By The Roofing Brief Team. Last reviewed: October 2026. Thicknesses come from manufacturer coverage charts and data sheets (Owens Corning, Johns Manville, CertainTeed, Greenfiber, ROCKWOOL, Huntsman), each linked where it is used.
R-49 insulation thickness is about 14 inches for a single fiberglass batt, 13.7 inches of settled blown cellulose, 17 to 18.25 inches of blown fiberglass, and about 6.6 inches of closed-cell spray foam. The Owens Corning PINK Next Gen R-49 batt is 14 inches thick. Greenfiber’s INS541LD cellulose attic card lists R-49 at 15.20 inches installed and 13.68 inches settled. Blown fiberglass charts from Owens Corning, Johns Manville and CertainTeed put R-49 at 17 to 18.25 inches. Rigid board above a roof deck takes about 8.4 inches of polyiso or 9.8 inches of XPS. Under the 2021 IECC, R-49 is the attic minimum for climate zones 2 and 3; zones 4 through 8 moved up to R-60, per the ENERGY STAR recommended R-values table, which is based on 2021 IECC Table R402.1.3.
The depth math is 49 divided by the product’s R-value per inch, then checked against the bag or batt label. Huntsman lists its Icynene Classic open-cell foam at R-3.7 per inch, so 49 / 3.7 = 13.2 inches. For loose-fill, the label does the math for you: the FTC R-value Rule, 16 CFR 460.12, requires every loose-fill bag to print the minimum settled thickness, initial installed thickness, bags per 1,000 sq ft and minimum weight per sq ft at R-49.
How many inches is R-49 insulation by material?
R-49 takes about 6.6 to 18.25 inches of material, set by the product’s R-value per inch. Closed-cell spray foam at R-7.4 per inch (Huntsman Heatlok HFO Pro) needs the least depth. Blown fiberglass, at roughly R-2.7 to R-2.9 per inch on the charts below, needs the most.
| Material | Example product and maker figure | Thickness for R-49 | Source |
|---|---|---|---|
| Fiberglass batt (single) | Owens Corning PINK Next Gen R-49, 14 in (about R-3.5 per in) | 14 in | Owens Corning |
| Fiberglass batt (stacked) | R-38 batt at 12 in plus R-13 at 3.5 in = R-51 | 15.5 in | Owens Corning PINK Next Gen data sheet |
| Blown fiberglass (loose-fill) | AttiCat 17 in; Climate Pro B-7700 17 in; InsulSafe SP 18.25 in | 17 to 18.25 in | Maker coverage charts (table below) |
| Blown cellulose | Greenfiber INS541LD: 15.20 in installed, 13.68 in settled | 13.68 in settled | Greenfiber attic card |
| Mineral wool batt (stacked) | ROCKWOOL Comfortbatt R-38 at 9.5 in plus R-13 at 3.5 in = R-51 | 13 in | ROCKWOOL data sheet (07-2026) |
| Open-cell spray foam | Icynene Classic R-3.7 per in; Classic Plus R-4.0 per in | 12.25 to 13.2 in | Huntsman |
| Closed-cell spray foam | Heatlok HFO Pro R-7.4 per in, 6.5 in maximum lift per pass | about 6.6 in (two passes) | Huntsman |
| Polyiso board | JM ENRGY 3: two 4.2 in boards at R-24.9 each = R-49.8 | 8.4 in | Johns Manville data sheet (linked below) |
| XPS board | FOAMULAR NGX 250 R-5.0 per in | about 9.8 in | Owens Corning data sheet (linked below) |
A single maker’s data sheet gives one exact figure, so read the bag or batt label for the product you actually buy; under 16 CFR 460.12 every batt label must show R-value and thickness. The insulation R-value chart lists per-inch values across every common material if you need to compare options side by side.
