By The Roofing Brief Team. Last reviewed: October 2026.
R-49 insulation is a ceiling insulation level, not a product: it takes 17 inches of Owens Corning AttiCat blown fiberglass, 13.3 inches settled of Greenfiber SANCTUARY cellulose, a single 14-inch Owens Corning PINK Next Gen R-49 batt, or about 7 inches of closed-cell spray foam. Under the 2021 IECC it is the ceiling minimum in climate zones 2 and 3, while zones 4 through 8 require R-60 unless R-49 runs at full height over the wall top plate (Section R402.2.1). For an existing attic in zones 4 through 8 that already has 3 to 4 inches, ENERGY STAR sets R-49 as the top-up target.
Which R-49 route fits your roof
The decision turns on three measurements: the clear height at the eaves, the rafter or joist depth, and whether your building department enforces the 2018 or the 2021 IECC.
| If your situation is | Route to R-49 | Threshold or rule | Source |
|---|---|---|---|
| Open attic floor with room above the joists | Blown fiberglass to 17 in (AttiCat) or 18.5 in (InsulSafe SP) | 25 to 25.2 bags per 1,000 sq ft; $1,100 to $1,900 installed per 1,000 sq ft | Owens Corning, CertainTeed coverage charts; HomeGuide (Nov 2025) |
| Open attic floor, but less than 17 in of height near the eaves | Blown cellulose (13.3 in settled) or a 14 in R-49 batt | Code counts the settled R-value for blown-in (IECC R402.1.4) | Greenfiber SANCTUARY chart; Owens Corning submittal |
| Clean joist bays, no blower rental | One 14 in R-49 batt, or R-30 (9.5 in) plus R-19 (6.5 in) run crosswise | Stacked layers total about 16 in | Owens Corning PINK Next Gen submittal (Sept 2025) |
| Cathedral ceiling, rafters 2×8 or deeper, no attic | Closed-cell spray foam in the rafter bays | Heatlok HFO: R-45 at 6.0 in, R-52 at 7.0 in; 6.5 in maximum per pass | ICC-ES ESR-4073 Table 1 |
| Low-slope roof being reroofed | Two layers of polyiso above the deck | 4.0 in plus 4.3 in boards reach R-49.1 at 8.3 in | Sika Sarnatherm ISO data sheet (Aug 2024) |
| Ceiling without an attic where the full depth will not fit | R-30 allowed under the 2021 IECC | Limited to 500 sq ft or 20 percent of insulated ceiling, whichever is less | 2021 IECC R402.2.2 |
| New build in zones 4 to 8 under the 2021 IECC | R-60, or R-49 over 100 percent of the ceiling | R-49 counts only where its full uncompressed height extends over the wall top plate at the eaves | 2021 IECC R402.2.1 |
| Existing attic with 3 to 4 in already, zones 4A through 8 | Top up to R-49 | Uninsulated attics in those zones target R-60 instead | ENERGY STAR retrofit table |
What R-49 insulation means
R-49 means a completed insulation layer resists conductive heat flow to a rating of 49, on a scale where a higher number slows heat loss more. R-value is additive: two R-25 layers stacked read as roughly R-50. R-49 is a whole-assembly target for an attic floor or ceiling, reached by any material once it is installed to the right depth.
No single product is “R-49.” You hit the number with fiberglass batts, blown fiberglass, blown cellulose, mineral wool, or spray foam, each at a different depth. That is why the same R-49 can be about 7 inches of closed-cell foam or 17 to 18.5 inches of blown fiberglass. For the exact depth math by material, see our R-49 insulation thickness by material breakdown.
Where R-49 insulation is required
R-49 is the 2021 IECC ceiling minimum only in climate zones 2 and 3. In zones 4 through 8, the 2021 code raised the ceiling minimum to R-60, so R-49 no longer meets new-construction code there unless a specific truss exception applies. Many states still enforce the older 2018 IECC, under which R-49 remains the ceiling minimum across zones 4 through 8. Your jurisdiction decides which applies.
