WAC 51-11C-61051:

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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
Nominal R-value	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.]