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.]