R-38 at 9.5 in. in 23 in. × 47 in. wood 24 OC module
Key features
Flexible-edge semi-rigid stone wool for wide stud bays
Noncombustible fiber with 0/0 ASTM E84 indices per TDS
Technical specifications
| R-Value | 38.0 |
|---|---|
| Thickness | 9.5 in |
| Width | 23.0 in |
| Length | 47.0 in |
| Coverage | 22.5 sq ft/pack |
| Material | Stone wool (basalt and recycled steel slag) |
| Fire rating | Noncombustible per ASTM E136; Flame Spread 0 / Smoke Developed 0 per ASTM E84 on ROCKWOOL USA Comfortbatt TDS (05-2025). |
| Sound rating | Deep wide-bay fills improve low-frequency absorption versus thin insulation; partition metrics remain assembly-specific. |
| Density | >1.8 lb/ft³ per ASTM C167 on ROCKWOOL USA Comfortbatt TDS (05-2025). |
| Framing width | 24 in. on-center wood stud module (23 in. batt width per USA TDS) |
| Construction type | Wood stud framing |
| Application area | Attic and cathedral ceilings, high-R exterior wood walls at 24 in. o.c., and exposed floors per ROCKWOOL when cavity depth accepts 9.5 in. batts. |
Product details
High-R, wide-bay framing is attractive for cost and speed until insulation detail breaks the thermal plane. RXCB3823 pairs 9.5 in. labeled thickness with the 23 in. width ROCKWOOL assigns to wood studs at 24 in. on center, keeping full-thickness contact without strip-cutting 15.25 in. batts across every bay.
The Comfortbatt USA data sheet (05-2025) documents R-38 at 9.5 in. thickness for appropriate wood-stud products; use the PDF—not marketing blurbs—for code language.
Coordinate structure: deep insulation layers add mass and may influence gypsum screw length, exterior furring, and cladding attachment when CI is outboard.
Reaction to fire and moisture statements follow the Comfortbatt family: noncombustible to ASTM E136, 0/0 to ASTM E84, and published sorption/transmission data for representative configurations. Execution still requires correct WRB and drainage.
Coverage near 22.5 square feet per bag implies more packages per insulated area than R-15 SKUs—plan truck counts and waste realistically.
Reference https://www.rockwool.com/siteassets/o2-rockwool/documentation/technical-data-sheets/residential/comfortbatt-exterior-wood-and-steel-stud-thermal-batt-insulation-techdata-us.pdf on every submittal package.
Documents & certifications
Technical data sheet
Manufacturer-tested R-value, coverage, fire notes, and handling—use for submittals, RFIs, and field QA.
Download PDF (opens in new tab)Certifications & compliance
ASTM C665 Type I compliant, ASTM E136 noncombustible, ASTM E84 flame spread 0 / smoke developed 0 (Note 1 Class A per IBC on TDS), ASTM C518 thermal resistance per published R-thickness table, GREENGUARD Gold per ROCKWOOL Comfortbatt marketing
Frequently asked questions
How does coverage compare to the 15.25 in. R-38 batt?
How does coverage compare to the 15.25 in. R-38 batt?
The 23 in. wide R-38 SKU lists about 22.5 sq ft per bag versus roughly 19.9 sq ft for the 15.25 in. wide R-38 format—pick based on stud spacing and verified field dimensions.
Will this compress into a 2×8 cavity?
Will this compress into a 2×8 cavity?
A nominal 2×8 stud is 7.25 in. deep; a 9.5 in. batt is too thick unless the assembly uses deeper engineered framing or layered details approved by design.
What PPE is recommended?
What PPE is recommended?
Follow ROCKWOOL safe-use guidance: gloves, long sleeves, eye protection, and a dust mask are typical minimums when handling mineral wool.
What if batts get wet on site?
What if batts get wet on site?
Brief exposure happens, but saturated batts gain weight and complicate installation; restore drying before enclosure when possible and maintain drainage planes outdoors.