Which route to R-49 fits your attic?
| If your attic or roof has… | Route to R-49 | Depth needed | Rule or source |
|---|---|---|---|
| Open attic floor, no insulation, joists 2×6 to 2×10 | Blown cellulose or blown fiberglass to the label depth | 13.68 in settled cellulose; 17 to 18.25 in fiberglass | 16 CFR 460.12 label; depth markers 1 per 300 sq ft (2021 IRC N1101.10.1.1) |
| Open joist bays and no blowing machine | One unfaced R-49 batt (16 or 24 in wide) laid between or across joists | 14 in | Owens Corning PINK Next Gen data sheet |
| 3 to 4 in of old insulation already down (zones 4 to 8) | Add R-49 on top, per ENERGY STAR retrofit table | add 14 in batt or 17 in blown fiberglass | ENERGY STAR, based on 2021 IECC |
| Raised-heel trusses with full R-38 height over the top plates | R-38 over 100% of the ceiling is deemed to meet an R-49 requirement | 12 in batt or 13.5 in AttiCat | 2021 IECC R402.2.1 |
| Cathedral ceiling or 2×10 rafter bay (9.25 in) | Closed-cell spray foam, or R-30 where the code exception applies | about 6.6 in at R-7.4 per in | 2021 IECC R402.2.2 allows R-30 on up to 500 sq ft or 20% of ceiling area, whichever is less |
| Low-slope roof, insulation above the deck | Two layers of polyiso, joints staggered | 8.4 in | JM ENRGY 3 LTTR table |
| House in zones 4 to 8 permitted under the 2021 IECC | R-49 is below code; target R-60 | about 20.5 in AttiCat or 16.53 in settled cellulose | R-60 insulation thickness |
How thick is R-49 fiberglass batt insulation?
R-49 fiberglass batt insulation is 14 inches thick as a single batt: Owens Corning lists its PINK Next Gen R-49 batt at 14 inches, and Home Depot lists it kraft-faced in 16 in by 48 in (BF92) and 24 in by 48 in (BF93) sizes. Where a single R-49 batt is not stocked, installers stack layers: the same data sheet lists R-38 at 12 inches and R-13 at 3.5 inches, so the pair gives R-51 at 15.5 inches when the top layer runs perpendicular to the joists to cover the framing.
Because standard attic joists are 2×10 (9.25 inches deep) or 2×12 (11.25 inches deep), a 14-inch R-49 batt sits 2.75 to 4.75 inches above the joist tops. That is normal and expected for R-49; the insulation should mound over the framing, not be pushed down into it. Owens Corning sells a separate high-density R-38C batt at 10.25 inches for shallow cavities, which shows why a standard batt squeezed to the same depth does not keep its label rating.
How many inches of blown insulation for R-49?
Blown insulation for R-49 runs 13.68 inches of settled cellulose or 17 to 18.25 inches of blown fiberglass, and the chart for the exact product decides the number. Several contractor guides quote 14 to 16 inches for blown fiberglass; the three maker charts below say 17 inches or more. Always measure against the label’s minimum settled thickness, not the freshly blown height.
| Product (chart date) | Type | Installed depth for R-49 | Settled depth for R-49 | Bags per 1,000 sq ft | Source |
|---|---|---|---|---|---|
| Owens Corning AttiCat (2026) | Blown fiberglass | 17 in | 17 in | 25 | AttiCat data sheet |
| Johns Manville Climate Pro B-7700 (9/25) | Blown fiberglass | 17.00 in | 17.00 in | 22.4 | JM data sheet |
| CertainTeed InsulSafe SP (10/25) | Blown fiberglass | 18.25 in | 18.25 in | 23.5 | CertainTeed technical notes |
| Greenfiber INS541LD (03/20) | Blown cellulose | 15.20 in | 13.68 in | see chart | Greenfiber attic card (linked above) |
Cellulose settles and fiberglass mostly does not: Greenfiber’s chart drops from 15.20 to 13.68 inches at R-49, about 10 percent, while all three fiberglass charts list the same installed and settled depth. Installers blow to the initial installed thickness and mark that number on depth markers stapled to the joists, at least one per 300 sq ft, as the 2021 IRC (Section N1101.10.1.1) requires. For spacing and marking, see our guide to attic rulers. CertainTeed’s sheet notes up to 18% R-value loss at R-49 under Bemidji, MN winter design conditions, and Owens Corning’s AttiCat chart adds 2.0 inches at R-49 to meet Minnesota’s winter-design-temperature rule.
For a full breakdown of loose-fill options, coverage, and DIY versus pro pricing, see the guide to blown-in insulation.
How thick is R-49 spray foam?
R-49 spray foam is about 6.6 inches for closed-cell and 12.25 to 13.2 inches for open-cell. Huntsman rates Heatlok HFO Pro closed-cell foam at R-7.4 per inch with a 6.5-inch maximum lift per pass, so R-49 (6.6 inches) takes two passes. That makes closed-cell the usual choice when depth is tight, such as insulating a rafter cavity for a conditioned attic.
