Attic insulation has one of the fastest paybacks of any home improvement. A properly insulated attic can cut heating and cooling costs by 10 to 50 percent depending on what is there now. If your attic has less than 6 inches of insulation or is missing it entirely, the project pays for itself faster than most homeowners expect.
Here is what it actually costs and how to figure out what makes sense for your situation.
The three main attic insulation options
Blown cellulose is the best value for most DIY attic projects. Made from recycled paper with fire retardant treatment, it provides R-3.7 per inch and fills gaps and irregular spaces well. A blowing machine rental is usually free with a minimum bag purchase at hardware stores.
Blown fiberglass is slightly easier to work with in very humid attics because it does not absorb moisture. It provides R-2.5 per inch, which means you need more depth than cellulose to reach the same R-value. Costs roughly the same as cellulose per square foot of coverage.
Spray foam is significantly more expensive and is rarely the right choice for an open attic floor. It is useful for sealing the underside of the roof deck in conditioned attic spaces, but for standard attic floor insulation, blown insulation outperforms it on cost.
Material costs for a 1,000 square foot attic
These are material-only costs for a DIY project starting from R-0 (uninsulated):
| Target R-value | Blown cellulose | Blown fiberglass |
|---|---|---|
| R-19 | $120 to $150 | $180 to $220 |
| R-30 | $200 to $250 | $290 to $360 |
| R-38 | $250 to $310 | $365 to $460 |
| R-49 | $320 to $400 | $470 to $580 |
Bag prices vary by region and supplier. Check current prices at your local hardware store and use the bag count from the coverage chart on the bag itself to verify your total.
Professional installation costs
Hiring an insulation contractor adds $0.50 to $1.50 per square foot for labor, depending on your region and how accessible the attic is. Most attics are easy to blow and fall on the lower end.
For a 1,000 square foot attic to R-38 with blown cellulose:
- Materials: $250 to $310
- Labor: $500 to $1,500
- Total professional install: $750 to $1,800
For a 1,500 square foot attic:
- Total professional install: approximately $1,200 to $2,600
Machine rental for DIY is typically free with purchase of 10 or more bags. Most 1,000 square foot projects to R-38 need 48 to 55 bags of cellulose, well above the free rental threshold.
Adding insulation over existing insulation
If your attic already has some insulation, you do not need to remove it. Measure the existing depth, identify the material type, and calculate the existing R-value. Then calculate only the additional insulation needed to reach your target.
For example: 3 inches of old fiberglass batts (about R-10) in a 1,200 square foot attic. Target is R-49.
- Additional R-value needed: 49 minus 10 = R-39
- Blown cellulose depth for R-39: 39 / 3.7 = 10.5 inches
- Material needed for 1,200 sq ft at 10.5 inches: about 58 bags
The attic insulation calculator handles this automatically. Enter the area, existing depth and material, and target R-value, and it calculates exactly the bags and cost for just the additional insulation.
What to do before you add insulation
Air sealing before insulating matters more than the insulation itself per dollar spent. Heat escapes primarily through gaps, not through the insulation material. The biggest gaps in most attics:
- Top plates of interior partition walls (visible as gaps between ceiling drywall and attic floor)
- Gaps around plumbing stacks and electrical penetrations
- Recessed light fixtures (which must be IC-rated or covered before insulating over them)
- Attic hatch or pull-down stair
Seal these with rigid foam and acoustic sealant before blowing. An hour of air sealing is worth more than another couple inches of insulation.
Payback time
In a poorly insulated house in a climate with real heating and cooling demand (cold winters or hot summers), attic insulation typically pays back in 3 to 7 years in energy cost savings. The US Department of Energy estimates 15 percent reduction in total energy costs as a typical result for homes with inadequate attic insulation going to code levels.
At $200 per month in heating and cooling costs, 15 percent savings is $30 per month or $360 per year. A $900 insulation project pays back in 2.5 years. These are rough estimates, but the order of magnitude is consistently favorable in most US climates.
Use the attic insulation calculator to get a precise bag count and cost for your attic dimensions and current insulation level. For blown-in insulation specifically, the blown-in insulation calculator includes depth, bag count, and cost for cellulose and fiberglass options.
Frequently Asked Questions
Is blown cellulose or blown fiberglass better for attics?
Cellulose is usually the better choice. It provides more R-value per inch (R-3.7 vs R-2.5 for fiberglass), costs about the same per bag, and settles less over time. Fiberglass has one advantage: it does not absorb moisture, so it is preferred in attics with known humidity issues or in very humid climates. For most homeowners in most climates, cellulose is the better value.
Do I need to remove old insulation before blowing in new?
No, in most cases. Blow new insulation directly over existing material, whatever type it is, as long as it is dry and free of mold. The only exceptions are wet or contaminated insulation, and old vermiculite insulation (used in homes built before 1980), which may contain asbestos and requires professional testing and removal. Dry, older batts or loose fill can simply be covered.
How long does it take to blow in attic insulation?
Most attic projects take 4 to 8 hours for a DIY job, including setting up baffles and sealing penetrations. A professional crew can complete a 1,000 to 1,500 square foot attic in 2 to 4 hours. The blowing itself goes fast; the preparation work (baffles, air sealing, marking depth guides) takes the most time and matters the most for the final result.
What R-value does code require for my attic?
It depends on your climate zone. The 2021 International Energy Conservation Code requires R-38 in climate zones 1 through 4 (most of the southern half of the US) and R-49 in zones 5 through 8 (the northern half, mountain states, and Alaska). Some local codes are stricter than the IECC minimums. Check with your local building department if you are doing permitted work.
Does attic insulation actually reduce cooling costs?
Yes. The attic floor is where heat transfers most directly between the living space and the super-heated attic air above. Studies by the Oak Ridge National Laboratory found that bringing an under-insulated attic to code levels reduces heating and cooling costs by 10 to 15 percent on average, and by more in homes with very little existing insulation. The savings are most noticeable in summer in warm climates and in winter in cold climates.
Is blowing in attic insulation a good DIY project?
It is one of the more accessible home improvement projects for a motivated homeowner. The equipment is simple: a rental blower, hoses, and bags of insulation. The physical demands are moderate: you are mostly working from above the floor joists in a hot, cramped space. The main risks are inadequate air sealing before blowing (leaving gaps that insulation does not fill), and covering can lights that are not rated for insulation contact. Both are avoidable with proper preparation.