Best insulation for attics: 6 options ranked (October 2026)
Ranked October 2026. Prices, code summaries and rebate rules checked October 24, 2026; we re-rank monthly.
The best insulation for most attics is blown-in cellulose on an air-sealed attic floor, and blown-in fiberglass is a close second. Spray foam moves to the top only when you are sealing the attic at the roof deck, and then closed-cell spray foam is the first pick.
So the first question is where the insulation goes. DOE/PNNL's Building America Solution Center frames the choice this way: "Attic insulation can be installed on the attic floor if the attic will be a vented attic. Or insulation can be installed along the underside of the roof deck, which converts the attic to an unvented conditioned attic." HomeGuide's attic cost guide says to consider sealing the attic "if the attic contains HVAC equipment, ductwork, or stored items or when sealing the attic floor is too labor-intensive."
Sources: DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs (cites the 2018 IRC); HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026).
The ranking at a glance
Our example attic is a 1,200 sq ft ceiling under a 6/12 roof, so the roof deck above it measures about 1,342 sq ft (1,200 × 1.118, gable ends left out). Totals are our arithmetic on the published rates named in each row, rounded to $100, before removal, air sealing and minimum charges.
| Rank | Option | Where it goes | HomeGuide attic price per sq ft | Our total, 1,200 sq ft example | Best for |
|---|---|---|---|---|---|
| 1 | Blown-in cellulose | Vented attic floor | $0.90 to $2.40 (blown-in) | R-49: $1,300 to $2,300 | Most vented attics, low eaves |
| 2 | Blown-in fiberglass | Vented attic floor | $0.90 to $2.40 (blown-in) | R-49: $1,300 to $2,300 | Ceilings with ½-inch drywall on 24-inch framing, weight limits |
| 3 | Fiberglass batts | Vented attic floor | $0.80 to $2.60 | R-38: $1,300 to $4,000 | Do-it-yourself work on open, regular framing |
| 4 | Closed-cell spray foam | Underside of the roof deck | $1.50 to $5.00 (spray foam, either type) | R-49: $12,000 to $30,000 | Sealed attics with ducts or a furnace, cold zones, high-wind coasts |
| 5 | Open-cell spray foam | Underside of the roof deck | $1.50 to $5.00 (spray foam, either type) | R-38: $8,500 to $22,700 | Sealed attics in zones 1 to 4 on a tighter budget |
| 6 | Full-depth spray foam | Vented attic floor | $1.00 to $4.50 (spray foam) | Closed-cell R-38: $8,300 to $20,800 | Seldom pays off; a thin foam seal under fill does that work |
Blown-in totals use HomeGuide's blown-in table, which ties price to R-value ($1,100 to $1,900 per 1,000 sq ft at R-49) but does not name the material, so cellulose and fiberglass get one row. Batts use HomeGuide's R-38 batt rate, $1.10 to $3.30 per sq ft; it publishes no R-49 batt rate. Foam math takes Angi's installed rates of $0.60 to $1.60 per board foot for open-cell and $1.30 to $3.10 for closed-cell, at R-3.6 per inch for open-cell and R-6.8 to R-7.1 for closed-cell. Angi's attic guide puts the average 2026 attic job at $2,100, with most owners paying $1,700 to $2,500; its FAQ separately cites about $2,500, with a typical range of $1,500 to $3,500. Both are national figures, not local prices.
Sources: HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025); HomeGuide, "How Much Does Batt & Roll Insulation Cost? (2026)" (Nov 5, 2025); Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); Angi, "How Much Does Attic Insulation Cost? [2026 Data]" (updated Oct 12, 2026); Profoam product price sheet (R-value per inch column).