Open-cell foam is lighter and cheaper per board foot but delivers only R-3.7 (Icynene Classic) to R-4.0 (Classic Plus) per inch on Huntsman’s figures, so it needs 12.25 to 13.2 inches to reach R-49. A standard 2×10 rafter (9.25 inches deep) cannot hold that without furring the rafters out by 3 to 4 inches or accepting a lower R-value. See spray foam attic insulation for open versus closed cell cost and R-value details.
How thick is R-49 rigid foam board insulation?
R-49 in rigid foam board takes about 8.3 to 8.6 inches of polyiso or about 10 inches of XPS. Rigid board usually goes on top of the roof deck or under a low-slope membrane, not on an attic floor, and R-49 takes two or more layers. Two 4.2-inch polyiso boards rated R-24.9 each reach R-49.8 at 8.4 inches. Our guide to attic foam board insulation covers the attic spots where board does fit.
| Board type | Rated R-value per inch | Thickness for R-49 |
|---|---|---|
| Polyiso (polyisocyanurate) | R-5.7 at 1 in, rising to about R-5.9 at 4 in and up (LTTR) | about 8.3 to 8.6 in |
| XPS (extruded polystyrene) | R-5.0 | about 9.8 in |
| EPS (expanded polystyrene) | Lower than XPS, varies by ASTM C578 type | more than XPS; check the product sheet |
The polyiso figures come from the Johns Manville ENRGY 3 data sheet, which lists long-term thermal resistance (LTTR) by board thickness: R-23.6 at 4.0 inches and R-24.9 at 4.2 inches, tested at a 75°F mean temperature. The XPS figure is R-5.0 per inch at 75°F from the Owens Corning FOAMULAR NGX 250 data sheet. Stagger the joints between layers so no seam runs straight through the full depth.
Board thickness is set by the product, so R-49 rarely lands on a single sheet: two 4.2-inch ENRGY 3 boards give R-49.8, while one 4.0-inch board plus one 4.2-inch board gives only R-48.5. Add up the rated R-value of each layer from the maker’s LTTR table rather than multiplying a per-inch average. On a low-slope roof the boards sit under the membrane; see our guide to commercial flat roof insulation types and R-values for how those assemblies are built.
Which climate zones require R-49?
R-49 is the attic insulation minimum in the 2021 International Energy Conservation Code (IECC) for climate zones 2 and 3, the southern and lower mid-latitude states. Zones 4 through 8 call for R-60 and zone 1 for R-30, per Table R402.1.3 as reproduced by ENERGY STAR. The older 2018 IECC (Table R402.1.2) set R-49 for zones 4 through 8 and R-38 for zones 2 and 3, and many jurisdictions still enforce the 2018 edition or an amended code, so confirm the adopted edition with your building department. Our guide on where R-49 insulation is required also covers what it costs and how to reach it in a roof without an attic floor.
For existing homes, ENERGY STAR’s retrofit table recommends adding R-49 on top of 3 to 4 inches of existing insulation in zones 4 through 8, and R-38 on top in zones 2 and 3. R-49 is a common upgrade target for older homes that were originally built to R-19 or R-30.
R-49 versus R-38 and R-60 thickness
R-49 sits between R-38 and R-60 on both the code ladder and the depth chart. On Greenfiber’s INS541LD chart, settled cellulose runs 10.77 inches at R-38, 13.68 at R-49 and 16.53 at R-60; Owens Corning’s AttiCat runs 13.5, 17 and 20.5 inches. Match your target to your climate zone and code edition first, then read the thickness off the material row.
| R-value | IECC ceiling zones | Blown cellulose, settled (Greenfiber INS541LD) | Blown fiberglass (AttiCat) | Fiberglass batt (Owens Corning) |
|---|---|---|---|---|
| R-38 | Zones 2 to 3 (2018 IECC) | 10.77 in | 13.5 in | 12 in |
| R-49 | Zones 2 to 3 (2021 IECC); zones 4 to 8 (2018 IECC) | 13.68 in | 17 in | 14 in |
| R-60 | Zones 4 to 8 (2021 IECC) | 16.53 in | 20.5 in | 17.5 in stacked (R-49 plus R-13 = R-62) |
If your code calls for a different level, compare the full material tables on the R-38 insulation thickness and R-60 insulation thickness pages.
