Ceiling Related Terminology

Archive of Older Topics Archive - Specifications Discussions #6
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  1. What term means the space above a suspended ceiling and below the structural deck above the ceiling?
    – If it is used for air distribution, it is a “plenum”.
    – Is “ceiling cavity” clear enough? “Above-ceiling cavity” “Cavity between suspended ceiling and structural deck above ceiling”?
    – Does “attic” work if the structure above is a roof? If so, what is the word if the structure above is a floor or mezzanine?

  2. What is the best term to describe what one sees overhead when the structure, pipes, ducts, and other services are not concealed above a suspended ceiling?

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  1. interstitial space
  2. exposed structure
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I can’t think of a situation where “ceiling cavity” wouldn’t be clear. If a more detailed description is necessary “cavity between ceiling and structural deck” would seem sufficient.

An attic (at least by ICC definition) is unoccupied space between ceiling framing and roof rafters, which to me means attic would not be an accurate term for the space between a suspended ceiling and roof deck.

The 2nd question may vary for different situations. I typically refer to “overhead structure” and “exposed underside of deck” when specifying painting applications; and usually distinguish between pipes, ducts, and other services in occupied spaces and those in mechanical spaces to indicate field painting requirements.

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I concur with Jeffrey–“ceiling cavity” appears to be sufficiently descriptive of the condition.

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  1. I use “interstitial space” when discussing it in the office, but I don’t think I have ever used that term with a client or on drawings.

  2. “Exposed Structure” or “Open to Structure” I like open to structure because it seams a bit more flexible when you also have spray fireproofing. Technically wouldn’t be exposed, but that’s admittedly splitting hairs.

PS. Seems like Wikipedia likes interstitial space.

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I’ve always thought of interstitial space as an intermediate floor for mechanical & electrical equipment, most often in hospitals, laboratories, or factories.

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The 2019 version of ASTM E1264 - Classification of Acoustic Ceiling Products, adds definition:

“plenum - space between the top (backside) of the finished ceiling and the underside of the floor deck or roof deck above.”

They leave other important terms undefined. For example, Types VIII and IX ceilings are “scrubbable,” but that term is not defined.

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Harris’s Dictionary of Architecture and Construction defines “plenum” as the space above a suspended ceiling, whether or not used as part of the HVAC system. (Technically, if part of the HVAC system, it is a “plenum chamber.”)