Attic floor or roof deck: settle this first
| Question | Vented attic floor | Sealed attic at the roof deck |
|---|---|---|
| Area insulated | 1,200 sq ft of ceiling | About 1,342 sq ft of deck and the gable walls |
| Vents | Stay open; baffles keep insulation off soffit vents | Soffit vents are blocked, per DOE/PNNL's retrofit steps |
| Ducts and air handler in the attic | Stay outside the insulated space | End up inside it |
| Materials that fit | Cellulose, fiberglass, batts, a thin foam seal | Spray foam, or foam with fill under it |
| Extra steps | Air seal the ceiling first | Roof repair, blocked soffits, insulated gables and a humidity plan (checklist below) |
| Price on our example | $1,300 to $2,300 at R-49 blown in | $8,500 to $30,000 in foam, by type and R-value |
DOE/PNNL lists the cases where a sealed attic "should be considered": the attic will be used as living space, it holds mechanical equipment or ductwork, the roof framing is hard to vent, or the ceiling is hard to air seal. It adds that low-slope roofs are good candidates, because there may not be room at the eaves for both insulation and a vent channel, and that sealed attics keep out wildfire embers and wind-driven rain. Outside those cases, the attic floor is the low-cost answer, which is why the floor options hold ranks 1 to 3.
Sources: DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs (cites the 2018 IRC); HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026).
1. Blown-in cellulose on the attic floor
Blown-in cellulose ranks first because blown-in fill is the lowest-priced route we found to the R-values ENERGY STAR recommends, and of the two common fills cellulose needs less depth and does more against air movement. DOE/PNNL's loose-fill table rates settled cellulose at R-3.2 to R-3.8 per inch and says it resists air movement better than loose fiberglass. The lower depth matters under low eaves: about 13 to 15 settled inches for R-49 by our math, against 18 to 22 for loose fiberglass. HomeGuide says blown-in "is ideal for most attics." Some utility programs favor it too: Ameren Missouri's 2026 Pay As You Save chart defines the attic measure as "Installation of blown-in cellulose insulation to a minimum of R-38."
Why it isn't perfect: DOE/PNNL puts settling at 10 to 20 percent for loose cellulose, so ask which R-value the bid quotes after settling. The same table gives cellulose a "No" over ½-inch drywall on framing 24 inches apart, because of its weight. HomeGuide says cellulose "lasts 20 to 30 years and starts degrading around the 15-year mark," against 80 to 100 years for fiberglass "in perfect conditions" and up to 30 years for foam "on the roof deck underside."
Sources: DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); Ameren Missouri, Pay As You Save rebate chart (valid January 1 to December 31, 2026).
2. Blown-in fiberglass on the attic floor
Blown-in fiberglass is the pick when the ceiling can't carry cellulose. DOE/PNNL gives loose fiberglass a "Yes" over ½-inch drywall at 24 inches on center and settling of only 2 to 4 percent. HomeGuide's blown-in rates price it the same as cellulose for a given R-value.
It ranks second on depth and airflow. Loose fiberglass rates R-2.2 to R-2.7 per settled inch, so R-60 for zones 4 to 8 takes about 22 to 27 inches.
Sources: DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); HomeGuide, "How Much Does Blown-in Insulation Cost? (2026)" (Nov 5, 2025).
3. Fiberglass batts on the attic floor
Batts are the do-it-yourself route. ENERGY STAR says "Laying fiberglass rolls is easiest for a DIY job," and it rates adding attic insulation in general "a moderately difficult do-it-yourself (DIY) project," taking 1 to 3 days for a homeowner against 1 to 2 for a contractor.
They rank below blown-in on price. HomeGuide's R-38 batt rate gives $1,300 to $4,000 on our example, so the high end is $1,700 above blown-in at R-49 for less R-value.
Sources: ENERGY STAR, Attic Insulation Project; HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); HomeGuide, "How Much Does Batt & Roll Insulation Cost? (2026)" (Nov 5, 2025).
4. Closed-cell spray foam under the roof deck
Closed-cell spray foam is the first pick for a sealed attic. DOE's Building America guide rates it "Preferred" for sloped roof rafters in all climates, because "the high R-value per inch means required assembly R-values are achievable even given the limits to allowable thicknesses," and it says deck-applied closed-cell foam strengthens the roof against wind storms. DOE adds that closed-cell foam of at least 2 inches "is not vapor permeable so in cold-climates a separate vapor retarder is not needed." HomeGuide agrees: "Closed-cell foam works best for roof decks in unvented attics."
What it costs: R-49 on our 1,342 sq ft deck takes 6.9 to 7.2 inches, or 9,262 to 9,670 board feet, or $12,000 to $30,000 at Angi's rates. At R-38 it is 5.4 to 5.6 inches and $9,300 to $23,200. It ranks fourth overall because that price only pays off when you need the sealed attic. The catch DOE names: a leak under closed-cell foam "may not be immediately apparent," so get the roof checked first.
