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 C403.10.1 or C403.10.2.
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 setpoint 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 comply with 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 shall be not less than that specified in Table C402.1.3. 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.
OPAQUE THERMAL ENVELOPE INSULATION COMPONENT MINIMUM REQUIREMENTS, R-VALUE METHODa, i
| 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 + R11 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 | ||||||||||||||||
| Massg | 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 slabsh | R-7.5 for 12" below + R-5 full slab | R-7.5 for 12" below + R-5 full slab | R-7.5 for 12" below + R-5 full slab | R-7.5 for 12" below + R-5 full slab | R-10 for 24" below + R-5 full slab | R-10 for 24" below + R-5 full slab | R-15 for 24" below + R-5 full slab | R-15 for 24" below + R-5 full slab | R-15 for 36" below + R-5 full slab | R-15 for 36" below + R-5 full slab | R-15 for 36" below + R-5 full slab | R-20 for 48" below + R-5 full slab | R-20 for 48" below + R-5 full slab | R-20 for 48" below + R-5 full slab | R-20 for 48" below + R-5 full slab | R-20 for 48" below + R-5 full slab |
| 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 C90, 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 be in accordance with Section C402.2.3.
- Steel floor joist systems shall be insulated to R-38.
- "Mass walls" shall be in accordance with Section C402.2.2.
- The first value is for perimeter insulation and the second value is for slab insulation. Perimeter insulation is not required to extend below the bottom of the slab.
- Not applicable to garage doors. See Table C402.1.4.