The building envelope and its associated assemblies and materials shall meet the provisions of this section.
Where:
Uo = the area-weighted average thermal transmittance of the gross area of the building envelope; i.e., the exterior wall assembly including fenestration and doors, the roof and ceiling assembly, and the floor assembly, Btu/(h·ft2·°F)
Ao = the gross area of the building envelope, ft2
Ui = the thermal transmittance of each individual path of the building envelope, i.e., the opaque portion or the fenestration, Btu/(h·ft2·°F)
Ui = 1/Ri (where Ri is the total resistance to heat flow of an individual path through the building envelope)
Ai = the area of each individual element of the building envelope, ft2
The thermal transmittance of each component of the building envelope shall be determined with due consideration of all major series and parallel heat flow paths through the elements of the component and film coefficients and shall account for any compression of insulation. The thermal transmittance of opaque elements of assemblies shall be determined using a series path procedure with corrections for the presence of parallel paths within an element of the envelope assembly (such as wall cavities with parallel paths through insulation and studs). The thermal performance of adjacent ground in below-grade applications shall be excluded from all thermal calculations.
Where:
Rt = the total resistance of the envelope assembly
Ri = the resistance of the series elements (for i = 1 to n) excluding the parallel path element(s)
Re = the equivalent resistance of the element containing the parallel path (R-value of insulation * Fc). Values for Fc and equivalent resistances shall be taken from Tables 402.1.2.1a or b.
Table 402.1.2.1a-Parallel Path Correction Factors-Metal Roof Trusses Spaced 4 ft. o.c. or Greater That Penetrate the Insulation
Effective framing cavity R-values | Correction factor Fc | Equivalent resistance Re1 |
R-0 | 1.00 | R-0 |
R-5 | 0.96 | R-4.8 |
R-10 | 0.92 | R-9.2 |
R-15 | 0.88 | R-13.2 |
R-20 | 0.85 | R-17.0 |
R-25 | 0.81 | R-20.3 |
R-30 | 0.79 | R-23.7 |
R-35 | 0.76 | R-26.6 |
R-40 | 0.73 | R-29.2 |
R-45 | 0.71 | R-32.0 |
R-50 | 0.69 | R-34.5 |
R-55 | 0.67 | R-36.0 |
1 Based on 0.66-inch-diameter cross members every one foot.
Table 402.1.2.1b-Parallel Path Correction Factors-Metal Framed Walls With Studs 16 Ga. or Lighter
Size of members | Spacing of framing, in. | Cavity insulation R-Value | Correction factor Fc | Equivalent resistance Re |
2 * 4 | 16 O.C. | R-11 R-13 R-15 | 0.50 0.46 0.43 | R-5.5 R-6.0 R-6.4 |
2 * 4 | 24 O.C. | R-11 R-13 R-15 | 0.60 0.55 0.52 | R-6.6 R-7.2 R-7.8 |
2 * 6 | 16 O.C. | R-19 R-21 | 0.37 0.35 | R-7.1 R-7.4 |
2 * 6 | 24 O.C. | R-19 R-21 | 0.45 0.43 | R-8.6 R-9.0 |
2 * 8 | 16 O.C. | R-25 | 0.31 | R-7.8 |
2 * 8 | 24 O.C. | R-25 | 0.38 | R-9.6 |
Where:
Uof = the overall thermal transmittance of the fenestration assemblies, including the center-of-glass, edge-of-glass, and frame components, Btu/(h·ft2·°F)
i = numerical subscript (1, 2, . . .n) refers to each of the various fenestration types present in the wall
n = the number of fenestration assemblies in the wall assembly
Ucg = the thermal transmittance of the center-of-glass area, Btu/(h·ft2·°F)
Acg = the center of glass area, that is the overall visible glass area minus the edge-of-glass area, ft2
Ueg = the thermal transmittance of the edge of the visible glass area including the effects of spacers in multiple glazed units, Btu/(h·ft2·°F)
Aeg = the edge of the visible glass area, that is the 2.5 in. perimeter band adjacent to the frame, ft2
Uf = the thermal transmittance of the frame area, Btu/(h·ft2·°F)
Af = the frame area that is the overall area of the entire glazing product minus the center-of-glass area and minus the edge-of-glass area, ft2
