WAC 51-11C-61051. Section A105.1 — General

A105.1 General. Tables A105.1(1), A105.1(2) and A105.1(3) list heat loss coefficients for floors over unconditioned spaces in units of Btu/h • ft 2 • °F. They are derived from procedures listed in the ASHRAE Fundamentals Handbook, assuming an average outdoor temperature of 45°F, an average indoor temperature of 65°F and a crawlspace area of 1350 ft 2 and 100 feet of perimeter. The crawlspace is assumed to be 2.5 feet high, with 24 inches below grade and 6 inches above grade. Table A105.1(1) Default U-factors for Wood-Framed Floors over Vented Crawlspace or Unheated Basement Nominal R-value U-factor Floor Perimeter Post & Beam Joists 0 0 11 19 30 0.112 0.100 0.098 0.093 0.134 0.116 0.114 0.107 11 0 11 0.052 0.048 0.056 0.052 19 0 11 0.038 0.036 0.041 0.038 22 0 11 0.034 0.033 0.037 0.035 25 0 11 0.032 0.031 0.034 0.033 30 0 11 0.028 0.027 0.029 0.028 38 0 11 0.024 0.024 0.025 0.024 Nominal R-value U-factor Floor Perimeter Post & Beam Joists 0 0 11 19 30 0.112 0.100 0.098 0.093 0.134 0.116 0.114 0.107 11 0 11 0.052 0.048 0.056 0.052 19 0 11 0.038 0.036 0.041 0.038 22 0 11 0.034 0.033 0.037 0.035 25 0 11 0.032 0.031 0.034 0.033 30 0 11 0.028 0.027 0.029 0.028 38 0 11 0.024 0.024 0.025 0.024 Table A105.1(2) Default U-factors for Wood-Framed Floors over Heated Plenum Crawlspaces Nominal R-value Perimeter U-factor 11 0.085 19 0.075 30 0.069 Nominal R-value Perimeter U-factor 11 0.085 19 0.075 30 0.069 Note: Crawlspaces used as heated plenums have approximately 30 percent higher heat loss rate than unvented crawlspaces with the same assumed ACH. Default U-factors in Table A105.1(2) reflect this higher rate of heat loss. Table A105.1(3) Default U-factors for Exposed Floors Nominal R-value U-factor Concrete Wood Joist Metal Joist R-11 0.077 0.088 0.14 R-15 0.059 0.076 0.12 R-19 0.048 0.062 0.11 R-21 0.043 0.057 0.11 R-25 0.037 0.051 0.10 R-30 0.031 0.040 0.09 R-38 0.025 0.034 0.08 Nominal R-value U-factor Concrete Wood Joist Metal Joist R-11 0.077 0.088 0.14 R-15 0.059 0.076 0.12 R-19 0.048 0.062 0.11 R-21 0.043 0.057 0.11 R-25 0.037 0.051 0.10 R-30 0.031 0.040 0.09 R-38 0.025 0.034 0.08