How many inches of blown-in does your attic need?
Measure what you have, pick your climate, and get three numbers: the R-value to target, the inches of loose fill that closes the gap, and what the top-up should cost before rebates.
Cost uses published national per-square-foot ranges for blown-in cellulose. Assumption: a top-up over sound existing insulation prices near the low half of the published range; a near-empty attic uses the full range. Air sealing is quoted separately (see below).
Stated assumptions: blown cellulose ≈ 3.2–3.8 R per inch, blown fiberglass ≈ 2.2–2.7, batts ≈ 3.1; zone targets follow DOE/ENERGY STAR guidance (R-30–R-49 hot through R-49–R-60 cold, R-60 subarctic).
Keep this result with your project. It becomes part of Your Retrofit Plan.
We use this only to save your result. Create a free account with the same email and it appears in your plan.
What's next
A five-minute check tells you what you have
You do not need a professional to get the input this calculator needs. A ruler and a flashlight through the attic hatch will do it.
Ruler through the hatch
Push a ruler or tape straight down to the drywall in a few spots and read the depth. Measure away from the hatch itself, which is usually the thinnest spot.
Can you see joists?
If the wood framing is visible above the insulation, you are at roughly R-13 or less. That is well under target in every climate zone and the strongest signal a top-up will pay off.
Check for patchiness
Wind-scoured corners, trampled walkways, and bare spots around fixtures matter as much as average depth. Use your thinnest common reading, not your best one.
Why the answer is a range, not a number
Northern climates call for R-49 to R-60 on the attic floor, and hotter zones a bit less. Anywhere inside the band is a good outcome: heat loss drops steeply with the first inches and flattens out near the top of the range, so each inch past R-60 buys very little. That is also why topping up almost always beats tearing out. Sound existing insulation keeps counting toward the target, and you only pay for the gap. The theory behind the targets, and the common installation mistakes, are covered in our attic insulation guide, and the material trade-offs in the blown-in cellulose guide.
Air seal before you blow
This is the step manufacturer coverage calculators never mention, and it decides whether your new inches perform as rated.
Every attic floor has bypasses: top plates, plumbing and wiring penetrations, chases, recessed lights, the hatch itself. Blow new insulation over them and the leaks keep running underneath, except now they are buried under a foot of loose fill and much more expensive to reach. Seal first, then insulate. Professional whole-home air sealing typically runs $1,000–$4,000 depending on size and leak density, and it is often bundled into insulation quotes, so ask for it as a line item. The full ordering logic is in the retrofit sequencing guide.
What an attic top-up costs
National installed ranges, materials plus labor, before rebates.
| Material | Installed, per sq ft |
|---|---|
| Blown-in cellulose | $0.60–$2.30 |
| Blown-in fiberglass | $0.50–$2.00 |
| Fiberglass batts (sources disagree) | $0.90–$1.80 vs $2–$4 |
For a typical 1,000 sq ft attic that means roughly $800–$2,500 with blown-in cellulose, and $900–$3,600 for blown-in attic work generally. Easy access and a straight top-up sit near the low end; removal, baffles, and deep R-60 targets push high. The full breakdown of price drivers lives in the attic insulation cost guide, and when you are ready for real numbers, get quotes from insulation contractors who work your area.
Weatherization is the most subsidized work in the business
Many state and utility efficiency programs cover a large share of insulation and air sealing, in the strongest programs most of the bill. Where states have launched the federal HEAR rebate program, income-eligible households can get up to $1,600 toward insulation, air sealing, and ventilation, but rollout is state by state and several big states have not launched yet, so treat that figure as location-dependent. The old 25C federal tax credit for insulation expired for installations after 2025, so ignore any page still advertising it. The calculator above shows before-rebate prices; match your rebates to see your real number, and check your state page for program specifics.
Attic depth and R-value questions
How many inches of blown-in insulation do I need?
It depends on your climate and what is already up there. Northern homes generally target R-49 to R-60, which works out to roughly 13 to 19 inches of loose-fill cellulose from bare framing (cellulose runs about 3.2 to 3.8 R per inch). Blown fiberglass delivers less R per inch, so the same target takes roughly 18 to 27 inches. If you already have a few inches of sound insulation, you only need to close the gap.
What R-value do I need for my attic?
DOE and ENERGY STAR guidance runs from about R-30 to R-49 in hot climates up to R-49 to R-60 in cold, northern climates. The target is a band, not a single number: anywhere inside it puts you in good shape, and each inch past the top of the band saves noticeably less than the one before it.
Can you put new insulation over old?
Usually, yes. As long as the existing material is dry, uncompressed, and not contaminated, blowing loose fill directly over it is standard practice, and cellulose over old fiberglass is a common combination. The one non-negotiable step first: air seal the attic floor, because new insulation buries the leaks and makes them much harder to fix later.
How much does it cost to insulate a 1,000 sq ft attic?
Published national ranges put a 1,000 sq ft attic at roughly $800 to $2,500 for blown-in cellulose, and $900 to $3,600 for blown-in attic work generally. Topping up an accessible attic sits near the low end. Removal of old material, deep R-60 targets, and bundled air sealing push toward the high end, before rebates.
Do I need to remove old insulation first?
Only when there is a real problem: wet or moldy material, pest contamination, or live knob-and-tube wiring that cannot be buried. Otherwise removal is wasted money, since sound existing insulation still counts toward your target. When removal is needed, it adds real cost, so make sure any quote itemizes it.
Get alerts when insulation rebates change in your state
Free weekly digest. Unsubscribe anytime. Privacy policy.
See what your state pays toward attic insulation.
You have your inches. Now cut the price: insulation and air sealing rebates are the most generous around, and matching takes two minutes.
Match my rebates