Table 402.2.1-Air Leakage for Fenestration and Doors Maximum Allowable Infiltration Rate
Component | Reference standard | cfm/lin ft Sash crack or cfm/ft2 of area |
Fenestration | ||
Aluminum: | ||
Operable | RS-11* | 0.37 cfm/lin ft. |
Jalousie | RS-11* | 1.50 cfm/ft2. |
Fixed | RS-11* | 0.15 cfm/ft2. |
Poly Vinyl Chloride (PVC): | ||
Prime Windows | RS-12* | 0.37 cfm/ft2. |
Wood: | ||
Residential | RS-13* | 0.37 cfm/ft2. |
Light Commercial | RS-13* | 0.25 cfm/ft2. |
Heavy Commercial | RS-13* | 0.15 cfm/ft2. |
Sliding Glass Doors: | ||
Aluminum | RS-11* | 0.37 cfm/ft2. |
PVC | RS-12* | 0.37 cfm/lin ft. |
Doors-Wood: | ||
Residential | RS-14* | 0.34 cfm/ft2. |
Light Commercial | RS-14* | 0.25 cfm/ft2. |
Heavy Commercial | RS-14* | 0.10 cfm/ft2. |
Commercial Entrance Doors | RS-10* | 1.25 cfm/ft2. |
Residential Swinging Doors | RS-10* | 0.50 cfm/ft2. |
Wall Sections Aluminum | RS-10* | 0.06 cfm/ft2. |
NOTE: [The "Maximum Allowable Infiltration Rates" are from current standards to allow the use of available products.]
* Incorporated by reference, see § 434.701 .
Exceptions are as follows: Outside air intakes, exhaust outlets, relief outlets, stair shaft, elevator shaft smoke relief openings, and other similar elements shall comply with subsection 403.
(b) When more than one condition exists, area weighted averages shall be used. This requirement shall apply to all thermal transmittances, shading coefficients, projection factors, and internal load densities rounded to the same number of decimal places as shown in the respective table.
402.4.1.1 Opaque Walls. The weighted average thermal transmittance (U-value) of opaque wall elements shall be less than the values in Table 402.4.1.1. For mass walls (HC [GREATER THAN EQUAL TO]5), criteria are presented for low and high window/wall ratios and the criteria shall be determined by interpolating between these values for the window/wall ratio of the building.
402.4.1.2 Fenestration. The design of the fenestration shall meet the criteria of Table 402.4.1.2. When the fenestration columns labeled "Perimeter Daylighting" are used, automatic daylighting controls shall be installed in the perimeter daylighted zones of the building. These daylighting controls shall be capable of reducing electric lighting power to at least 50% of full power. Only those shading or lighting controls for perimeter daylighting that are shown on the plans shall be considered. The column labeled "VLT [GREATER THAN]= SC" shall be used only when the shading coefficient of the glass is less than its visible light transmittance.
Appendix A
The example Alternate Component Package tables illustrate the requirements of subsections 434.301.1 , 434.402.3.1 , 434.402.3.2 , 434.402.4.1.1 and 434.402.4.1.2 . Copies of specific tables contained in this appendix A can be obtained from the Energy Code for Federal Commercial Buildings, Docket No. EE-RM-79-112-C, EE-43, Office of Building Research and Standards, U.S. Department of Energy, Room 1J-018, 1000 Independence Avenue, SW., Washington, DC 20585, (202) 586-9127.
Table 402.4.2-EQUIP Default Values for ENVSTD24
Occupancy | Default equipment power density1 | Default occupant load adjustment1 | Default adjusted equipment power density |
Assembly | 0.25 | 0.75 | 1.00 |
Health/Institutional | 1.00 | -0.26 | 0.74 |
Hotel/Motel | 0.25 | -0.33 | 0.00 |
Warehouse/Storage | 0.10 | -0.60 | 0.00 |
Multi-Family High Rise | 0.75 | N/A | 0.00 |
Office | 0.75 | -0.35 | 0.40 |
Restaurant | 0.10 | 0.07 | 0.17 |
Retail | 0.25 | -0.38 | 0.00 |
School | 0.50 | 0.30 | 0.80 |
1 Defaults as defined in Section 8.6.10.5 , Table 8-4, and Sections 8.6.10.6 and 13.7.2.1 , Table 13-2 from RS-1 (incorporated by reference, see § 434.701 ).
10 C.F.R. §434.402