New construction under the 2021 IECC
Under 2021 IECC Table R402.1.3 (insulation minimum R-values by component), ceiling insulation minimums step up by zone. R-49 satisfies zones 2 and 3. Colder zones now require R-60. If your state adopted the 2021 code, R-49 in a zone 5 or 6 attic would fail inspection unless the raised-heel exception is used. Florida homeowners can check their minimums in our guide to the best attic insulation for Florida.
| Climate zone | 2021 IECC ceiling minimum | Where R-49 fits |
|---|---|---|
| Zone 1 | R-30 | Exceeds the minimum |
| Zones 2 and 3 | R-49 | Meets the minimum |
| Zones 4 through 8 | R-60 | Below minimum unless the raised-heel truss exception applies |
Adding insulation to an existing attic
For retrofits, ENERGY STAR’s recommended R-values table ties the target to what is already there. An uninsulated attic in zones 2 and 3 should reach R-49, while zones 4 through 8 should reach R-60. An attic that already holds 3 to 4 inches of insulation in a cold zone should be topped up to about R-49. This is where R-49 stays a common real-world target even in cold climates.
| Climate zone | Uninsulated attic target | Attic with 3 to 4 inches existing |
|---|---|---|
| Zone 1 | R-30 | R-25 |
| Zones 2 and 3 | R-49 | R-38 |
| Zones 4 through 8 | R-60 | R-49 |
The raised-heel truss exception
2021 IECC Section R402.2.1 (ceilings with attics) works in two steps. Where the table requires R-49 (zones 2 and 3), R-38 over 100 percent of the ceiling satisfies it; where the table requires R-60 (zones 4 through 8), R-49 over 100 percent of the ceiling satisfies it. Both reductions apply only where the full height of the uncompressed insulation extends over the wall top plate at the eaves, and neither applies to the Total UA alternative in R402.1.5. A standard truss pinches the eave to a few inches, so this credit usually needs a raised-heel (energy-heel) truss. Ask the builder for the heel height on the truss drawings: it has to clear the full R-49 depth of the chosen material, for example 17 in for AttiCat.
How thick R-49 insulation is by material
R-49 lands at very different depths depending on the material, because each has its own R-value per inch. A single R-49 fiberglass batt is 14 inches thick and blown cellulose achieves R-49 at about 14.3 inches installed (13.3 inches settled), R-49 blown fiberglass insulation runs deeper at 17 to 18.5 inches, and closed-cell spray foam gets there in about 7 inches. The table below is a quick reference; the full per-material math is in the R-49 thickness guide.
| Material (named product) | Depth for R-49 | R-value per inch | Bags per 1,000 sq ft | Source |
|---|---|---|---|---|
| Fiberglass batt (Owens Corning PINK Next Gen) | 14 in (single R-49 batt); 16 in (R-30 plus R-19 stacked) | 3.5 | Batts, not bags | OC submittal sheet, Sept 2025 |
| Blown fiberglass (Owens Corning AttiCat) | 17 in | 2.9 | 25 | OC AttiCat data sheet, May 2026 |
| Blown fiberglass (CertainTeed InsulSafe SP) | 18.5 in | 2.65 | 25.2 | CertainTeed InsulSafe SP chart |
| Blown cellulose (Greenfiber SANCTUARY) | 14.3 in installed, 13.3 in settled | 3.7 | 70.8 (25 lb bags) | Greenfiber SANCTUARY fact sheet, Rev K |
| Closed-cell spray foam (Huntsman Heatlok HFO) | Between 6.0 in (R-45) and 7.0 in (R-52) | About 7 to 7.4 | Sprayed, not bagged | ICC-ES ESR-4073, Table 1 |
R-value per inch for the blown and batt rows is R-49 divided by the listed depth. Coverage charts set both a minimum thickness and a minimum bag count; meeting only one does not deliver the rated R-value, per the Greenfiber and Owens Corning chart notes.
Depth matters for more than the number. In a shallow attic or against roof rafters, closed-cell foam reaches R-49 in half the space of blown fiberglass. In an open attic floor with room to spare, blown material is far cheaper per R: HomeGuide puts blown-in R-49 at $1,100 to $1,900 per 1,000 sq ft installed. See the full insulation R-value chart for every material and zone.
How to achieve R-49 in a roof without an attic floor
Without an open attic floor, R-49 has to fit inside the rafters or on top of the roof deck, where 14 to 18.5 inches of loose fill will not go. The practical options are closed-cell spray foam in the rafter bays (about 7 inches; a 2×8 rafter is 7.25 inches deep) or rigid foam board above the deck. Polyiso board reaches R-49 at about 8.3 inches in two layers; XPS needs about 9.8 inches.
