Dropped ceiling
Encyclopedia
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...
and architecture
Architecture
Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...
. The area above the dropped ceiling is called the plenum space, as it is sometimes used for HVAC
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
air return. The plenum space is also very commonly used to conceal piping
Piping
Within industry, piping is a system of pipes used to convey fluids from one location to another. The engineering discipline of piping design studies the efficient transport of fluid....
, wiring, and/or ductwork
Duct (HVAC)
Ducts are used in heating, ventilation, and air conditioning to deliver and remove air. These needed airflows include, for example, supply air, return air, and exhaust air. Ducts also deliver, most commonly as part of the supply air, ventilation air...
.
A typical dropped ceiling consists of a grid-work of metal channels in the shape of an upside-down "T", suspended on wires from the overhead structure. These channels snap together in a regularly spaced pattern – typically a 2×2 or 2×4 foot grid in the US
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, or 600×600 mm grid in Europe (this is the modular size of the grid, the tiles are actually 595mm x 595mm or 595mm x 1195mm). Each cell is filled with lightweight "tiles" http://www.saint-gobaingyproc.in/mineral-fibre-tiles.html or "panels" which simply drop into the grid. Tiles can be selected with a variety of materials, including wood, metal, plastic, or mineral fibres, and can come in almost any color. Light fixture
Light fixture
A light fixture, light fitting, or luminaire is an electrical device used to create artificial light and/or illumination, by use of an electric lamp...
s, HVAC air grille
Grille
A grille or grill is an opening of several slits side by side in a wall or metal sheet or other barrier, usually to let air or water enter and/or leave but keep larger objects including people and animals in or out.-Spelling:In the United States, "grille" is used to differentiate the automotive...
s, and other fixtures are available which can fit the same space as a tile for easy installation. Most tile material is easily cut to allow fixtures in other shapes, such as incandescent lights, speakers, and fire sprinkler
Fire sprinkler
A fire sprinkler system is an active fire protection measure, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected...
heads.
The suspended ceiling was originally developed to conceal the underside of the floor above and to offer acoustic balance and control in a room. The acoustic performance of suspended ceilings has improved dramatically over the years, with enhanced sound absorption
Absorption (acoustics)
Acoustic absorption is that property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to that sound energy that material reflects or conducts. Acoustic absorption is represented by the symbol A in calculations...
and attenuation
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
. This is sometimes achieved by adding insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
known as Sound Attenuation Batts (SABs), more commonly referred to as "sound batts", above the panels to help deaden sounds and keep adjacent rooms quieter.
The dropped ceiling was invented by Donald A. Brown of Westlake, Ohio
Westlake, Ohio
Westlake is a city in Cuyahoga County, Ohio, United States. The population was 32,729 at the 2010 census. It is an affluent suburb of Cleveland, Ohio and is located 12 miles from Cleveland's downtown.-Geography:Westlake is located at...
, who was claimed by some to having cornered the entire market on dropped ceilings. He was killed in a plane crash on January 18, 2010. Brown filed a patent for a "suspended tile ceiling" on September 8, 1958, and was awarded patent No. 2,984,946 for "Accessible Suspended Ceiling Construction" on May 23, 1961.
Concealed grid
This system has some major disadvantages compared to the more common "drop panel" system, most notably the difficulty in removing and reattaching panels from the grid, which in some cases can cause irreparable damage to the panels removed. Finding replacement panels for this type of dropped ceiling is becoming increasingly more difficult as demand for them is slowing, as is production of the parts. Small clips are still available which allow tiles to be inserted into gaps in the ceiling where a tile is missing, they work by being placed on the edge of a concealed tile, then being slid along as the tile is placed to 'lock' it in place.
Safety Issues
The space above the dropped ceiling is often used as a plenum air return for ventilation systems, requiring only enclosed ducts that deliver fresh air into the room below. Return air enters the ceiling space through open grilles across the ceiling.In the event that the dropped ceiling is used as a plenum, low-voltage cables and wiring not installed inside conduit need to use a special low-smoke and low-toxicity wire insulation which will tend to char and stop burning on its own. This helps to protect building occupants so that they are not poisoned with toxic chemicals sucked through the ventilation system in the event of a fire, and helps to prevent fires from spreading inside the hidden plenum space. This special low-smoke cable is typically referred to as plenum cable
Plenum cable
Plenum cable is cable that is laid in the plenum spaces of buildings. The plenum is the space that can facilitate air circulation for heating and air conditioning systems, by providing pathways for either heated/conditioned or return airflows...
or Low Smoke Zero Halogen
Low Smoke Zero Halogen
Low smoke zero halogen or low smoke free of halogen is a material classification typically used for cable jacketing in the wire and cable industry. LSZH cable jacketing is composed of thermoplastic or thermoset compounds that emit limited smoke and no halogen when exposed to high sources of...
(LSZH or LS0H) cable. While networking cable is the most common form of plenum cable, coaxial cable and telephone cable also needs to be plenum-rated for safety.
