Doors are essential components in any building structure, not only serving as points of access and exit but also contributing to security, privacy, ventilation, and aesthetics. In building services and maintenance, doors are classified based on various factors, and one of the primary classifications is based on their working operations. This classification is crucial because the selection of a door type affects the usability, maintenance requirements, and overall building performance. On the basis of working operations, doors are broadly classified into the following types: 1. Swing Doors Swing doors are the most commonly used type of doors. They rotate on hinges fixed to the side of the door frame. These doors can be single or double shuttered and generally swing in one direction—either inward or outward. In some cases, especially in commercial spaces, double-action hinges are used to allow the door to swing in both directions. Swing doors require clear floor space for the arc of movement, which must be considered during space planning. Maintenance includes lubrication of hinges, tightening of screws, and regular alignment checks. Swing doors are suitable for rooms, bathrooms, and public buildings. 2. Sliding Doors Sliding doors operate by sliding horizontally along tracks. They do not swing open, hence saving space. These doors may consist of one or more panels that slide over each other or into a pocket in the wall. Sliding doors are often used in areas where space is limited, such as balconies, partitions, wardrobes, and some commercial entrances. Sliding mechanisms include rollers and tracks, which need regular cleaning and occasional lubrication. Proper alignment of tracks is crucial for smooth operation. Sliding doors may also be automated in large facilities or commercial buildings. 3. Folding Doors Folding doors consist of several panels hinged together, which fold upon each other when opened. These doors are suitable for wide openings and where space saving is essential. Bi-fold and accordion doors are common examples. They are used in closets, conference rooms, and industrial storage areas. Each panel is connected with hinges, and the door slides along a track. Maintenance involves regular checking of the hinges, tracks, and rollers. These doors can also be acoustically treated for sound insulation in meeting rooms. 4. Revolving Doors Revolving doors consist of three or four leaves (panels) that rotate around a central vertical axis within a cylindrical enclosure. These doors allow multiple people to enter or exit simultaneously while minimizing air infiltration, which helps maintain indoor climate. Revolving doors are typically installed in commercial buildings, hotels, and airports. Maintenance involves ensuring the central axis is well-lubricated, checking the alignment of the panels, and maintaining the drive mechanism in case of automated revolving doors. Safety features must also be periodically tested. 5. Swinging (Double-Action) Doors These doors swing in both