Blown-in insulation costs about $0.90 to $2.40 per square foot installed, or roughly $1,000 to $2,500 to bring a typical 1,000 square foot attic up to code. Loose fiberglass or cellulose is machine-blown across the attic floor to a target R-value, usually R-38 to R-60 depending on climate zone. A confident DIYer can cut the cash cost to $600 to $1,100 with a rented blower, but the trade-off is coverage consistency, air sealing, and getting the ventilation baffles right so the new insulation does not choke your roof.
This guide breaks down real 2026 pricing, R-value math by material, the DIY-versus-pro decision, and the one thing most cost guides skip: how blown-in insulation interacts with your roof deck and attic ventilation. Get that part wrong and you trade a lower energy bill for a moisture problem.
How much does blown-in insulation cost in 2026?
Blown-in attic insulation runs $0.90 to $2.40 per square foot installed, with most homeowners paying between $1,000 and $2,500 for a standard attic. National averages cluster near $1,600 for a mid-size job. Price swings with material, target R-value, attic access, and whether the crew also air-seals and adds ventilation baffles before blowing.
Fiberglass and cellulose are the two common materials, and cellulose usually costs slightly less per bag while fiberglass resists moisture better. The table below shows typical installed pricing by material and the raw material cost if you buy bags yourself.
| Material | Installed cost / sq ft | Material only / sq ft | R-value per inch |
|---|---|---|---|
| Blown fiberglass | $1.00 to $2.80 | $0.50 to $1.50 | R-2.5 to R-4.0 |
| Blown cellulose | $0.60 to $2.30 | $0.60 to $1.00 | R-3.2 to R-3.8 |
| Blown rock wool | $1.40 to $2.10 | $1.00 to $1.60 | R-3.0 to R-3.3 |
Attic size drives the total. The next table estimates installed cost to reach R-49, a common target across much of the country, using mid-range fiberglass pricing.
| Attic floor area | Typical installed cost (R-49) |
|---|---|
| 500 sq ft | $700 to $1,300 |
| 1,000 sq ft | $1,200 to $2,500 |
| 1,500 sq ft | $1,800 to $3,600 |
| 2,000 sq ft | $2,400 to $4,800 |
What R-value do you need, and how thick is that?
Most U.S. attics need R-38 to R-49, and the coldest climate zones call for up to R-60. R-value measures resistance to heat flow, so higher is better in both winter and summer. The Department of Energy publishes recommended attic R-values by climate zone through Energy Star, and many local codes set a minimum for insulation work that requires a permit.
R-value converts to a physical depth based on the material. Because fiberglass and cellulose deliver different R per inch, the same R-49 target lands at different fill depths. Blow to the higher end of the depth range so the insulation still hits target after it settles.
| Target R-value | Fiberglass depth | Cellulose depth | Common climate zones |
|---|---|---|---|
| R-38 | 10 to 14 in | 10 to 12 in | Zones 2 to 3 (South) |
| R-49 | 14 to 18 in | 13 to 16 in | Zones 4 to 5 (Mid, Mountain) |
| R-60 | 18 to 22 in | 16 to 20 in | Zones 6 to 8 (North) |
How many bags of blown-in insulation do you need?
Bag count depends on your square footage and target R-value, because coverage per bag drops sharply as depth rises. One bag of blown fiberglass covers roughly 38 square feet at R-49 and only about 30 square feet at R-60. Every bag prints a coverage chart on the label, so use that number for your exact product rather than a generic estimate.
To size a job, divide attic square footage by the per-bag coverage at your target R-value, then add 10 to 15 percent for settling, irregular framing, and fill around ducts and HVAC equipment.
| Target R-value | Fiberglass coverage / bag |
|---|---|
| R-13 | ~162 sq ft |
| R-19 | ~109 sq ft |
| R-30 | ~66 sq ft |
| R-49 | ~38 sq ft |
| R-60 | ~30 sq ft |
Example: a 1,000 square foot attic at R-49 needs about 1,000 divided by 38, or roughly 27 bags, plus 3 to 4 extra for settling, so plan on 30 to 31 bags.
