Door

The purpose of an opening is:

• for people, animals and objects to pass; some doors are for emergencies only (emergency exit[?])
• for air to pass (ventilation[?])
• for seeing and hearing what happens on the other side (however, some doors are partly or fully made of glass)

The purpose of a closure is:

• for preventing air to pass: reducing air drafts and creating an enclosed space that can be heated or cooled more effectively. The use of doors is essential in colder climes where heating would be very difficult without them, and similarly in climates where air conditioning is used.
• for not seeing or hearing what happens on the other side: privacy, avoiding noise
• for preventing falling out (in vehicles)
• regulation of access. Combined with various types of locks, doors become important safety measures.
• for esthetics (e.g. cupboard doors preventing the sight of the contents).
• for helping prevent fire to spread.

A door is usually fastened in a doorway, that is a frame constructed around the edges of a hole in a wall or other containing structure. The two vertical members of the frame are called jambs.

Types of door Many kinds of doors have specific names, depending on their purpose. The most common variety of door consists of a single rigid panel that fills the doorway, hinged along one side so that it can fold away from the doorway in one direction but not in the other. Many variations on this basic design are possible, such as "double" doors that have two adjacent independent panels hinged on each side of the doorway.

A trapdoor is a door that is oriented horizontally in a floor or ceiling[?], often accessed via a ladder.

A stable door is divided in half horizontally. The top half can be opened to allow the horse to be fed, while the bottom half can be closed to keep the animal inside.

A swing door has special hinges that allow it to open either outwards or inwards, and is usually sprung to keep it closed. Saloon doors are a pair of lightweight swing doors often found in public bars.

An up-and-over door is often used in garages. Instead of hinges it has a mechanism, often counterbalanced or sprung, that allows it to be lifted so that it rests horizontally above the opening.

A barn door is a very large sliding door that covers the entire side of a barn.

Door construction Traditional doors are constructed from vertical planks of wood held together by horizontal beams called ledges (hence ledged door). Often they are strengthened by diagonal beams, running upwards from the hinges, called braces (hence braced and ledged and braced doors).

Recently (c. 20th century) hollow doors have been used, consisting of a thin wooden frame covered by hardboard[?] or plywood. Many houses now have external doors that are aluminium-framed with a polyvinyl chloride exterior.