PDFWAC 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 • ft2 • °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 ft2 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 | |
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 |
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 |
[Statutory Authority: RCW 19.27A.025, 19.27A.160, and 19.27.074. WSR 16-03-072, § 51-11C-61051, filed 1/19/16, effective 7/1/16. Statutory Authority: RCW 19.27A.020, 19.27A.025 and chapters 19.27 and 34.05 RCW. WSR 13-04-056, § 51-11C-61051, filed 2/1/13, effective 7/1/13.]