Replacement Windows

A WINDOW ON WINDOW LINGO

Case or easing— the frame of trim boards around window opening.

Check rail —the opposing horizontal rails of double-hung sash that meet in the center when the window is closed. Weather stripping is critical here to stop drafts from rising between the two sashes. Modern windows have double-insulated, spring-sealing check rails.

Glazer —an archaic term for window maker and installer.

Frame —the rectangle of stout 1'-thick boards that support the sash, hold the casing, and fit into the "rough opening" in the house framing. Often called a casement. The inner dimensions form the "sash opening."

Jamb —the top and site members of a window frame (the bottom board is the "sill"),

Jamb extension —wood trim used to extend the jamb from a manufactured window to the surface of the house wall. Needed if window is thinner than wall frame/sheathing.

Light —the panes of glass in a window Double-hung windows are designated by the number of lights in upper and lower sashes, as in six-over-six.

Muntins ("mullions" or "muttons")—the rabbeted (grooved) wood strips that separate individual panes of glass in a window sash. These glazing bars have not been structurally needed since the advent of large-size sheet glass, but offer the traditional look of small panes. Simulated muntin grilles can be sandwiched inside multiple-pane insulated-glass assemblies or mounted on the outside.

Rough opening— width and height of the opening in a building's frame into which a window fits.

RA —identifies a listing of the width and height dimensions of a window; abbreviation for rough opening.

Sash— the framework of stiles and rails within which panes of window glass are set.

Shim -thin wedge-shaped boards used to fill spaces between window frames and rough opening; also, the act of installing shims.

Sill —the bottom crosspiece of a window frame. The sill of a double-hung window is of heavier stock and slopes to shed water to the outside.

Stool or stool cap —trim board that caps the sill on the inside of a window frame. "The windowsill" where the cat takes the sun is actually the stool cap,

Air infiltration rate —measurement of the airflow between the window sash and the frame. The lower the better. An honest manufacturer lists the average rate not the best individual unit rate.

Low-E glass —low emissivity glass... has transparent metallic coating that reduces heat loss in winter and heat gain in summer. It also filters out ultraviolet rays.

R value —measurement of the resistance of materials used in window construction to the transfer of heat. The higher the rating the better. Some manu facturers list R values for the frame or glass separate from the overall average.

U value —the converse of R value. A measurement of heat loss through a window. The lower the better.