Sources: U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); Profoam product price sheet (R-value per inch column).
5. Open-cell spray foam under the roof deck
Open-cell spray foam is the cheaper way to seal an attic. DOE rates it "Acceptable" at the roof deck in cold and hot-humid climates, and notes that when a roof leaks into open-cell foam, the material "will become wetted, but will dry given time and dry conditions." R-38 on our deck is 10.6 inches, 14,166 board feet and $8,500 to $22,700.
It ranks below closed-cell for two reasons. DOE says the allowed thickness "is dependant on individual manufacturer Evaluation Service Reports and varies between 5-1/2” and 10”," so R-38 and up may not be possible with every product; ask which report the bid relies on. And in climate zones 5 to 8, DOE/PNNL's summary of the 2018 IRC says foam under the deck must be a Class II vapor retarder or carry a Class II coating, which for open-cell means vapor-retarder paint. Our open-cell vs closed-cell comparison covers moisture and cost per R in more detail.
Sources: U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs (cites the 2018 IRC); Angi, "How Much Does Spray Foam Insulation Cost? [2026 Data]" (updated Sep 9, 2026); Profoam product price sheet (R-value per inch column).
6. Full-depth spray foam on the attic floor: last
Foam sprayed to full depth across a vented attic floor ranks last. DOE says full-depth foam on a vented attic ceiling is "not a common practice," and that open-cell foam there gives little more R per inch than cellulose or fiberglass at several times the price. On our example, closed-cell to R-38 on the floor is $8,300 to $20,800, several times the blown-in price at R-49.
Foam does have a role on the floor as a seal. DOE rates closed-cell "Preferred" there in the form of "a thin coating" for air sealing between the attic and the rooms below, and says blown fiberglass at least 1.5 inches deep over it counts as an ignition barrier under the IRC. HomeGuide says "Combining a thin spray foam layer with blown-in or batt insulation reduces the cost to air seal and achieve the desired R-value." If a bid proposes that combination, get the foam depth and the fill depth listed as separate lines.
HomeGuide says structural insulated panels are "primarily used in new construction," so we leave them unranked.
Sources: U.S. DOE Building America, "Which Spray Foam Is Right For You?" (CARB / Steven Winter Associates, 2009); HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); Angi, "How Much Does Attic Insulation Cost? [2026 Data]" (updated Oct 12, 2026).
What the cost guides charge by attic size
| Attic size | HomeGuide (Jan 13, 2026) | Angi (Oct 12, 2026) |
|---|---|---|
| 300 sq ft | Not listed | $300 to $900 |
| 500 sq ft | $500 to $2,000 | $500 to $1,500 |
| 800 sq ft | Not listed | $800 to $2,400 |
| 1,000 sq ft | $1,000 to $4,000 | $1,000 to $3,000 |
| 1,200 sq ft | $1,200 to $4,800 | Not listed |
| 1,500 sq ft | $1,500 to $6,000 | $1,500 to $4,500 |
| 2,000 sq ft | $2,000 to $8,000 | Not listed |
These rows aren't tied to one material or R-value, so treat them as a rough spread for a floor job. HomeGuide notes that some insulation companies have "a $1,500 to $2,000 minimum project requirement," above the low end for a 500 sq ft attic in its own table. Angi puts attic labor at $1.50 to $3 per sq ft and an inspection at $100 to $300. Timing can matter too: Angi's booking data puts October and November as the busiest months and April through June as the slowest.
Sources: HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); Angi, "How Much Does Attic Insulation Cost? [2026 Data]" (updated Oct 12, 2026).
What a sealed attic job adds
Moving insulation to the roof deck turns the attic into part of the house, and DOE/PNNL's retrofit steps add work a floor job never needs. Use them as a checklist when reading a roof deck bid:
- Roof first. Inspect shingles and framing for "deficiencies, rot, water damage, active leaks, insect damage" and "Consider roof replacement if roof is near end of service life."
- Dry, clean decking. The decking has to be dry and clean for the foam to stick; DOE/PNNL suggests checking the sheathing's moisture content first.
- Soffits and gables. Soffit vents get closed off, typically with "2x blocking or extended wall sheathing," and the gable end walls "must be insulated and air sealed," usually with the same foam.
