Section C402 Building Envelope Requirements
Building thermal envelope assemblies for buildings that are intended to comply with the code on a prescriptive basis, in accordance with the compliance path described in Item 2 of Section C401.2, shall comply with the following:
- The opaque portions of the building thermal envelope shall comply with the specific insulation requirements of Section C402.2 and the thermal requirements of either the R-value-based method of Section C402.1.3; the U-, C-and F-factor-based method of Section C402.1.4; or the component performance alternative of Section C402.1.5.
- Roof solar reflectance and thermal emittance shall comply with Section C402.3.
- Fenestration in building envelope assemblies shall comply with Section C402.4.
- Air leakage of building envelope assemblies shall comply with Section C402.5.
Alternatively, where buildings have a vertical fenestration area or skylight area exceeding that allowed in Section C402.4, the building and building thermal envelope shall comply with Section C401.2, Item 1 or Section C401.2, Item 3.
Walk-in coolers, walk-in freezers, refrigerated warehouse coolers and refrigerated warehouse freezers shall comply with Section C403.2.15 or C403.2.16.
The following low-energy buildings, or portions thereof separated from the remainder of the building by building thermal envelope assemblies complying with this section, shall be exempt from the building thermal envelope provisions of Section C402.
- Those with a peak design rate of energy usage less than 3.4 Btu/h • ft2 (10.7 W/m2) or 1.0 watt per square foot (10.7 W/m2) of floor area for space conditioning purposes.
- Those that do not contain conditioned space.
- Greenhouses.
Buildings that comply with the following shall be exempt from the building thermal envelope provisions of this code:
- Are separate buildings with floor area not more than 500 square feet (50 m2).
- Are intended to house electronic equipment with installed equipment power totaling not less than 7 watts per square foot (75 W/m2) and not intended for human occupancy.
- Have a heating system capacity not greater than (17,000 Btu/hr) (5 kW) and a heating thermostat set point that is restricted to not more than 50°F (10°C).
- Have an average wall and roof U-factor less than 0.200 in Climate Zones 1 through 5 and less than 0.120 in Climate Zones 6 through 8.
- Comply with the roof solar reflectance and thermal emittance provisions for Climate Zone 1.
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. For opaque portions of the building thermal envelope intended to comply on an insulation component R-value basis, the R-values for insulation in framing cavities, where required, and for continuous insulation, where required, shall be not less than that specified in Table C402.1.3, based on the climate zone specified in Chapter 3. Commercial buildings or portions of commercial buildings enclosing Group R occupancies shall use the R-values from the "Group R" column of Table C402.1.3. Commercial buildings or portions of commercial buildings enclosing occupancies other than Group R shall use the R-values from the "All other" column of Table C402.1.3. The thermal resistance or R-value of the insulating material installed continuously within or on the below-grade exterior walls of the building envelope required in accordance with Table C402.1.3 shall extend to a depth of not less than 10 feet (3048 mm) below the outside finished ground level, or to the level of the lowest floor of the conditioned space enclosed by the below grade wall, whichever is less. Opaque swinging doors shall comply with Table C402.1.4 and opaque nonswinging doors shall comply with Table C402.1.3.
| 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 | R-20ci | R-25ci | R-25ci | R-25ci | R-25ci | R-25ci | R-30ci | R-30ci | R-30ci | R-30ci | R-30ci | R-30ci | R-35ci | R-35ci | R-35ci | R-35ci |
| Metal buildingsb | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-19 + R-11 LS | R-25 + R-11 LS | R-25 + R-11 LS | R-30 + R-11 LS | R-30 + R-11 LS | R-30 + R-11 LS | R-30 + R-11 LS |
| Attic and other | R-38 | R-38 | R-38 | R-38 | R-38 | R-38 | R-38 | R-38 | R-38 | R-49 | R-49 | R-49 | R-49 | R-49 | R-49 | R-49 |
| Walls, above grade | ||||||||||||||||
| Mass | R-5.7cic | R-5.7cic | R-5.7cic | R-7.6ci | R-7.6ci | R-9.5ci | R-9.5ci | R-11.4ci | R-11.4ci | R-13.3ci | R-13.3ci | R-15.2ci | R-15.2ci | R-15.2ci | R-25ci | R-25ci |
| Metal building | R-13+ R-6.5ci | R-13 + R-6.5ci | R13 + R-6.5ci | R-13 + R-13ci | R-13 + R-6.5ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-13ci | R-13 + R-19.5ci | R-13 + R-13ci | R-13 + R-19.5ci |
| Metal framed | R-13 + R-5ci | R-13 + R-5ci | R-13 + R-5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-7.5ci | R-13 + R-15.6ci | R-13 + R-7.5ci | R-13 + R17.5ci |
| Wood framed and other | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-3.8ci or R-20 | R-13 + R-7.5ci or R-20 + R-3.8ci | R-13 + R-7.5ci or R-20 + R-3.8ci | R-13 + R-7.5ci or R-20 + R-3.8ci | R-13 + R-7.5ci or R-20 + R-3.8ci | R-13 + R-7.5ci or R-20 + R-3.8ci | R13 + R-15.6ci or R-20 + R-10ci | R13 + R-15.6ci or R-20 + R-10ci |
| Walls, below grade | ||||||||||||||||
| Below-grade walld | NR | NR | NR | NR | NR | NR | R-7.5ci | R-7.5ci | R-7.5ci | R-7.5ci | R-7.5ci | R-7.5ci | R-10ci | R-10ci | R-10ci | R-12.5ci |
| Floors | ||||||||||||||||
| Masse | NR | NR | R-6.3ci | R-8.3ci | R-10ci | R-10ci | R-10ci | R-10.4ci | R-10ci | R-12.5ci | R-12.5ci | R-12.5ci | R-15ci | R-16.7ci | R-15ci | R-16.7ci |
| Joist/framing | NR | NR | R-30 | R-30 | R-30 | R-30 | R-30 | R-30 | R-30 | R-30 | R-30 | R-30f | R-30f | R-30f | R-30f | R-30f |
| Slab-on-grade floors | ||||||||||||||||
| Unheated slabs | NR | NR | NR | NR | NR | NR | R-10 for 24" below | R-10 for 24" below | R-10 for 24" below | R-10 for 24" below | R-10 for 24" below | R-15 for 24" below | R-15 for 24" below | R-15 for 24" below | R-15 for 24" below | R-20 for 24" below |
| Heated slabs | R-7.5 for 12" below | R-7.5 for 12" below | R-7.5 for 12" below | R-7.5 for 12" below | R-10 for 24" below | R-10 for 24" below | R-15 for 24" below | R-15 for 24" below | R-15 for 36" below | R-15 for 36" below | R-15 for 36" below | R-20 for 48" below | R-20 for 24" below | R-20 for 48" below | R-20 for 48" below | R-20 for 48" below |
| Opaque doors | ||||||||||||||||
| Nonswinging | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 | R-4.75 |
For SI: 1 inch = 25.4 mm, 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.
- Assembly descriptions can be found in ANSI/ASHRAE/IESNA Appendix A.
- Where using R-value compliance method, a thermal spacer block shall be provided, otherwise use the U-factor compliance method in Table C402.1.4.
- R-5.7ci is allowed to be substituted with concrete block walls complying with ASTM C 90, ungrouted or partially grouted at 32 inches or less on center vertically and 48 inches or less on center horizontally, with ungrouted cores filled with materials having a maximum thermal conductivity of 0.44 Btu-in/h-f2 °F.
- Where heated slabs are below grade, below-grade walls shall comply with the exterior insulation 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.
- Steel floor joist systems shall be insulated to R-38.