The space between a suspended ceiling and the slab above holds ductwork, cable, sprinkler piping, insulation and often return air. Shaft walls built from gypsum panels enclose risers and elevator hoistways. Columns are wrapped with furring and drywall. Every one of these spaces can take on water from a leak above and none of them can be seen from the occupied floor. A thorough moisture inspection opens or probes them deliberately.

Terms you will hear

Plenum
The space above a ceiling or below a raised floor, often used to carry return air back to the HVAC system.
Shaft wall
A fire-rated gypsum wall assembly enclosing a vertical shaft, typically built from one side with special studs and panels.
Moisture meter
A handheld tool, pin or pinless, that estimates the moisture content of a material.
Thermal imaging
A camera that shows surface temperature differences. Evaporating moisture often appears cooler, but readings must be confirmed with a meter.
Dry standard
A reading taken from the same material in an unaffected area, used as the target for drying.
Cavity drying
Directing dry air into wall or ceiling cavities through small openings so they can dry without full removal.

How a careful inspection is done

  1. Start from the source and work outward

    Follow the water's path through each floor, checking the ceiling space, shaft walls and columns near risers and the building perimeter.

  2. Scan, then confirm

    Thermal imaging can quickly point to suspect areas, but only meter readings confirm moisture.

  3. Open what cannot be read

    Lift ceiling tiles, remove access panels, or cut small inspection holes where a cavity cannot be measured from outside.

  4. Map and label

    Record each reading on a floor plan so the same spots are rechecked every day.

  5. Verify before closing

    Cavities are closed and tiles replaced only when readings match the dry standard.

Dry in place or remove?

  • IfCeiling tiles are stained, sagging or wet from dirty waterThenReplace them. Tiles are inexpensive compared with the risk of reusing them.
  • IfInsulation in the plenum or on ductwork is soakedThenUsually removed and replaced, since it dries slowly and can harbor growth.
  • IfShaft wall panels are wet from clean water and still firmThenCavity drying may work; confirm fire-rated assemblies are restored to their original rating if any panels are replaced.
  • IfReadings stay high after several days of dryingThenOpen the cavity to find what is still holding water.

General information for Downtown Denver, not a quote or professional advice. In an emergency, call 911.