Table 5.

Thermal transmittance of window structures.

Reinforcement material	Window section	R-value [(m2·℃)/W]	*U-value [W/(m2·K)]	*U-factor [Btu/(h·ft2·℉)]
Steel	Sash	0.678	1.47	0.26
	Frame	0.638	1.57	0.28
	Glazing	0.648	1.54	0.27
	Glazing edge	0.538	1.86	0.33
	Whole window	0.647	1.55	0.27
GF/PP	Sash	0.778	1.29	0.23
	Frame	0.738	1.36	0.24
	Glazing	0.658	1.52	0.27
	Glazing edge	0.548	1.82	0.32
	Whole window	0.681	1.47	0.26

*Calculated from R-value.