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Ceiling Glossary

A list of the ceiling terms and their definitions used on this website and in our installation manuals.

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American Society for Testing Materials
A nonprofit organization that establishes standard tests and specifications for construction materials.  Such tests and specifications usually are referred to by the abbreviation ASTM followed by a numerical designation.

Abbreviation for American Society for Testing Materials.

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Building Officials and Code Administrators. Publishes the National Building Code every three years, with yearly supplements. Most commonly referred to in the northeast states.

Backloaded Insulation
Thermal/acoustical insulation that is placed above the ceiling suspension system and laid across the horizontal grid members. The insulation is covered by the acoustical panels or tiles. Also referred to as backloading.

Bevel Edge
An acoustical tile is considered to have a bevel edge when the face of the tile turns up at the edge at approximately 45 degrees for 1/8" to 1/4" around the perimeter of the tile.

HumiGuard® Plus ceilings are treated with BioBlock®, fungicide treatment to inhibit or retard growth of mold or mildew on painted surfaces.

Border Cut
Cut made on both ceiling panel and grid at the perimeter of the installation.

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Ceiling Attenuation Class (CAC)
A measure of a ceiling tile's ability to block sound from traveling room to room. A ceiling tile with a CAC < 25 is considered low performance, while a CAC > 35 is high performance. CAC is important between rooms and between floors and ceilings.

Ceiling Suspension System
A system of metal members, designed to support a suspended ceiling, typically an acoustical ceiling. Also may be designed to accommodate lighting fixtures or air diffusers. 

Several clip designs are available to suit applications such as fire resistance, wind uplift, and impact. Fire resistance-rated designs have exact requirements, including the mandatory use of hold-down clips for acoustical panels or tiles weighing less than 1.0 pound per square foot (4.9 kg/m2). For rooms with air pressure that's significantly different from adjacent spaces, retention clips may be necessary to hold panels in place.

Cross Tee
Tee that is inserted perpendicular into the main runner of a ceiling suspension system to form different module sizes.

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Bending or deviation from a straight line or course. Used here as the standard by which allowable load for suspension system components is measured.

Double Web
References the number of vertical layers of steel on main runners and cross tees. The most common is a double layer that provides greater stability around light fixtures and air diffusers.

Duty Classification
Load carrying capability of grid components in pounds per linear foot (Light: 5 lbs, Intermediate: 12 lbs, Heavy: 16 lbs)

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Fiberglass Panels
Ceilings made with a base of high density fiberglass, typically with a vinyl surface. Fiberglass panels are dimensionally stable, easy to clean, have mold and mildew resistance, and are economical.

Fire Guard Grid
Fire resistance rated grid.

Fire Rated
Refers to the UL fire resistance rating of an assembly.

Fire Resistance
The property of acting as a barrier to fire for a certain amount of time. Acoustical ceiling systems form a membrane to contain fire within a room. Fire-rated assemblies (including ceiling panels, suspension systems, light fixtures, diffusers, and structural components) are given ratings of one, two, three, or four hours as tested per ASTM E 119.

Method of adding depressions into the face of acoustical tiles or panels during manufacture for appearance and acoustical performance.

Flame Spread Rating
A single number measurement of the flame spread across the surface of a material. Defined by ASTM E 84 commonly known as the 25 foot tunnel test, the number is obtained by comparing with red oak flooring.

Horizontal surface on the face of the tee, visible from below the ceiling. The part of the grid to which the color cap is applied. Most grid system flanges are either 15/16" or 9/16".

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A generic term used to describe a sheet or coil of steel coated with zinc applied in an electrogalvanizing or dipping process.

Thickness of the steel used to make a grid member. May be expressed by a number designation (26 GA.) or in thousandths of an inch (0.013).

Structural system of main beams, cross tees, and associated hardware which hangs from the deck above and supports lay-in, concealed, or surface-attached ceiling panels.

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Hanger Wires
Wire used to suspend a grid system from the existing structure and support ceiling tiles or panels.

Hold Down Clip
Mechanical fastener that snaps over the bulb of a grid system to hold ceiling panels in place.

Hook Tee
Cross tee with an end tab that hooks through the rout hole and rests on the vertical web of the main runner.

Hot Dipped Galvanized
Process used to coat steel to offer resistance to corrosion. Cold-rolled steel is dipped into a molten zinc bath, and a heavy coating of zinc is applied to the steel substrate. Zinc coating thickness varies and is designated by a G series, such as G-60 or G-90.

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Organization based in Sacramento, California, that sets seismic standards primarily for the western United States. Publishes the Uniform Building Code.

Intermediate-Duty Systems
These are used primarily for ordinary commercial structures where some ceiling loads, due to light fixtures and air diffusers, are anticipated.

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Main Beam, Main Runner, Main Tee
Load-bearing beams of a suspension system in which the structural members are mechanically locked together. They provide direct support for cross runners and may support light fixtures and air diffusers, as well as the acoustical tile.

Mineral Wool
A man-made, wool-like material of fine inorganic fibers for thermal and acoustical insulation. 

Cross tee end detail that is installed with a hook insertion, in contrast to the XL tee that is installed with a stab insertion.

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Noise Reduction Coefficient (NRC)
A ceiling tile's measure of the absorption of sound that strikes the surface area. Ceilings with an NRC <.50 are considered low performing, while ceilings rated >.50-.60 are considered good performance, and those with >.65 are considered high performance.

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Offset on the end of some cross tees that rests on top of the supporting members flange. Increases stability and moves cut edge of tee out of the visible plane of the ceiling.

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In suspended ceiling construction, the space between the suspended ceiling and the main structure above.

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R Factor
A number measuring a material's resistance to heat flow. R stands for resistance, the inverse of conductivity.

Rotary Stitching
Process by which two vertical layers of steel are stitched or bonded together to form a stronger, singular piece. Armstrong is the only grid manufacturer to employ this technology.

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Process of cutting grooves into the face of acoustical panels to create different decorative visuals and add acoustical benefit.

For applications where cleanliness is a priority, acoustical units may require cleaning beyond normal maintenance procedures. Acoustical panels with special facing materials such as Mylar or vinyl film offer superior scrubbability without compromising panel finish integrity. Metal ceilings may also be used for scrubbable applications. The accepted test procedure is the Gardner Scrubbability Test ASTM D 2486. 

Stab End Detail
Designed to be inserted in main runner rout hole with a forward, over-the-shoulder motion.

Suspension System
A metal grid suspended from hanger rods, consisting of main beams and cross tees, clips, splines, and other hardware which support ceiling panels or tiles.

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A functional edge detail that allows a suspended ceiling panel to extend below the grid, making the grid less noticeable. 

Temperature and Relative Humidity (RH) Resistance
Temperature and humidity affect an acoustical panel or tile's stability. Standard acoustical panels and tiles are designed for installation within the normal temperature range of 60-80 degrees F (15 to 29 degrees C) and maximum 70 percent RH. When the temperature and RH are expected to exceed these ranges, consider the use of acoustical ceilings designed specifically for these applications, like HumiGuard™ ceilings.

Acoustical ceiling board, usually 12" x 12", which is stapled, cemented, or suspended by a concealed grid system.

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UBC 25-2
Uniform Building Code (seismic standard). 

UL Label
An identification for any product authorized by Underwriters Laboratories, Inc. (ULI) to:

  • have a rating based on the performance of tests in similar products
  • be made from materials and by processes the same as those of similar products which have already gone through fire, electrical, and other performance tests
  • be subject to reexamination by ULI.
Underwriters Laboratories, Inc.

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