Building thermal envelope opaque assemblies intended to comply on an assembly U-, C- or F-factor basis shall have a U-, C- or F-factor not greater than that specified in Table C402.1.4. Commercial buildings or portions of commercial buildings enclosing Group R occupancies shall use the U-, C- or F-factor from the “Group R” column of Table C402.1.4. Commercial buildings or portions of commercial buildings enclosing occupancies other than Group R shall use the U-, C- or F-factor from the “All other” column of Table C402.1.4. The C-factor for the below-grade exterior walls of the building envelope, as required in accordance with Table C402.1.4, shall extend to a depth of 10 feet (3048 mm) below the outside finished ground level, or to the level of the lowest floor, whichever is less. Opaque swinging doors shall comply with Table C402.1.4 and opaque non-swinging doors shall comply with Table C402.1.3.
OPAQUE THERMAL ENVELOPE ASSEMBLY MAXIMUM REQUIREMENTS, U-FACTOR METHODa, b
| CLIMATE ZONE | 1 | 2 | 3 | 4 EXCEPT MARINE | 5 AND MARINE 4 | 6 | 7 | 8 | ||||||||
| All other | Group R | All other | Group R | All other | Group R | All other | Group R | All other | Group R | All other | Group R | All other | Group R | All other | Group R | |
| Roofs | ||||||||||||||||
| Insulation entirely above roof deck | U-0.048 | U-0.039 | U-0.039 | U-0.039 | U-0.039 | U-0.039 | U-0.032 | U-0.032 | U-0.032 | U-0.032 | U-0.032 | U-0.032 | U-0.028 | U-0.028 | U-0.028 | U-0.028 |
| Metal buildings | U-0.044 | U-0.035 | U-0.035 | U-0.035 | U-0.035 | U-0.035 | U-0.035 | U-0.035 | U-0.035 | U-0.035 | U-0.031 | U-0.031 | U-0.029 | U-0.029 | U-0.029 | U-0.029 |
| Attic and other | U-0.027 | U-0.027 | U-0.027 | U-0.027 | U-0.027 | U-0.027 | U-0.027 | U-0.027 | U-0.027 | U-0.021 | U-0.021 | U-0.021 | U-0.021 | U-0.021 | U-0.021 | U-0.021 |
| Walls, above grade | ||||||||||||||||
| Mass | U-0.151 | U-0.151 | U-0.151 | U-0.123 | U-0.123 | U-0.104 | U-0.104 | U-0.090 | U-0.090 | U-0.080 | U-0.080 | U-0.071 | U-0.071 | U-0.061 | U-0.061 | U-0.061 |
| Metal building | U-0.079 | U-0.079 | U-0.079 | U-0.079 | U-0.079 | U-0.052 | U-0.052 | U-0.052 | U-0.052 | U-0.052 | U-0.052 | U-0.052 | U-0.052 | U-0.039 | U-0.052 | U-0.039 |
| Metal framed | U-0.077 | U-0.077 | U-0.077 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.057 | U-0.064 | U-0.052 | U-0.045 | U-0.045 |
| Wood framed and other c | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.064 | U-0.051 | U-0.051 | U-0.051 | U-0.051 | U-0.036 | U-0.036 |
| Walls, below grade | ||||||||||||||||
| Below-grade wallc | C-1.140e | C-1.140e | C-1.140e | C-1.140e | C-1.140e | C-1.140e | C-0.119 | C-0.119 | C-0.119 | C-0.119 | C-0.119 | C-0.119 | C-0.092 | C-0.092 | C-0.092 | C-0.092 |
| Floors | ||||||||||||||||
| Massd | U-0.322e | U-0.322e | U-0.107 | U-0.087 | U-0.076 | U-0.076 | U-0.076 | U-0.074 | U-0.074 | U-0.064 | U-0.064 | U-0.057 | U-0.055 | U-0.051 | U-0.055 | U-0.051 |
| Joist/framing | U-0.066e | U-0.066e | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 | U-0.033 |
| Slab-on-grade floors | ||||||||||||||||
| Unheated slabs | F-0.73e | F-0.73e | F-0.73e | F-0.73e | F-0.73e | F-0.73e | F-0.54 | F-0.54 | F-0.54 | F-0.54 | F-0.54 | F-0.52 | F-0.40 | F-0.40 | F-0.40 | F-0.40 |
| Heated slabsf | F-0.70 | F-0.70 | F-0.70 | F-0.70 | F-0.70 | F-0.70 | F-0.65 | F-0.65 | F-0.65 | F-0.65 | F-0.58 | F-0.58 | F-0.55 | F-0.55 | F-0.55 | F-0.55 |
| Opaque doors | ||||||||||||||||
| Swinging | U-0.61 | U-0.61 | U-0.61 | U-0.61 | U-0.61 | U-0.61 | U-0.61 | U-0.61 | U-0.37 | U-0.37 | U-0.37 | U-0.37 | U-0.37 | U-0.37 | U-0.37 | U-0.37 |
For SI: 1 pound per square foot = 4.88 kg/m2, 1 pound per cubic foot = 16 kg/m3.
ci = Continuous insulation, NR = No requirement, LS = Liner system.
- Use of Opaque assembly U-factors, C-factors, and F-factors from ANSI/ASHRAE/IESNA 90.1 Appendix A shall be permitted, provided the construction, excluding the cladding system on walls, complies with the appropriate construction details from ANSI/ASHRAE/ISNEA 90.1 Appendix A.
- Opaque assembly U-factors based on designs tested in accordance with ASTM C1363 shall be permitted. The R-value of continuous insulation shall be permitted to be added to or subtracted from the original tested design.
- Where heated slabs are below grade, below-grade walls shall comply with the F-factor requirements for heated slabs.
“Mass floors” shall include floors weighing not less than:
- 35 pounds per square foot of floor surface area; or
- 25 pounds per square foot of floor surface area where the material weight is not more than 120 pounds per cubic foot.
- These C-, F- and U-factors are based on assemblies that are not required to contain insulation.
- Evidence of compliance with the F -factors indicated in the table for heated slabs shall be demonstrated by the application of the unheated slab F-factors and R-values derived from ASHRAE 90.1 Appendix A.
U-factors of walls with cold-formed steel studs shall be permitted to be determined in accordance with Equation 4-1:
where:
| Rs | = | The cumulative R-value of the wall components along the path of heat transfer, excluding the cavity insulation and steel studs. |
| ER | = | The effective R-value of the cavity insulation with steel studs. |
EFFECTIVE R-VALUES FOR STEEL STUD WALL ASSEMBLIES
| NOMINAL STUD DEPTH (inches) | SPACING OF FRAMING (inches) | CAVITY R-VALUE (insulation) | CORRECTION FACTOR (Fc) | EFFECTIVE R-VALUE (ER) (Cavity R-Value × Fc) |
| 31/2 | 16 | 13 | 0.46 | 5.98 |
| 15 | 0.43 | 6.45 | ||
| 31/2 | 24 | 13 | 0.55 | 7.15 |
| 15 | 0.52 | 7.80 | ||
| 6 | 16 | 19 | 0.37 | 7.03 |
| 21 | 0.35 | 7.35 | ||
| 6 | 24 | 19 | 0.45 | 8.55 |
| 21 | 0.43 | 9.03 | ||
| 8 | 16 | 25 | 0.31 | 7.75 |
| 24 | 25 | 0.38 | 9.50 |