Glossary - D

A Glossary of window terminology

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Design Pressure

The pressure a product is designed to withstand. This value is a measure of a product’s capacity to withstand the forces of windloading, in both positive and negative directions, while it is closed and locked. 

Dormer

A projection through the slope of a roof for a vertical window. 

Drip cap

Horizontal molding to divert water from the top of a window unit so water drips beyond the outside of the frame. May be metal or wood. 

Dual durometer

A material that has two or more levels of flexibility. An example is the weatherstripping used between the frame and sash of a Pella casement window.

Double Channel Lineal
A siding accessory that joins two soffit panels.

Dado
A groove or rectangular section for receiving the end of a board.  

Daylight Opening
The visible or touchable area of glass in a window or patio door.  

Decorative Entry System
An entryway made up of a door in a frame, one or two sidelights, and a transom.  

Delamination
A separation of plies or layers of wood, often as a result of the breakdown of adhesives.  

Density
The weight of a substance per unit volume; for example, 23 lbs. per cubic foot.  

Dew Point
The temperature at which condensation occurs.  

Diagonal Rail
A diagonal rail of a crossbuck or sawbuck of a panel or sash door.  

Dimensional Stability
The ability of a material to stay put or to resist changes in its dimensions due to temperature, moisture or physical stress variations; stability of a material.  

Direct-Set
The window’s glass is secured directly into the window frame without the stiles and rails of a sash (e.g. picture window).  

Divided Lite
A window opening divided into smaller sections by a grid system on the interior or exterior of the glass, between the glass panes, or any combination of these three.    

Door Casing
The trim around an interior or exterior door. Exterior door casings are installed only on the outside of exterior door frames, especially on wood facing wood-frame exterior walls. Interior casing covers the inside edges of the jambs and the rough opening between the door unit and the wall.  

Door Frame
The assembly of structural members (head, sill, jambs) used to fasten the door system to the structure.  

Door Jamb
The upper horizontal and the two vertical frame members that house the door panel. Jambs may be classified as head or side jambs.  

Door Panel
An assembly comprised of stiles (vertical pieces), and rails (horizontal pieces) inserted into the door frame.  

Door Skin
A face panel (usually two or more plies) of a flush door.  

Door Trim
Moulding applied around door openings on the exterior and interior. 

Double Glazing
Two panes of glass separated by an air space to form insulating glass.  

Double-Hung Window
A window with two sash, upper and lower, that slide vertically past each other.  

Dovetail Joint
A joint formed by inserting a projecting wedge-shaped member into a correspondingly shaped cutout member.  

Dual-Arm Operator
A window-opening mechanism used on casement windows that is composed of two arms; one pulls the sash while the other pushes.  

Dual-Pull Operator
A window-opening mechanism on awning windows that uses a scissor action and has two keepers.  

Dyad Operator
A window-opening mechanism with a single-jointed arm that is commonly used on small casement and French casement windows.