See what it costs to bring your attic up to the recommended R-value with blown-in fiberglass or cellulose, including the number of bags if you DIY. Prices updated October 2026.

What your estimate means

The calculator works out how much R-value your attic is missing. That’s the ENERGY STAR target for your climate zone minus what your current insulation provides. It then reads the number of bags needed for that added R-value straight from the manufacturer’s bag label. Bags are what you pay for, whether you blow it yourself or hire it out.

The contractor estimate is the bag cost plus typical installation labor, with a minimum job charge for small attics. The DIY estimate is the bags at retail price plus basic safety gear. Most stores lend the blowing machine free when you buy 10 or more bags.

How to use this calculator

Choose fiberglass or cellulose. Both blow in the same way. Cellulose bags cost less each, but you need more of them.
Enter your attic floor area. For a simple house, it’s the length × width of the floor below.
Pick your climate zone. This sets the recommended total R-value. If your local code or energy program asks for a different number, choose “Custom”.
Describe what’s already there. Pick the type and measure the depth. Blown-in insulation can go right on top of old batts or loose fill if it’s dry and clean.
Add extras if needed: baffles to keep soffit vents clear, air sealing, or removal of damaged insulation.

How the cost is calculated

Existing R  = Existing depth × R per inch (by type)
R to add    = Target R − Existing R
Bags        = label bags per 1,000 sq ft at that R × Area ÷ 1,000 × (1 + extra %)
Contractor  = max(Bags × bag price + Area × labor rate, job minimum) + extras
DIY         = Bags × bag price + safety gear + extras

Bag counts and minimum depths come from the manufacturers’ coverage charts. These are the reference products we use (we’re not affiliated with either):

Target R	Fiberglass bags / 1,000 sq ft	Fiberglass depth	Cellulose bags / 1,000 sq ft	Cellulose depth
R-30	14.6 ($0.83/sq ft)	10.8"	36.5 ($0.58/sq ft)	8.9"
R-38	19.0 ($1.08/sq ft)	13.5"	50.1 ($0.80/sq ft)	11.2"
R-49	25.0 ($1.43/sq ft)	17.0"	68.5 ($1.09/sq ft)	14.3"
R-60	31.5 ($1.80/sq ft)	20.5"	83.5 ($1.33/sq ft)	17.3"

Fiberglass: Owens Corning AttiCat (27.5 lb bag). Cellulose: Greenfiber Sanctuary (25 lb bag). Material cost per sq ft uses average bag prices of $57.00 and $15.97.

Existing insulation R per inch: batts 3.0, loose fiberglass 2.5, cellulose 3.4, rock wool 3.3. These are conservative, because old insulation settles and compresses.
Labor: $0.50–$1.30 per sq ft. Minimum job: $500–$2,000.
Extras: baffles $2.00–$3.00 each, air sealing $350–$3,000, removal $1.00–$2.00 per sq ft.

Contractors often buy material in bulk and blow commercial-grade products, so real quotes, especially for fiberglass, can come in below the bag-based estimate. See the methodology page for the full details.

Worked example: topping up an older attic

A 1,200 sq ft attic in climate zone 5 has 3½" of old fiberglass batts. The owner plans to blow cellulose on top:

Existing: 3.5" × 3.0 = R-10.5. Target for zone 5: R-60. So add R-49.5, about 14.4" of cellulose.
Bags: 88 (label chart plus 5% for obstructions). That’s enough for the free blower rental.
DIY: about $1,475 including safety gear (range $1,226–$2,044)
Contractor: about $2,485 (range $1,794–$3,496), or $2.07 per sq ft

Blowing it yourself saves around $1,010, for a day’s work with a helper feeding the machine. If the attic needs air sealing first, that’s the step most worth paying for.

Attic insulation cost by size

Topping up 3½" of old batts. Contractor prices at average rates, with ranges.

Attic	Fiberglass to R-49	Cellulose to R-49	Cellulose to R-60	DIY cellulose to R-49
800 sq ft	$1,689 $1,321–$2,200	$1,407 $984–$2,000	$1,662 $1,201–$2,338	$757 43 bags
1,000 sq ft	$2,097 $1,637–$2,733	$1,762 $1,233–$2,488	$2,066 $1,491–$2,906	$932 54 bags
1,500 sq ft	$3,117 $2,429–$4,065	$2,644 $1,849–$3,732	$3,091 $2,229–$4,348	$1,364 81 bags
2,000 sq ft	$4,137 $3,220–$5,397	$3,525 $2,466–$4,976	$4,132 $2,981–$5,812	$1,795 108 bags

Recommended attic R-value by climate zone

ENERGY STAR’s recommendations for existing homes, based on the 2021 International Energy Conservation Code:

Climate zone	Uninsulated attic	Already has 3–4" of insulation
1	R-30	Add R-25
2–3	R-49	Add R-38
4–8	R-60	Add R-49

Not sure of your zone? Most of the Deep South is zone 2–3, the middle of the country is zone 4, and the northern tier of states is zone 5–7.

Fiberglass vs. cellulose

Cellulose is denser and gives a higher R-value per inch, so the same R-value is thinner. It also blocks air movement through the insulation better. Bags are cheap, but you need about 2½ times as many.
Fiberglass is lighter, so there’s less weight on old ceilings. It doesn’t absorb water, and it’s less dusty to blow. It needs more depth for the same R-value, so check that you have room below the roof at the eaves.
For per-square-foot comparisons with batts and spray foam, attic insulation typically runs $1–$4 per sq ft installed, according to HomeGuide. Spray foam on the roofline is the priciest. Estimate it with the spray foam cost calculator.

Frequently asked questions

How much does it cost to insulate a 1,000 sq ft attic?

Topping up older insulation to R-49 runs about $1,762 with a contractor using cellulose, or $2,097 with fiberglass. Doing it yourself costs about $932 in cellulose bags and gear.

How many bags of blown-in insulation do I need?

Read it from the bag label’s coverage chart. For 1,000 sq ft at R-38, that’s about 19 bags of Owens Corning AttiCat (27.5 lb bag) or 50 bags of Greenfiber Sanctuary (25 lb bag). Adding on top of existing insulation needs fewer. The calculator does this for you.

Can I put new insulation on top of old?

Yes, if the old insulation is dry and free of mold, pests and odors. Remove it if it’s wet, moldy, or contaminated. If it looks like gray-brown pebbles (vermiculite), don’t disturb it. It may contain asbestos, so have it tested.

Is it cheaper to blow in insulation yourself?

Usually, yes. Labor is roughly $0.50–$1.30 per sq ft, and stores lend the blower free with 10+ bags. The job takes two people, one feeding the machine and one in the attic, plus a mask and goggles.

Should I air seal before adding insulation?

Yes. Air leaking up through gaps around lights, pipes and top plates carries heat and moisture straight through insulation. Sealing those first is one of the most cost-effective energy upgrades, and it can only be done easily before the new insulation goes in.

How much does attic insulation save?

HomeGuide puts typical savings at 10–20% of heating and cooling costs, depending on climate and how little insulation you started with. Attics starting from a few inches see the biggest gains.

Attic Insulation Cost Calculator