Dew point is the temperature at which air, cooled without changing its moisture content, becomes fully saturated so water vapor begins to condense; any surface at or below the dew point will collect liquid water out of the air.
What is dew point?
Dew point ties air temperature, relative humidity, and surface temperature together. When a surface (a single-pane window, an uninsulated rim joist, a cold supply duct) drops to or below the dew point of the surrounding air, vapor condenses on it as liquid water, with no plumbing leak involved. That condensed water is a moisture source like any other, and if it persists it supports growth above the water activity threshold. ASHRAE 160 uses surface conditions relative to dew point as a core criterion for moisture-control design, because condensation risk is a design problem as much as a maintenance one (ASHRAE 160).
Why it matters to a mold inspection
Dew point is why mold appears on closet walls, behind furniture on exterior walls, and around windows in winter, where there is no leak to find, just cold surfaces meeting humid indoor air. An inspector who only hunts for leaks misses these, and the fix is different: raise the surface temperature (insulation, air sealing) or lower the indoor humidity, not patch a pipe. The EPA's homeowner guidance points directly at condensation as a controllable moisture source (EPA, A Brief Guide to Mold, Moisture and Your Home). See condensation vs leak and thermal imaging in mold inspection.
MoldMind captures temperature and humidity as structured environmental fields, so a condensation-driven finding can be documented against the dew-point conditions that caused it.
Sources
- ASHRAE 160: surface conditions relative to dew point are a core moisture-control design criterion.
- EPA, A Brief Guide to Mold, Moisture and Your Home: condensation is a controllable indoor moisture source.