High-voltage electrical equipment (generally regarded as being over 50 volts) is not permitted to be exposed in the plenum space above a drop ceiling. High voltage wiring must be enclosed in conduit or raceways, and must be physically isolated from low-voltage wiring. High voltage electrical devices similarly must be enclosed in a plenum space, inside a metallic container. Similarly, electrical outlets for domestic powered devices are not permitted inside the plenum space, though outlets can be installed on ceiling tiles inside electrical boxes, with the sockets exposed on the exterior bottom face of the drop ceiling. The purpose of these restrictions is to limit flame spread inside the unseen plenum space, in the event of high voltage equipment or wiring failure. Low voltage cabling is permitted because current flow is typically negligible so the risk of overheating and fire is limited.
In earthquake prone areas (e.g., California) diagonal wire stays are often required by building codes in order to ensure the ceiling grid won't sway laterally during an earthquake, which can lead to partial or total collapse of the ceiling grid on the occupants below during a severe tremor. Compression posts may also added to keep the ceiling from bouncing vertically during an earthquake.
Lighting fixtures and other devices installed in a dropped ceiling are required to be firmly secured to the dropped ceiling framework. In the event of a fire above a dropped ceiling it is often necessary for firemen to have to pull down the ceiling in a hurry to quickly gain access to the conflagration. Loose fixtures merely resting in the framework by force of gravity can become unseated and swing down on their armorflex power cables to hit the firemen below. Binding the fixtures to the framework assures that if the framework must be pulled down the fixture will come down with it and not become a pendulous swinging hazard to the firemen.
Desirability
In commercial and industrial settings, this allows the obscuring of fittings above the ceiling and access at any time. Drop ceilings may also be used in settings where obscuring fittings or the actual ceiling itself is desirable when wanting to hide problems, such as structural damage. Older, white panels combined with fluorescent lighting are common in many offices, and considered utilitarian, if not unpleasant by some people. More expensive, modern dropped ceiling styles are gaining popularity. Manufacturers are creating suspended ceilings that are designed to be independent from the exterior walls and just be hung from the soffit; resulting in an aesthetically pleasing look whilst maintaining their ability to aid acoustics in room or large area.Fire Safety
If fire safetyFire safety
Fire safety refers to precautions that are taken to prevent or reduce the likelihood of a fire that may result in death, injury, or property damage, alert those in a structure to the presence of a fire in the event one occurs, better enable those threatened by a fire to survive, or to reduce the...
is a factor, ceiling tiles made from mineral fibres, or fire-rated wood panels can be used within the construction to meet acceptable standards/ratings. These same tiles can provide the needed additional resistance to meet the "time rating" required for various fire code, city ordinance, commercial, or other similar building construction regulations. Fire ratings for ceiling panels vary based on the materials used and preparation of each panel. In the UK it can be required for the tiles from certain manufacturers to be clipped into the grid with special ceiling clips in order to provide a fire rating; there are special tiles designed for the underside of mezzanine floors however that can give a fire rating without being clipped.
Ease of modification
Another advantage of a dropped ceiling is that the easily-removed ceiling panels offer instant access to the plenum, greatly simplifying repairs or alterations.Wiring and piping installed behind traditional plaster or wallboard ceilings is extremely difficult to modify once the finished ceiling is in place. Wires must either be fished through hollow spaces in the walls behind the finished ceiling, or the ceiling must be demolished in order for wiring or piping changes to be made.
In contrast, the tiles and other parts of a drop ceiling are easily removed to allow access to the area above the grid to do any necessary wiring or plumbing modifications. In the event of remodeling, nearly all components of the grid can be dismantled and reassembled somewhere else.
In business, the drop ceiling is often used in conjunction with hollow steel studs to construct small office spaces out of a much larger cavernous space. Wiring and other services are run through the open ceiling, down through the hollow stud walls, and to outlets in the work areas. If business needs change, the office spaces are easily dismantled and the overall cavernous space reconfigured with a different floorplan.
Disadvantages
Dropped ceilings are frequently used by slumlord
Slumlord
A slumlord is a derogatory term for landlords, generally absentee landlords, who attempt to maximize profit by minimizing spending on property maintenance, often in deteriorating neighborhoods. They may need to charge lower than market rent to tenants...
s to hide structural and cosmetic damage, loose wiring, insect/rodent infestation, avoiding the need to carry out any repairs or maintenance. Additionally, sometimes walls do not extend past the grid to the actual ceiling. This can present a security risk when used in offices or areas where unauthorized entry may be an issue.
As a renovation tool, dropped ceilings are a quick and inexpensive way to repair a ceiling or reduce HVAC costs, however they tend to show their age quickly— they are sometimes discolored by excessive smoking, sag in the center, and are damaged easily. In older buildings that have seen multiple renovations over time, it is not uncommon for a dropped ceiling to have been installed in one renovation and then subsequently removed in another, its installation having been an inexpensive fix to prolong the time between major renovations.