Fiberglass vs cellulose: which blown-in material is better?
Fiberglass and cellulose both work well; the right pick depends on moisture, budget, and fill needs. Fiberglass does not absorb water and will not settle much, which suits humid or leak-prone attics. Cellulose packs denser, fills around wires and obstructions better, and usually costs a little less, but it can absorb water and settle over time, shaving effective R-value if it gets wet or was under-filled.
| Factor | Blown fiberglass | Blown cellulose |
|---|---|---|
| R-value per inch | R-2.5 to R-4.0 | R-3.2 to R-3.8 |
| Moisture behavior | Does not absorb water | Absorbs water, risks mold if wet |
| Settling | Minimal | Settles up to ~20% |
| Fill around obstructions | Good | Excellent |
| Relative cost | Often slightly higher | Often slightly lower |
| Fire behavior | Naturally noncombustible | Treated with fire retardant |
For most attics in humid or mixed climates, fiberglass is the safer default because it shrugs off the occasional roof leak or condensation event. In dry climates or tight, wire-cluttered attics, cellulose earns its place.
DIY vs pro: which makes sense for you?
DIY blown-in insulation makes sense in an open, accessible attic with standard joists and no complications. Expect to spend $600 to $1,100 on bags plus a blower rental, versus $1,200 to $2,500 for a pro on the same 1,000 square foot attic. The pro price buys air sealing, depth verification, ventilation baffles, and cleanup that a rental machine and a Saturday do not guarantee.
Blower rental runs $50 to $100 per day and is often free with a minimum bag purchase, usually 10 to 20 bags, at major home centers. The machine is a two-person job: one feeds bags into the hopper, one runs the hose in the attic.
The table below is the honest trade-off, including a cost that most guides leave out: uneven DIY coverage lowers your effective R-value even when the average depth looks right.
| Line item | DIY | Professional |
|---|---|---|
| Cash cost (1,000 sq ft, R-49) | $600 to $1,100 | $1,200 to $2,500 |
| Blower | Rental $50 to $100/day | Included, higher pressure |
| Air sealing before blowing | Your responsibility | Usually included |
| Ventilation baffles at eaves | Buy and install yourself | Installed as prep |
| Depth consistency | Varies with skill | Verified with depth rulers |
| Effective R-value risk | Uneven fill can lose 5 to 15% | Even fill holds rated R |
When to call a pro no matter the price
Some conditions turn a DIY attic job into a hazard or a wasted weekend. Hire a professional if any of these apply:
- Knob-and-tube wiring, which can overheat under loose-fill insulation and needs evaluation first.
- Vermiculite already present, which may contain asbestos and requires testing, not disturbance.
- Existing moisture, mold, or roof leaks, which must be fixed before you bury the deck under insulation.
- Very low headroom or a complex multi-level attic where even coverage by hand is impractical.
- Significant air-sealing work around chimneys, can lights, and top plates that should happen before blowing.
How to install blown-in insulation in an attic
Blown-in installation is straightforward on paper: seal, protect airflow, then blow to depth. The order matters, because air sealing and ventilation baffles must go in before insulation covers the attic floor. Skip them and you either lose the energy savings to air leaks or trap moisture against the roof deck.
- Air-seal the attic floor. Caulk or foam the top plates, wiring penetrations, plumbing stacks, and around the chimney. Air leaks bypass insulation, so sealing first is what makes the R-value real.
- Install baffles at the eaves. Rigid vent chutes keep the new insulation from blocking soffit vents, preserving the intake side of your attic ventilation.
- Dam and protect fixtures. Build a metal or hardware-cloth barrier around non-IC-rated can lights and the attic hatch so insulation stays clear of heat sources.
- Set depth markers. Staple depth rulers to joists at several points so you can confirm the fill hits your target R-value everywhere, not just near the hose.