- A plan for attic humidity. DOE/PNNL lists four: an exhaust fan at the attic peak paired with a motorized outdoor-air damper, balanced ventilation with heat or energy recovery, a dehumidifier, or ducted supply and return from the house system, which DOE/PNNL limits to foam that is not combustible or is covered. Building Science Corporation's Joe Lstiburek, quoted by DOE/PNNL, describes early sealed attics that stayed dry only because ducts leaked; once ductwork got tighter, "we ended up with very high humidity in the attics, and we discovered sweating on the ducts and mold on the mastic." The brief explains the cause as "hygric buoyancy": moisture-laden air is lighter than dry air, so it collects at the top of the house.
- Appliances. A furnace or water heater left in a sealed attic should be a "direct-vent sealed-combustion" unit, and DOE/PNNL says "combustion safety and controlled mechanical ventilation upgrades are required" after this retrofit.
- Quality control. DOE/PNNL calls spray foam a material "manufactured" on site and lists what to watch: the substrate's moisture, the thickness of each "lift," and the ratio of the two components. Cathedral ceilings with plaster or drywall at the roofline need that finish taken off first.
- Fire barrier. A thermal or ignition barrier goes over the foam where the product or code calls for one; DOE/PNNL notes "not all spray polyurethane foams require thermal or ignition barriers."
Two regional notes from the same guide. In zones 6 to 8, Building Science Corporation recommends keeping winter indoor humidity "below 35%" under a foamed roof. On coasts, DOE/PNNL says vented soffits "have been known to collapse" in high wind, leading to pressurization, window blowout and roof uplift; sealed attics avoid that and the "salt spray and corrosion" of truss plate connectors, and closed-cell foam adhesive along the sheathing joints can satisfy IBHS Fortified Home roof deck sealing.
Sources: DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs (cites the 2018 IRC); DOE/PNNL Building America Solution Center, Controlling Moisture in Unvented Attics, Code Compliance Brief (2015 IRC/IECC text and changes approved for the 2018 IRC).
How deep each option goes, by climate zone
| Zone | ENERGY STAR target, uninsulated attic | Target with 3 to 4 inches already there | Cellulose, settled | Loose fiberglass, settled | Open-cell foam | Closed-cell foam |
|---|---|---|---|---|---|---|
| 1 | R-30 | add R-25 | 7.9 to 9.4 in | 11.1 to 13.6 in | 8.3 in | 4.2 to 4.4 in |
| 2 and 3 | R-49 | add R-38 | 12.9 to 15.3 in | 18.1 to 22.3 in | 13.6 in | 6.9 to 7.2 in |
| 4 to 8 | R-60 | add R-49 | 15.8 to 18.8 in | 22.2 to 27.3 in | 16.7 in | 8.5 to 8.8 in |
Each inch figure is the uninsulated target divided by R per inch: DOE/PNNL's settled figures for the two fills, and our site-standard R-3.6 and R-6.8 to R-7.1 for foam. ENERGY STAR says its table is "based on the 2021 International Energy Conservation Code (IECC)," so it is a recommendation for existing houses, not your local code. Older editions asked for less: DOE/PNNL's summary of the 2012 and 2015 IECC/IRC lists ceiling R-30 in zone 1 and R-38 in zones 2 and 3. Our Phoenix cost page explains the 2024 IECC moving zones 2 and 3 back to R-38. Your city's adopted edition decides; the spray foam guide by climate zone lists the targets for every zone.
Sources: ENERGY STAR, Recommended Home Insulation R-Values (based on 2021 IECC Table R402.1.3); DOE/PNNL Building America Solution Center, Loose-Fill Insulation tool (table cites DOE, "Loose-Fill Insulations," May 1995); Profoam product price sheet (R-value per inch column); DOE/PNNL Building America Solution Center, Controlling Moisture in Unvented Attics, Code Compliance Brief (2015 IRC/IECC text and changes approved for the 2018 IRC).