Rigid board ratings come from manufacturer data sheets. The Sika Sarnatherm ISO polyiso data sheet (August 2024) lists a long-term thermal resistance (LTTR) of R-23.6 at 4.0 inches and R-25.5 at 4.3 inches, so those two boards stacked reach R-49.1 at 8.3 inches. Its thickest single board is 4.5 inches (R-26.8), so R-49 above a deck always takes at least two layers. Owens Corning rates FOAMULAR NGX 250 XPS (October 2025 data sheet) at R-5.0 per inch at a 75°F mean temperature, which puts R-49 at about 9.8 inches of board.
| Material | Rated R-value | Depth for R-49 |
|---|---|---|
| Closed-cell spray foam (Heatlok HFO, ESR-4073) | R-45 at 6.0 in; R-52 at 7.0 in | About 7 in, sprayed in two passes of 6.5 in or less |
| Polyiso rigid board (Sika Sarnatherm ISO) | R-23.6 at 4.0 in; R-25.5 at 4.3 in (LTTR) | 8.3 in in two layers (R-49.1) |
| XPS rigid board (Owens Corning FOAMULAR NGX 250) | R-5.0 per inch at 75°F | About 9.8 in |
| Blown fiberglass, for comparison | R-2.65 to 2.9 per inch | 17 to 18.5 in |
Some roofs cannot hold the full depth, and codes account for that. In the 2018 IRC (Section N1102.2.2, the same provision as IECC R402.2.2), a ceiling without an attic space may drop to R-30 where the roof design lacks room for the required insulation, if the insulation runs uncompressed over the wall top plate. The reduction is capped at 500 square feet or 20 percent of the total insulated ceiling area, whichever is less, per the ICC’s summary of that section. Whether it applies depends on the code edition your jurisdiction enforces, so confirm with your building department before you design around it.
On a low-slope roof, the two polyiso boards above raise the finished roof by at least 8.3 inches, so curb heights, scuppers and edge metal have to be checked against that new height before the tear-off. Our guide to commercial flat roof insulation compares board types, R-values and cost.
R-49 vs R-60: which to install
R-60 adds about 22 percent more thermal resistance than R-49 and is the 2021 IECC minimum for zones 4 through 8. The jump from R-49 to R-60 means about 3 to 3.5 more inches of blown material on the AttiCat, InsulSafe SP and SANCTUARY charts and delivers diminishing returns: each added R-value cuts a smaller slice of remaining ceiling heat loss. In a cold zone new build, R-60 is usually the code answer; in a retrofit, R-49 is often the practical target.
| Factor | R-49 | R-60 |
|---|---|---|
| Blown depth | 14.3 in (cellulose) to 18.5 in (fiberglass) | 17.3 in (cellulose) to 22 in (fiberglass) |
| 2021 IECC role | Zones 2 and 3 minimum | Zones 4 through 8 minimum |
| Relative ceiling heat loss | Baseline | About 18 percent less through the insulation layer (1/60 vs 1/49) |
| Best fit | Warm-zone code, cold-zone retrofit | Cold-zone new construction |
If your attic has the depth and you are already paying for a blower, topping to R-60 adds about $300 to $500 per 1,000 sq ft installed: HomeGuide’s blown-in cost table (Nov 2025) lists R-49 at $1,100 to $1,900 and R-60 at $1,400 to $2,400 per 1,000 sq ft. Our R-60 insulation thickness guide shows the depth by material.
What R-49 insulation costs
Reaching R-49 in a 1,000 square foot attic runs about $1,100 to $1,900 installed with blown material, per HomeGuide’s blown-in cost guide (November 2025), of which $720 to $1,000 is material (24 to 26 bags). Stacked batts cost more because they are two installs: HomeGuide’s batt guide lists R-30 at $1.00 to $3.00 and R-19 at $0.90 to $2.30 per sq ft installed. Two things move the price most: removing old insulation first, and contractor minimums, which HomeGuide puts at $1,500 to $2,000 per project for some firms.
| Material | Cost to R-49 (per sq ft) | 1,000 sq ft attic | Source |
|---|---|---|---|
| Blown fiberglass or cellulose, installed | $1.10 to $1.90 | $1,100 to $1,900 | HomeGuide blown-in guide, Nov 2025 |
| Blown-in, material only (24 to 26 bags) | $0.72 to $1.00 | $720 to $1,000 | HomeGuide blown-in guide, Nov 2025 |
| Batts, R-30 plus R-19 stacked, installed | $1.90 to $5.30 (sum of the two layers) | $1,900 to $5,300 | HomeGuide batt and roll guide, Nov 2025 |
| Closed-cell spray foam, installed | HomeGuide lists $3.00 to $5.00 for closed-cell without stating a thickness | Quote by the board foot: R-49 at 7 in is 7 board feet per sq ft | HomeGuide spray foam guide, Dec 2025 |
The federal 25C insulation credit (30 percent of materials, capped at $1,200 a year) applied only to improvements made through December 31, 2025, per the IRS Energy Efficient Home Improvement Credit page; Public Law 119-21 ended it for later work. For 2026 projects, state and utility rebates are the remaining path where your program offers them. Check current rules in our attic insulation tax credit and rebates guide before you count on a discount.