How to hit R-49 when attic depth is limited
When joist depth cannot hold 14 or more inches of batt or loose-fill, there are four routes to R-49: a higher-R material, raised framing, layered materials, or the R-38 deemed-to-comply rule at the eaves (2021 IECC R402.2.1). Which one fits depends on whether the insulation sits on the attic floor or against the roof deck. For the layered route, our guide to attic insulation rolls covers roll sizes and how many to buy.
- Use a higher-R material. Closed-cell spray foam at R-7.4 per inch reaches R-49 in about 6.6 inches, fitting where batts cannot. This is the common fix for shallow rafter cavities in a conditioned attic.
- Add furring or a raised platform. A 14-inch R-49 batt needs 4.75 inches more height than a 2×10 joist (9.25 inches) provides, so a storage platform over 2x10s must sit on risers of at least 4.75 inches to avoid crushing the batt.
- Layer batt over blown-in. Greenfiber INS541LD cellulose settles at 8.62 inches for R-30; an unfaced R-19 batt (6.5 inches on the Owens Corning sheet) laid across the top, perpendicular to the joists, brings the total to R-49 at about 15.1 inches.
- Keep baffles at the eaves. Whatever the depth, install ventilation baffles so insulation does not block soffit airflow. See attic insulation baffles for placement.
Never compress insulation to make it fit. The Insulation Institute (NAIMA) compressed R-value chart rates a 14-inch R-49 batt squeezed into a 2×12 cavity (11.25 inches) at about R-42, and a 12-inch R-38 in a 2×10 at R-32. A batt pushed below its labeled thickness no longer delivers its labeled R-value, which is why Owens Corning makes the high-density R-38C at 10.25 inches instead of asking installers to squeeze a 12-inch R-38. If space is genuinely tight, a higher-R material or the 2021 IECC R402.2.2 exception (R-30 on up to 500 sq ft or 20% of the ceiling) is the honest way to stay within code.
Frequently asked questions
How many inches is R-49 insulation?
R-49 insulation is about 6.6 to 18.25 inches thick, depending on material. A single Owens Corning R-49 fiberglass batt is 14 inches, settled blown cellulose is 13.68 inches on Greenfiber’s INS541LD chart, blown fiberglass is 17 to 18.25 inches on the AttiCat, Climate Pro and InsulSafe SP charts, and closed-cell spray foam at R-7.4 per inch is about 6.6 inches.
How thick is R-49 batt insulation?
R-49 fiberglass batt insulation is 14 inches thick as a single batt, per the Owens Corning PINK Next Gen data sheet. Stacking an R-38 batt (12 inches) and an R-13 batt (3.5 inches) gives R-51 at 15.5 inches. ROCKWOOL Comfortbatt mineral wool reaches R-51 at 13 inches with R-38 (9.5 inches) plus R-13 (3.5 inches).
How many inches of blown insulation is R-49?
R-49 needs 13.68 inches of settled blown cellulose (15.20 inches installed) on Greenfiber’s INS541LD chart, or 17 to 18.25 inches of blown fiberglass on the Owens Corning AttiCat, Johns Manville Climate Pro and CertainTeed InsulSafe SP charts. The FTC R-value Rule (16 CFR 460.12) requires each bag to print the minimum settled thickness for R-49.
Is R-49 enough for an attic?
R-49 meets the 2021 IECC attic minimum for climate zones 2 and 3. Zones 4 through 8 need R-60 under the 2021 IECC, although the 2018 IECC, still enforced in many places, required R-49 there. ENERGY STAR recommends R-60 for uninsulated attics in zones 4 to 8. Confirm the code edition your building department enforces.
Can R-49 fit in a 2×10 or 2×12 joist?
Not without mounding above the framing. A 2×10 joist is 9.25 inches deep and a 2×12 is 11.25 inches, while a 14-inch R-49 batt or 13.68 inches of settled cellulose sits above both. That is normal on an attic floor. In a shallow rafter cavity, closed-cell spray foam at R-7.4 per inch reaches R-49 in about 6.6 inches.
How many bags of blown-in insulation for R-49 per 1,000 sq ft?
The maker charts list 25 bags of Owens Corning AttiCat, 22.4 bags of Johns Manville Climate Pro B-7700, or 23.5 bags of CertainTeed InsulSafe SP per 1,000 sq ft at R-49. Bag counts differ by product and blowing machine, so use the chart printed on the bag you buy.