25 October 2016


As part of an update of approved abbreviations, my office changed its long-standing ACB (acoustic ceiling board) to ACT (acoustic ceiling tile). Before coming to this office I had always seen ACT, and it took a bit of time to get accustomed to ACB. No one knows where the unusual abbreviation came from, but it is the more logical of the two, as it includes both acoustic ceiling tile and acoustic ceiling panels. Still, it was decided to change from ACB to ACT because it is unusual. I doubt many contractors will ask an architect, "What's ACT?" but it has not been uncommon for contractors, subs, or suppliers to ask us what ACB is.

The change reminded me of a discussion at a CSI technical committee meeting many years ago when we discussed correct terminology for SpecText. It also brought to mind a similar discussion on LinkedIn, which opened with the question, '"Ceiling TILE" or Ceiling "PANEL" -- What's the correct usage?' At the time of the former discussion I thought, as many do, that ceiling tile is 12 inches square, while ceiling panels are 24 by 24, or 24 by 48 inches. That belief lingers on, and appeared in the LinkedIn discussion.

One of the difficult things about specifying ceiling panels or tiles is the inconsistency of manufacturers' literature. It appears that the only commonly used standard is ASTM E1264 - Standard Classification for Acoustical Ceiling Products, which defines both acoustical panel and acoustical tile.
  • 3.2.1 acoustical panel—a form of a prefabricated sound absorbing ceiling element used with exposed suspension systems.
  • 3.2.2 acoustical tile—a form of a prefabricated sound absorbing ceiling element used with concealed or semi-exposed suspension systems, stapling, or adhesive bonding.
Although E1264 defines panels and tiles, those terms often are used interchangeably. Note that neither definition refers to size or shape, the distinction being based entirely on how the acoustic boards are suspended. In fact, dimensions are not referred to in the standard, nor is configuration; the panels or tiles can be any size, and they don’t have to be square.

Even though the meanings of the terms panel and tile are clarified, E1264 is a surprisingly complicated standard. In addition to the two definitions above, it specifies fifteen Types (I through XIV, plus Type XX), some of which have three or four Forms, and thirteen patterns (A through L, plus Z), flame spread classifications, and several edge designs: butt, reveal, kerfed and rabbeted, square, and beveled. Despite the inclusion of so many characteristics, the standard remains vague, using imprecise terms such as "large holes," "small holes," "lightly textured," and "heavily textured."

In practice, the complexity of E1264 is rarely, if ever, invoked. Drawings typically show ceiling panel and tile dimensions, and finish schedules and specifications typically define other characteristics by specifying specific manufacturers and model numbers, so there is no need to understand all the details of E1264.

We use standards to improve consistency and to minimize confusion. While I don't think anyone is going to have a problem with this specific item, applying the same logic to an entire project is bound to cause problems. For example, and this is an all too common problem, the same material may be identified by different terms in the same set of documents. Why can't the design intent be expressed using accepted definitions and standards?

On a related topic, what's a tegular edge? Going back to the CSI committee meeting I mentioned before, we found that it's a term perhaps first used by Armstrong for a specific edge detail. Armstrong defines tegular as "A functional edge detail that allows a suspended ceiling panel to extend below the grid, making the grid less noticeable." I don't believe Certainteed, National Gypsum, or USG use that term, though Rockfon does. And yet, I often see "tegular edge" used as if it applies to all acoustic ceiling manufacturers, probably because it sounds cooler than reveal edge. Those who use the term don't always know what it means; if I say, "Do you mean a reveal edge?" the response is often, "No, tegular."

By the way, tegular is a real word, meaning "pertaining to or resembling a tile." According to A.Word.A.Day (highly recommended!), the etymology of tegular is:
From Latin tegula (tile), from tegere (to cover). Ultimately from the Indo-European root (s)teg- (to cover), which is also the source of thatch, deck, detect, stegosaur, tog, and protege. Earliest documented use: 1828. 
That makes the way it's used a bit odd, as it doesn't describe the panel itself, which resembles a tile. Instead, it is used to describe only the edge, which does not resemble a tile. To say it pertains to a tile means nothing, as all edges of a panel or tile obviously are related to the tile.

The first definition of tile is usually something like "a thin slab of hard material such as baked clay laid in rows to cover walls, floors, and roofs." A couple of ceramic tile reps insist that the stuff they sell is the tile, and that what goes on ceilings is something else, but not tile. Finally, tegular comes from tegula, which, in construction, means roof tile. (See "Imbrex and tegula" in Wikipedia.) Apparently, some ceiling tile looks like roof tile.

Using a defined term is always the way to go, assuming the term is defined in an accepted standard. ASTM E1264 shows a detail of a reveal edge, and most manufacturers use that term. They often modify it with beveled, angled, square, wide, and narrow, but it remains a reveal edge. In this case, ignoring the standard definitions has resulted in a bit of potential confusion, but widespread use of tegular has essentially created a new standard term.

If the suppliers know the specifiers are using terms interchangeably they won't assume that either is used correctly, but if it appears to specifiers that suppliers don't care, well... I guess it all works out.


  1. I'm a "panel" and "tile" guy.
    "ACT" is the common term used by about 95% of contractors and designers.
    The Types, Forms and Patterns seems to be a way to avoid naming manufacturers' products ... rather like the "Shirt, Man's, Fire-Resistant, Cotton" labels on garments I wore 40 years ago for a summer job.

    1. Sounds about right; reference standards describe things in generic terms, and manufacturers call them whatever the marketing department decides will sell. Thanks for stopping by, Joel!

  2. I have been plagued for years by ASTM's tile/panel definitions. Yet "board" does not work for all products either. For example, I am doing work for a company that makes thermoformed ceiling products that are made from thermoplastic just 0.013 inch thick.

    And while we are on the topic, there is no agreed upon definition of "acoustic ceiling". The term probably originated with matted fiber products. But the above mentioned thermoplastic units have great noise reduction characteristics when used in a suspended ceiling. Does that make them an acoustic ceiling tile or panel or board?

  3. Write a proposal for each and send them to ASTM Committee E33. :)