses of identical size get very different numbers. Depth comes from the material's published R per inch, material cost from a 2026 national baseline per square foot per inch, and a 10% allowance is added for trimming and irregular framing. Installed labor is then scaled by the construction earnings multiplier the Bureau of Labor Statistics publishes for your state. The energy saving is a steady-state conduction estimate priced against real US Energy Information Administration residential electricity rates and a national natural gas price, with a 70% realization factor applied. It deliberately excludes air leakage, duct losses and solar gain, so it is a conservative planning figure rather than an energy audit. Nothing is hidden behind a lead form and no contractor pays to appear here. What this is not is a quote: attic access, obstructions, existing damage and any air sealing or venting work are priced separately by whoever does the job.