Sealed attic code rules (IRC R806.5)
The IRC allows an unvented attic only when a list of conditions is met. These are the ones a homeowner will hear about most, with the edition each summary covers:
- Inside the envelope: "The unvented attic space is completely within the building thermal envelope." (2015 IRC text, as quoted by DOE/PNNL)
- No Class I vapor retarder on the attic floor side. DOE/PNNL's roof-deck guide says this applies in every climate zone, because it "will prevent drying to the inside in case of a roof leak." (2015 and 2018 IRC, per DOE/PNNL)
- Zones 5 to 8: "any air-impermeable insulation shall be a Class II vapor retarder" or carry a Class II coating. (2018 IRC, per DOE/PNNL)
- Foam with fill under it: the foam against the deck has to reach a minimum R-value for condensation control. DOE/PNNL's excerpt of 2015 IRC Table R806.5 gives R-5 for zones 1 to 3; the rest are on our climate zone guide.
- Fill only, no foam: The 2018 IRC added a vapor diffusion port option for zones 1 to 3 (R806.5 item 5.2), as DOE/PNNL describes. Ask your building department whether its edition has it before accepting a sealed attic with cellulose or fiberglass alone.
Sources: DOE/PNNL Building America Solution Center, Controlling Moisture in Unvented Attics, Code Compliance Brief (2015 IRC/IECC text and changes approved for the 2018 IRC); DOE/PNNL Building America Solution Center, Below Deck Spray Foam Insulation for Existing Roofs (cites the 2018 IRC).
Line items to expect on an attic bid
These are the extras the two cost guides price separately from the insulation:
| Line item | HomeGuide | Angi | When it applies |
|---|---|---|---|
| Air sealing the attic floor | $350 to $3,000 | $250 to $750 | Every floor job; ENERGY STAR: "EPA recommends air sealing the attic before adding attic insulation" |
| Removing old insulation | $1 to $2 per sq ft | $1 to $1.50 per sq ft | Old material with "fire, water, or pest damage," per HomeGuide |
| Soffit baffles | $2 to $3 each | No data | Vented attics, so fill can't block the vents |
| Roof vent installation | $200 to $700 | No data | Adding attic ventilation; HomeGuide also says "Vents exhausting into the attic must be vented outside before installing new insulation" |
| Pest inspection | $40 to $150 | No data | HomeGuide: "recommended before insulating an attic" |
| Attic cleaning | $100 to $500+ | No data | Moving stored items, mold or pest problems raise it, per HomeGuide |
| Attic mold removal | $1,500 to $15,000 | No data | Mold on rafters or joists, which ENERGY STAR says needs a professional first |
| Minor roof leak repair | $150 to $1,000 | No data | Wet insulation, "indicating a leaky roof," per ENERGY STAR |
| Attic inspection | No data | $100 to $300 | Angi says some contractors apply the fee to the project |
Electrical work is a separate trade. Angi says that if you are "moving wires, installing new wires, or installing new fixtures" in the space being insulated, a licensed electrician does that part. Laying new insulation over old does not require one.
Sources: HomeGuide, "How Much Does Attic Insulation Cost? (2026)" (Jan 13, 2026); Angi, "How Much Does Attic Insulation Cost? [2026 Data]" (updated Oct 12, 2026); ENERGY STAR, Attic Insulation Project.
Attic rebates and the materials they accept
Many attic rebates assume the insulation sits on the attic floor, or name the materials they pay for. The rules below are from our published city pages; the rest are in the 2026 insulation rebate tracker.
| Program | Attic rule | Spray foam or roof deck |
|---|---|---|
| Ameren Missouri PAYS | Blown-in cellulose to at least R-38 | Not in the attic measure |
| CenterPoint Houston Electric | 2026 ceiling materials list names only fiber and loose-fill products | Not on the list |
| PSO (Oklahoma) | $600; existing attic R-22 or less | Foam only as a Multiple Upgrade rebate |
| OG&E (Oklahoma) | Up to $500; insulation must sit between air-conditioned space and the attic | Not named; ask OG&E |
| TEP (Tucson) | Existing under R-19, final at least R-38 | Foam accepted; flat-roof deck foam counts when the attic becomes unvented and conditioned and the invoice says so; for pitched roofs, ask TEP |
| SRP (Phoenix area) | Up to 75% back, capped at $600, below R-19 raised to R-38, participating contractor | Not stated; ask SRP |
| Colorado Springs Utilities | 40% up to $1,250; R-49 with bypass air sealing | Not stated; ask CSU |
| Georgia Power | 50% up to $300 ($200 gas-heated); 2026 preconditions say existing insulation below R-19 (its FAQ says R-38 or less; confirm); whole attic to R-49 or state code as the structure allows | Spray foam (open or closed cell) needs a test-in and test-out assessment; ask Georgia Power about roof deck foam |
| TVA EnergyRight | $300 attic line; Quality Contractor Network members only | Not stated; ask TVA |
| Dominion Energy Virginia | Attic rebates only after a comprehensive home energy audit by a participating contractor, who submits the rebate | Not stated; ask Dominion |
City detail: Tucson, Phoenix, Colorado Springs, Atlanta, Tulsa, Nashville, Huntsville, Houston and the Missouri page. The 25C tax credit is gone for 2026 work: the IRS says it "will not be allowed for any property placed in service after December 31, 2025." Our grants vs rebates explainer covers grants, WAP and loans.