- Blow to target, then a bit past. Fill evenly, working back toward the hatch, and overshoot cellulose depth slightly to account for settling.
The roofing angle most cost guides skip: ventilation and ice dams
Blown-in insulation and attic ventilation are a package, not separate projects. Insulation slows heat loss into the attic; ventilation carries away the heat and moisture that still get through. Cover your soffit vents with loose fill and you cut off intake air, which can drive condensation on the roof deck and, in cold climates, feed ice dams at the eaves.
This is where a roofing lens beats a generic insulation quote. A balanced system keeps the attic cold and dry in winter so snow melts evenly instead of refreezing at the overhang. If your attic runs warm and damp after insulating, the fix is usually airflow, not more insulation. See our guide to attic ventilation and its 2026 calculation for the intake-to-exhaust math, and how soffit vents work for why baffles at the eaves are non-negotiable.
In snow country, the insulation-and-ventilation combo is your first line of defense against ice dams. Our guide to ice dam prevention methods that actually work covers how a cold, evenly vented roof deck stops the melt-refreeze cycle that no amount of gutter heat fully solves.
Is blown-in insulation worth it?
For most under-insulated attics, yes. The Department of Energy estimates that adequate insulation and air sealing can cut heating and cooling costs by up to 20 percent, and blown-in is the fastest way to add R-value over an existing attic floor without tearing anything out. It also installs over old batts, so you can top up rather than replace.
The payback stretches out if your attic is already near code or if you skip air sealing and ventilation, which are what turn rated R-value into real savings. If your roof is near end of life or you suspect a leak, sequence the roof work first. Insulating over a deck that is about to be torn off wastes the material. Our roof lifespan by material guide can help you time the two projects so you insulate once.
Frequently asked questions
How much does blown-in insulation cost per square foot?
Blown-in insulation costs about $0.90 to $2.40 per square foot installed, or roughly $1,000 to $2,500 for a typical 1,000 square foot attic. Material-only pricing for a DIY job runs $0.50 to $1.00 per square foot plus a $50 to $100 blower rental. Cellulose usually costs slightly less per bag than fiberglass, and rock wool sits at the higher end.
How many bags of blown-in insulation do I need?
Divide your attic square footage by the per-bag coverage at your target R-value, then add 10 to 15 percent for settling. One bag of fiberglass covers about 38 square feet at R-49 and 30 square feet at R-60. A 1,000 square foot attic at R-49 needs roughly 27 bags plus 3 to 4 extra. Always use the coverage chart printed on your specific bag.
Is fiberglass or cellulose better for blown-in attic insulation?
Fiberglass resists water and barely settles, making it the safer default in humid or leak-prone attics. Cellulose packs denser, fills around wires better, and usually costs a little less, but it can absorb water and settle up to 20 percent over time. Choose fiberglass for moisture resistance, cellulose for tight, wire-cluttered attics in dry climates.
Can I put new blown-in insulation over old insulation?
Yes, in most cases you can add blown-in insulation over existing batts or loose fill as long as the old material is dry and free of mold. Never cover damp or moldy insulation, and fix any roof leak first. Do not compress existing batts, since compression lowers their R-value. Air-seal the attic floor before topping up for the full benefit.
Does blown-in insulation settle over time?
Cellulose settles the most, up to about 20 percent, which is why installers blow it past the target depth so it reaches rated R-value after settling. Blown fiberglass settles very little. Buy 10 to 15 percent extra material to account for settling and irregular framing, and check depth against markers a few months after install if you used cellulose.
How thick does blown-in insulation need to be for R-49?
Reaching R-49 takes about 14 to 18 inches of blown fiberglass or 13 to 16 inches of blown cellulose, since each material delivers different R-value per inch. Blow to the higher end of the range so settling does not drop you below target. R-49 is a common requirement for climate zones 4 and 5; colder zones may require R-60.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.