The transmission of energy through space without heating the air between, as in Solar Radiation.
The horizontal members of a window sash or door panel.
Window or door glass coated to reflect radiation striking the surface of the glass.
The opening left in a frame wall to receive a window or door unit.
The horizontal rough framing member, usually two inches by four inches, which forms the bottom of the rough opening. It is toe-nailed into the jack studs and is supported by cripples.
R-VALUE (THERMAL RESISTANCE)
A measure of resistance to heat flow of a material or construction; a higher value indicates a better heat insulating property. The R-value of an ordinary single-pane sash with a 15 mph wind on one side is about 0.9.