Guide to the Glass

Guide to the Glass

Guide to the Glass

Do you know cladding from a casemaster? What about muntin vs. mulling? Familiarize yourself with some of the following basic window anatomy and terminology, courtesy of Marvin Windows and Doors.

Window Anatomy

Cladding –The exterior covering of the window. Marvin’s clad exterior is made of extruded aluminum with a thick, commercial-grade, durable finish.

Frame – The stationary portion of a window installed into the rough opening of a wall that encloses the sash (operating and/or stationary). Consists of the header, jamb and sill.

Header – The top horizontal component of the frame.

Jamb – The left or right vertical side component of the frame.

Sill –The bottom horizontal component of a window frame.

Glazing – The actual glass (single or insulating) installed in a sash or a panel.

Single – Glazing with one sheet of glass.

Insulating – Two sheets of glass hermetically sealed with space between the panes. Argon gas may fill the space for added insulating properties.

Hardware – The operating components of your window: locks, handles, hinges, etc.

Lite – A single area of glass within the sash or a pattern of divided lites.

Divided Lites – Division of light by the use of muntin bars.

Muntins – The bars that divide the glass into lites.

Authentic Divided Lites (ADLs) – Single or insulating glass, individually glazed between the muntin bars.

Simulated Divided Lites (SDLs) – Muntins permanently adhered to the interior and exterior of the glass.

Grilles – Wood muntins fastened to the interior of the sash to create the effect of divided lites; removable for easy glass cleaning.

Grilles Between Glass (GBGs) – Aluminum flat or contour bars that divide the glass visually. Because the grille is between the glass, grilles do not dislodge or become damaged. Cleaning is easy without small panes of individual lites.

Spacer Bar – Tiny aluminum bars inserted between SDL muntins to emulate ADL.

Sash – The glass-and-wood operating or stationary portion of a window, separate from the frame. Consists of stiles and rails.

Stiles – Vertical sides of the window sash.

Rails – Horizontal sides of the sash.

Window Styles from Marvin

Ultimate Double Hung – A window with two sash that slide up and down.

Glider – A window with a horizontally gliding sash.

Casemaster – A window that opens and closes using a folding handle, swinging out from the side.

Multiple Assembly – Windows that are connected to form the appearance of a single window. Simple window shapes can be put together to create nearly limitless window combinations. Examples are Bays and Bows.

Bay – Multiple assembly windows made from operating and/or stationary Casemaster or Ultimate Double Hung windows.

Bow – Windows made from the same components as Bay windows, but the windows are arched to create a bow.

Round Top –Available in a variety of full, half, and quarter rounds as well as eyebrows, ellipticals, inverted corners, ovals, gothic heads, and more. Can be stationary or operable.

Weatherstripping – A strip of resilient material designed to seal the sash and frame members in order to reduce air and water infiltration.


Argon Gas – A colorless, odorless gas used to fill the airspace between panes of insulating glass. The addition of argon gas greatly increases the thermal performance of a window by minimizing heat transfer.

Low E II Glass – Low E stands for “low emissivity” and is designed to improve thermal performance. Low E II glass is coated twice with microscopic metal or metallic oxide layers to reflect or absorb the sun’s warmth, as well as reduce the damage from ultraviolet (UV) rays.

Mulling – The act of attaching two or more units together.

Design Pressure (DP) – A design pressure rating, as created by the American Architectural Manufacturers Association (AAMA)/Window and Door Manufacturers Association (WDMA) 101/I.S.2-97, is a measure of the amount of pressure a window or door is designed to withstand when closed and locked.Each DP rating also establishes other performance factors such as structural pressure, water penetration and air infiltration.The higher a DP number a window or door has, the better the performance.As a frame of reference: DP 40 means that a window or door is tested to 60 pounds per square foot equal to a 155 m.p.h. (250 km/hr) wind and must withstand water penetration under conditions equal to 8 inches (20cm) of rain per hour driven by 50 m.p.h. (80 km/hr) winds.

R-Value – The resistance a material has to heat flow. Higher numbers indicate greater insulating capabilities.