Batts or blown-in for reaching R-49
Blown-in insulation reaches R-49 in one pass and fills irregular cavities and gaps that batts leave open, which is why most attic top-ups use it. Batts can match the R-value and suit a clean, open joist bay, but hitting R-49 usually means stacking two layers with the second run perpendicular, and any gap around wiring or framing cuts real-world performance. For a full attic floor, blown material usually wins on speed and coverage. For the material math, see our breakdown of the cost of R-49 in batts vs blown-in.
| Factor | Fiberglass batts | Blown-in |
|---|---|---|
| Reaching R-49 | Two stacked layers | Single pass |
| Coverage of gaps | Leaves gaps at obstructions | Fills irregular cavities |
| DIY difficulty | Doable by hand | Needs a blower rental |
| Settling | None | SANCTUARY cellulose settles from 14.3 in to 13.3 in at R-49, about 93 percent (Greenfiber chart) |
Whichever you pick, three code details decide whether the R-49 performs. Air seal the attic floor first, because blown and batt insulation are air-permeable. In a vented attic, 2021 IECC R402.2.3 requires an eave baffle beside each soffit vent that extends over the top of the insulation, so at 17 in of AttiCat the baffle has to rise at least that high. Under R402.2.4, the attic hatch must be insulated to the same R-value as the ceiling around it. For a full material rundown, see our guides to blown-in insulation and the best insulation for your attic.
Frequently asked questions
Is R-49 insulation enough for an attic?
R-49 is enough in climate zones 2 and 3, where it meets the 2021 IECC ceiling minimum. In zones 4 through 8, the 2021 code calls for R-60, so R-49 is below new-construction code unless a raised-heel truss exception applies or your state still enforces the 2018 IECC. For a cold-zone retrofit, R-49 is a common and acceptable ENERGY STAR target.
How many inches is R-49 insulation?
R-49 is 14 inches for a single R-49 fiberglass batt (16 inches for stacked R-30 plus R-19), 17 to 18.5 inches of blown fiberglass, about 14.3 inches of blown cellulose settling to 13.3, or roughly 7 inches of closed-cell spray foam, per current manufacturer charts. The depth changes because each material has a different R-value per inch. Blown fiberglass is the deepest common option; spray foam is the shallowest.
Is R-49 the same as R-60?
No. R-60 provides about 22 percent more thermal resistance than R-49 and needs about 3 to 3.5 more inches of blown material. Under the 2021 IECC, R-49 is the ceiling minimum for zones 2 and 3, while R-60 is the minimum for zones 4 through 8. The gain from R-49 to R-60 is real but shows diminishing returns.
Does R-49 insulation meet code?
It depends on your climate zone and adopted code. Under the 2021 IECC, R-49 meets ceiling code in zones 2 and 3 but not zones 4 through 8, which require R-60. Under the older 2018 IECC, still enforced in many states, R-49 meets code across zones 4 through 8. Confirm which code your local building department uses.
How much does R-49 insulation cost?
Reaching R-49 in a 1,000 square foot attic usually costs about $1,100 to $1,900 installed with blown material, per HomeGuide (November 2025). Stacked R-30 plus R-19 batts run about $1,900 to $5,300 installed on HomeGuide’s per-layer prices, and closed-cell spray foam is quoted by the board foot, 7 board feet per square foot at R-49. Removing old insulation first adds to any of these.
Can you get R-49 with fiberglass batts?
Yes. R-49 with fiberglass batts usually means two stacked layers, such as an R-30 batt (9.5 inches) topped with an R-19 batt (6.5 inches) run perpendicular, about 16 inches total; Owens Corning also lists a single 14-inch R-49 batt. Batts work best in clean, open joist bays. Any gaps around wiring, framing, or fixtures reduce the real R-value, so many installers prefer blown-in for full attic coverage.
How many bags of blown-in insulation for R-49?
For 1,000 square feet of attic, R-49 takes 25 bags of Owens Corning AttiCat at 17 inches, 25.2 bags of CertainTeed InsulSafe SP at 18.5 inches, or 70.8 bags (25 lb) of Greenfiber SANCTUARY cellulose at 14.3 inches installed, per each maker’s coverage chart. Install both the bag count and the depth: the charts say meeting only one does not deliver the rated R-value.