Section C304 Materials Testing and Thermal Properties
R-values for building materials used to demonstrate code compliance with Chapter C4 shall be taken from ASHRAE 90.1 Normative Appendix A, from manufacturer's product literature or from other nationally recognized engineering sources. Assembly U-factor calculations shall follow the procedure(s) detailed in Section C304.3 or be tested in accordance with procedure(s) described in Section C304.2.
Concrete block R-values shall be calculated using the isothermal planes method or a two-dimensional calculation program, thermal conductivities from ASHRAE 90.1 Normative Appendix A and dimensions from ASTM C90. The parallel path calculation method is not acceptable.
Exception: R-values for building materials or thermal conductivities determined from testing in accordance with Section C304.2.
If building material R-values or thermal conductivities are determined by testing, one of the following test procedures shall be used:
- ASTM C177
- ASTM C236
- ASTM C518
For concrete, the oven-dried conductivity shall be multiplied by 1.2 to reflect the moisture content as typically installed.
If the building official determines that the proposed construction assembly is not adequately represented in the appropriate table of ASHRAE 90.1 Normative Appendix A, the applicant shall determine appropriate values for the assembly using the assumptions in ASHRAE 90.1 Normative Appendix A. An assembly is deemed to be adequately represented if:
- the interior structure, hereafter referred to as the base assembly, for the class of construction is the same as described in Normative Appendix A and
- changes in exterior or interior surface building materials added to the base assembly do not increase or decrease the R-value by more than 2 from that indicated in the descriptions in ASHRAE 90.1 Normative Appendix A.
Insulation, including insulated sheathing, is not considered a building material.