Glossary - R

 

A Glossary of window terminology

 

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Rail

The horizontal top and bottom members of a window sash or door panel. 

 

Rough opening

The framed opening in a wall into which a window or door unit is to be installed. 

R-value
A measure of the resistance of a glazing material or fenestration assembly to heat flow. It is the inverse of the U-factor (R = 1/U) and is expressed in units of hr-sq ft-ºF/Btu. A high-R-value window has a greater resistance to heat flow and a higher insulating value than one with a low R-value.

Radiation
The transfer of heat in the form of electromagnetic waves from one separate surface to another. Energy from the sun reaches the earth by radiation and a person’s body can lose heat to a cold window or skylight surface in a similar way.

Relative Humidity
The ratio of the amount of water vapor in the air compared to the maximum amount that could be present (usually expressed in a percentage); 100 percent is when the air is totally saturated with moisture.  

Removable Operator Cover
A plastic or metal cover which conceals the operating hardware on a casement or awning window.  

Reveal
The space between the window sash or door panel and the frame.  

Riser
The structural component fixed to the bottom of the stationary sash in a horizontal sliding window.

Roto-Operator
A window-opening mechanism that has a handle that turns in a circular pattern; used on awning windows.