Sources: Ameren Missouri, Pay As You Save rebate chart (valid January 1 to December 31, 2026); CenterPoint Energy Houston Electric, 2026 Residential SOP Program Manual (August 2026); PSO Power Forward, Attic/Ceiling Insulation (R-22 or less existing); OG&E, Attic Insulation Rules and Guidelines, Oklahoma (PDF); TEP, 2026 Residential Insulation Program Application Form (PDF); SRP, Insulation Rebate; Colorado Springs Utilities, Residential rebate program rules; Georgia Power, HEIP Preconditions and Requirements 2026 (PDF); TVA EnergyRight, Residential Rebates; Dominion Energy Virginia, Home Energy Evaluation; IRS, FAQs on Public Law 119-21 changes to 25C and related credits.
Which one fits your attic
- Ducts or an air handler in the attic, humid climate: get a sealed roof deck priced in closed-cell foam next to a floor job. Our Houston, Tampa and Nashville cost pages price local roof decks against the attic floor.
- Plain vented attic, any climate: air seal, then blow cellulose or fiberglass to your zone's target. Spray foam vs fiberglass vs cellulose compares the fills in detail.
- Old drywall ceiling on 24-inch framing: blown fiberglass, not cellulose.
- Doing it yourself: batts, or rented-blower fill. For foam kits, see DIY spray foam kits vs hiring a pro.
- Cold zone (4 to 8), roof deck job: closed-cell, or open-cell with vapor-retarder paint. Colorado Springs and Omaha cost pages price it locally.
- Virginia: Dominion's rebates begin with the audit; our Charlottesville spray foam page has the local code edition and housing data.
Holding bids already? How to compare spray foam quotes puts them on the same footing, the quote checker checks a foam price against published rates, and the cost calculator prices your own roof deck. Insulating under the house too? See best insulation for crawl spaces.
Attic insulation FAQ
What is the best insulation for an attic?
For a vented attic, blown-in cellulose over an air-sealed attic floor ranks first on our list, with blown-in fiberglass second. For an attic you are sealing at the roof deck, closed-cell spray foam ranks first. On our 1,200 sq ft example attic, R-49 blown in prices at $1,300 to $2,300, against $12,000 to $30,000 for closed-cell foam on the roof deck above it.
Is spray foam worth it in an attic?
Usually only when the attic is being sealed. DOE/PNNL suggests an unvented attic when it will hold living space, when it contains mechanical equipment or ductwork, when the roof is hard to vent, or when the ceiling is hard to air seal. On a plain vented attic floor, DOE calls full-depth closed-cell foam "not a common practice."
How many inches of attic insulation do I need?
It depends on your climate zone and the material. ENERGY STAR recommends R-49 for an uninsulated attic in zones 2 and 3 and R-60 in zones 4 to 8. By our math on DOE/PNNL figures, R-49 takes about 13 to 15 settled inches of cellulose or 18 to 22 inches of loose fiberglass.
Should I seal the attic if my ducts are up there?
It is the main reason to consider it. DOE/PNNL lists ductwork and mechanical equipment in the attic among the cases where an unvented attic "should be considered." A sealed attic also needs a humidity plan, such as a dehumidifier or conditioned supply air, and any combustion appliance there should be a sealed-combustion unit.
Will my utility rebate pay for spray foam in the attic?
Not always. Ameren Missouri's 2026 PAYS chart defines the attic measure as blown-in cellulose, PSO pays for foam only as a Multiple Upgrade rebate, and several programs on our list are silent on roof deck foam. Get the utility's answer before you sign.