Raised floor

A raised floor (also raised flooring, access floor(ing), or raised-access computer floor) provides an elevated structural floor above a solid substrate (often a concrete slab) to create a hidden void for the passage of mechanical and electrical services. Raised floors are widely used in modern office buildings, and in specialized areas such as command centers, Information technology data centers and computer rooms, where there is a requirement to route mechanical services and cables, wiring, and electrical supply. Such flooring can be installed at varying heights from 2 inches (51 mm) to heights above 4 feet (1.2 m) to suit services that may be accommodated beneath. Additional structural support and lighting are often provided when a floor is raised enough for a person to crawl or even walk beneath.

In the U.S., underfloor air distribution is becoming a more common way to cool a building by using the void below the raised floor as a plenum chamber to distribute conditioned air, which has been done in Europe since the 1970s. In data centers, isolated air-conditioning zones are often associated with raised floors. Perforated tiles are traditionally placed beneath computer systems to direct conditioned air directly to them. In turn, the computing equipment is often designed to draw cooling air from below and exhaust into the room. An air conditioning unit then draws air from the room, cools it, and forces it beneath the raised floor, completing the cycle.

Above describes what has historically been perceived as raised floor and still serves the purpose for which it was originally designed. Decades later, an alternative approach to raised floor evolved to manage underfloor cable distribution for a wider range of applications where underfloor air distribution is not utilized. In 2009 a separate category of raised floor was established by Construction Specifications Institute (CSI) and Construction Specifications Canada (CSC) to separate the similar, but very different, approaches to raised flooring. In this case the term raised floor includes low-profile fixed-height access flooring. Offices, classrooms, conference rooms, retail spaces, museums, studios, and more, have the primary need to quickly and easily accommodate changes of technology and floor plan configurations. Underfloor air distribution is not included in this approach since a plenum chamber is not created. The low-profile fixed-height distinction reflects the system's height ranges from as low as 1.6 to 2.75 inches (41 to 70 mm); and the floor panels are manufactured with integral support (not traditional pedestals and panels). Cabling channels are directly accessible under light-weight cover plates.

The traditional type of floor consists of a gridded metal framework or substructure of adjustable-height supports (called "pedestals") that provide support for removable (liftable) floor panels, which are usually 2 by 2 feet (0.61 m × 0.61 m). The height of the legs/pedestals is dictated by the volume of cables and other services provided beneath, but typically arranged for a clearance of at least 6 inches (150 mm) with typical heights between 24 and 48 inches (610 and 1,220 mm).^{[citation needed]}

The panels are normally made of steel-clad particleboard or a steel panel with a cementitious internal core, although some tiles have hollow cores. Panels may be covered with a variety of flooring finishes to suit the application, such as carpet tiles, high-pressure laminates, marble, stone, and antistatic finishes for use in computer rooms and laboratories. When using a panel with a cement top surface the panels are sometimes left bare and sealed or stained and sealed to create a tile appearance and save the customer money. This bare application is used most often in office area, hallways, lobbies, museums, casinos, etc.

A contemporary low-profile fixed height type of cable management access floor differs from traditional access floor by requiring much less ramping floor space at floor height transitions, and can even be eliminated in new construction with slab depressions. The primary advantages are realized by much lighter weight panels for easier handling. No tools are required to make changes, and organized cable channel pathways are integral to the system. Time and expense is greatly reduced during installation and every time changes are made in the future during the life of the building. Since this type of access floor is not attached to the structure it is considered to be furnishings, fixtures, and equipment (FF&E) that can be a depreciated expense or leased. Since the underfloor cabling is not in a plenum, the expense of plenum rated cable is not required.

Many modern computer and equipment rooms employ an underfloor air distribution to ensure even cooling of the room with minimal wasted energy. Conditioned air is provided under the floor and dispersed upward into the room through regularly spaced diffuser tiles, blowers or through ducts directed into specific equipment. Automatic fire protection shutoffs may be required for underfloor ventilation, and additional suppression systems may be installed in case of underfloor fires.

Many office buildings use access flooring to create more flexible and sustainable spaces. A large corporation can have over 20,000 miles (32,000 km) of cabling in a single facility.