# A9 Determination of Alternate Assembly U-Factors, C-Factors, F-Factors, or Heat Capacities

Component *U-factors* for other *opaque* assemblies shall be determined in accordance with Section A9 only if approved by the *building official* in accordance with Section A1.2. The procedures required for each *class of construction* are specified in Section A9.2. Testing shall be performed in accordance with Section A9.3. Calculations shall be performed in accordance with Section A9.4.

Two- or three-dimensional finite difference and finite volume computer models shall be an acceptable alternative method to calculating the thermal performance values for all assemblies and constructions listed below. The following procedures shall also be permitted to determine all alternative *U-factors, F-factors*, and *C-factors:*

- Roofs
*Roofs with insulation entirely above deck*: Testing or series calculation method.*Metal building roofs:*Testing, or for single-layer and double-layer*systems*, calculation method in Section A9.4.6.- Attic
*roofs*, wood joists: Testing or parallel path calculation method. - Attic
*roofs, steel joists:*Testing or parallel path calculation method using the insulation/framing layer adjustment factors in Table A9.2-1 or modified zone calculation method. - Attic
*roofs*, concrete joists: Testing or parallel path calculation method if concrete is solid and uniform, or isothermal planes calculation method if concrete has hollow sections. - Other attic
*roofs*and other*roofs:*Testing or two-dimensional calculation method.

- Above-Grade Walls
*Mass walls:*Testing or isothermal planes calculation method or two-dimensional calculation method. The parallel path calculation method is not acceptable.*Metal building walls:*Testing, or for single-layer compressed, single-layer in cavity, double-layer*systems*, and*continuous insulation*, calculation method in Section A9.4.6.*Steel-framed walls:*Testing or parallel path calculation method using the insulation/framing layer adjustment factors in Table A9.2-2 or the modified zone method.- Wood-framed
*walls:*Testing or parallel path calculation method. - Other
*walls:*Testing or two-dimensional calculation method.

- Below-Grade Walls
*Mass walls:*Testing or isothermal planes calculation method or two-dimensional calculation method. The parallel path calculation method is not acceptable.- Other
*walls:*Testing or two-dimensional calculation method.

- Floors
*Mass floors:*Testing or parallel path calculation method if concrete is solid and uniform or isothermal planes calculation method if concrete has hollow sections.*Steel-joist floors:*Testing or modified zone calculation method.*Wood-joist floors:*Testing or parallel path calculation method or isothermal planes calculation method.- Other
*floors:*Testing or two-dimensional calculation method.

- Slab-on-Grade Floors
- No testing or calculations allowed.

**Table A9.2-1 Effective Insulation/Framing Layer R-Values for Roof and Floor Insulation Installed Between Metal Framing (4 ft on Center)**

Rated R-Value of Insulation | Correction Factor | Framing/Cavity R-Value | Rated R-Value of Insulation | Correction Factor | Framing/Cavity R-Value |
---|---|---|---|---|---|

0.00 | 1.00 | 0.00 | 20.00 | 0.85 | 17.00 |

4.00 | 0.97 | 3.88 | 21.00 | 0.84 | 17.64 |

5.00 | 0.96 | 4.80 | 24.00 | 0.82 | 19.68 |

8.00 | 0.94 | 7.52 | 25.00 | 0.81 | 20.25 |

10.00 | 0.92 | 9.20 | 30.00 | 0.79 | 23.70 |

11.00 | 0.91 | 10.01 | 35.00 | 0.76 | 26.60 |

12.00 | 0.90 | 10.80 | 38.00 | 0.74 | 28.12 |

13.00 | 0.90 | 11.70 | 40.00 | 0.73 | 29.20 |

15.00 | 0.88 | 13.20 | 45.00 | 0.71 | 31.95 |

16.00 | 0.87 | 13.92 | 50.00 | 0.69 | 34.50 |

19.00 | 0.86 | 16.34 | 55.00 | 0.67 | 36.85 |

**Table A9.2-2 Effective Insulation/Framing Layer R-Values for Wall Insulation Installed Between Steel Framing**

Nominal Depth of Cavity, in. | Actual Depth of Cavity, in. | Rated R-Value of Air space or Insulation | Effective Framing/Cavity R-Value at 16 in. on Center | Effective Framing/Cavity R-Value at 24 in. on Center |
---|---|---|---|---|

Empty Cavity, No Insulation | ||||

4 | 3.5 | R-0.91 | 0.79 | 0.91 |

Insulated Cavity | ||||

4 | 3.5 | R-11 | 5.5 | 6.6 |

4 | 3.5 | R-13 | 6.0 | 7.2 |

4 | 3.5 | R-15 | 6.4 | 7.8 |

6 | 6.0 | R-19 | 7.1 | 8.6 |

6 | 6.0 | R-21 | 7.4 | 9.0 |

8 | 8.0 | R-25 | 7.8 | 9.6 |

If *building material R-values* or thermal conductivities are determined by testing, one of the following test procedures shall be used:

- ASTMC177
- ASTMC518
- ASTMC1363

For concrete, the oven-dried conductivity shall be multiplied by 1.2 to reflect the moisture content as typically installed.

If assembly *U-factors* are determined by testing, ASTM C1363 test procedures shall be used.

Product samples tested shall be production-line material or representative of material as purchased by the consumer or contractor. If the assembly is too large to be tested at one time in its entirety then either a representative portion shall be tested or different portions shall be tested separately and a weighted average determined. To be representative, the portion tested shall include edges of panels, joints with other panels, typical framing percentages, and thermal bridges.

The following procedures and assumptions shall be used for all calculations. *R-values* for air films, air *spaces*, insulation, and *building materials* shall be taken from Sections A9.4.1 through A9.4.4, respectively. In addition, the appropriate assumptions listed in Sections A2 through A8, including framing factors, shall be used.

Exterior surfaces are areas exposed to the wind.

Semiexterior surfaces are protected surfaces that face attics, crawlspaces, and parking garages with natural or mechanical *ventilation.*

Interior surfaces are surfaces within *enclosed spaces.*

### Related Code Sections

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*alternative*

*U*-

*factors*,

*F*-

*factors*, and

*C*-

*factors*: Roofs Roofs with insulation entirely above deck ...

*assemblies*shall be calculated using published values for the unit weight and specific

*heat*of all building material components ...

*determined*by testing, one of the following test procedures shall be used: ASTMC177 ...

*c*= R-value of the compressed insulation, h•ft 2 •°

*F*/Btu Step 4:

*Determine*the overall area-weighted

*U*-

*factor*...

*heat*flow up 0.92 Interior horizontal surfaces,

*heat*flow down 0.68 ...