C402.1.4 Assembly U-factor, C-Factor or F-Factor-Based Method
Building thermal envelope opaque assemblies shall meet the requirements of Sections C402.2 and C402.4 based on the climate zone specified in Chapter 3. 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
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 | ||||||||||||||||
| Massg | 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-0.071 | 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-0.064 | U-0.064 | U-0.052 | U-0.064 | U-0.045 |
| Wood framed and otherc | 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-0.064 | 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-1.02 0.74 | F-1.02 0.74 | F-1.02 0.74 | F-1.02 0.74 | F-0.90 0.74 | F-0.90 0.74 | F-0.86 0.64 | F-0.86 0.64 | F-0.79 0.64 | F-0.79 0.64 | F-0.79 0.55 | F-0.69 0.55 | F-0.69 0.55 | F-0.69 0.55 | F-0.69 0.55 | F-0.69 0.55 |
| Opaque doors | ||||||||||||||||
| Swinging door | 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 |
| Garage door <14% glazing | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 | U-0.31 |
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.
- Where assembly U-factors, C-factors, and F-factors are established in ANSI/ASHRAE/IESNA 90.1 Appendix A, such opaque assemblies shall be a compliance alternative where those values meet the criteria of this table, and provided that the construction, excluding the cladding system on walls, complies with the appropriate construction details from ANSI/ASHRAE/ISNEA 90.1 Appendix A.
- Where U-factors have been established by testing in accordance with ASTM C1363, such opaque assemblies shall be a compliance alternative where those values meet the criteria of this table. 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 U-factor requirements for above-grade mass walls.
- "Mass floors" shall be in accordance with Section C402.2.3.
- These C-, F- and U-factors are based on assemblies that are not required to contain insulation.
- The first value is for perimeter insulation and the second value is for full slab insulation.
- "Mass walls" shall be in accordance with Section C402.2.2.
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 as specified in Table C402.1.4.1.
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 |