InterNACHI Mold Inspector key terms

A kingdom of organisms that absorb nutrients from organic material and reproduce by spores. In buildings, visible growth usually signals a moisture problem rather than a contamination event that arrived on its own.

A single thread-like filament of a fungus. Hyphae branch and weave together to form the visible colony and extend into porous materials to extract nutrients and water.

The network of branching hyphae that makes up the body of a mold colony. It is often hidden inside drywall paper, wood, or insulation while only the spore-producing surface is visible.

A microscopic reproductive unit released by molds and dispersed by air, water, insects, or human activity. Spores survive dry periods and germinate when moisture and food become available.

An asexual spore produced at the tip of a specialized hypha and released into the air. Conidia of genera such as Aspergillus, Penicillium, and Cladosporium are the structures most often identified on air samples.

The process in which a spore takes up water and begins to grow a hypha. Germination requires adequate moisture, suitable temperature, and a food source; without liquid water or high humidity it stalls.

A measure from 0 to 1 of how much water in a material is available for biological growth, rather than total water content. Most indoor molds grow when Aw exceeds roughly 0.80.

The moisture level a material reaches when it is in balance with the surrounding air. Wood held above about 20 percent moisture content, or drywall above roughly 1 percent, supports mold growth.

A plant-derived carbohydrate that is a primary food source for many indoor molds. Paper facing on drywall, wood framing, ceiling tiles, and cardboard are common cellulose substrates.

The material a mold grows on, supplying nutrients and often moisture. Dust, skin cells, paper, wood, and fabric can all serve, which is why visible growth is not limited to obviously wet surfaces.

A mold able to grow at relatively low water activity, often around 0.70 to 0.80. Species such as Wallemia and some Aspergillus and Penicillium species can colonize materials that feel only slightly damp.

A mold that requires high water activity, often above 0.90, to grow. Stachybotrys and some Fusarium species are examples and typically appear only after sustained wetting or water damage.

A visible cluster of mold growth arising from one or more spores. Colony size, color, and texture help with field judgment but are not reliable for identifying species without laboratory examination.

The uncontrolled entry of liquid water into a building through leaks, gaps, or failures in the envelope. It is the most common cause of persistent mold growth in buildings.

Any origin of water vapor or liquid water in a building, including plumbing leaks, roof failures, condensation, groundwater, and occupant activities. Identifying the source is the first step in any mold response.

The change of water vapor into liquid when air cools below its dew point or contacts a cold surface. It commonly forms on windows, cold water pipes, and ductwork and can wet materials without any leak.

The temperature at which air becomes saturated and water vapor begins to condense. Surfaces colder than the dew point in a given space will collect moisture.

The amount of water vapor in air expressed as a percentage of the maximum the air can hold at that temperature. Sustained indoor RH above roughly 60 percent favors mold growth on cool surfaces.

A part of the building envelope that conducts heat more readily than surrounding assemblies, such as a steel stud or concrete slab edge. Its cold interior surface promotes condensation and hidden mold.

The exterior shell of a building, including walls, roof, windows, doors, and foundation, that separates interior from exterior conditions. Gaps or failures in the envelope allow air and water movement.

A material, usually plastic sheeting or a coated membrane, installed to limit water vapor diffusion through an assembly. Placement matters: an improperly located barrier can trap moisture and cause hidden rot or mold.

Metal or membrane installed at roof edges, wall intersections, and openings to direct water away from the building. Failed flashing is a frequent source of concealed wall and ceiling moisture.

A field instrument that estimates water content in building materials by electrical resistance or capacitance. It is used comparatively to map wet areas and confirm drying, not to give absolute laboratory values.

Use of an infrared camera to show surface temperature differences that may indicate hidden moisture, air leakage, or missing insulation. Findings are suggestive and must be confirmed with a moisture meter.

Insertion of a small camera through a drilled hole or existing opening to view concealed cavities such as wall interiors. It allows confirmation of hidden growth without major demolition.

A characteristic earthy smell produced by microbial volatile organic compounds from active growth. It is a useful screening clue but is subjective and not proof of contamination or of a specific organism.

Growth that can be seen without magnification, often appearing as staining, discoloration, or fuzzy patches. Visible growth alone justifies a response; sampling is usually not needed to confirm its presence.

A written strategy stating why samples are taken, where, how many, and how results will be interpreted. A plan set before sampling reduces bias and prevents over-reliance on numbers.

Systematic error introduced by choosing sample locations, times, or methods that do not represent the building conditions. It can make a clean space appear contaminated or hide an active problem.

Collection of airborne spores and particles, usually with a pump-driven cassette or an impactor. Results reflect only the moment of sampling and vary widely with activity, ventilation, and weather.

An air-sampling cassette that collects particles on a sticky surface for direct microscopic count and identification. It provides total counts and genus-level categories but cannot show whether spores were viable.

Air or surface sampling on culture media that grows organisms so colonies can be counted and identified. It detects only organisms able to grow under the chosen conditions and is slower than direct microscopy.

Laboratory growth of organisms on a nutrient medium to identify them and estimate quantity. Culture results depend on medium, temperature, and incubation time, so they are not directly comparable to spore-trap counts.

Microscopic inspection of tape-lift, swab, or bulk samples to identify mold structures and confirm growth. It shows what is present on the sampled spot but does not measure airborne exposure.

A surface sample made by pressing clear tape onto growth and mounting it on a slide. It preserves structures for identification but captures only a small area and cannot quantify contamination.

A piece of material removed for laboratory analysis of mold growth within or on it. It is useful for confirming hidden growth but is destructive and should be limited to necessary locations.

A sample taken from an unaffected area or from outdoor air for comparison with a suspect location. Without a control, a single elevated count is difficult to interpret.

The process of removing mold growth, correcting the moisture source, and cleaning or removing affected materials. Verification and documentation are part of the job, not an optional extra.

Physical barriers and negative air pressure used to keep dust and spores from spreading to clean areas during remediation. It protects occupants and prevents cross-contamination of the rest of the building.

A condition in which the contained work area is kept at lower pressure than surrounding spaces, so air flows inward. It is maintained with fans and HEPA-filtered exhaust and checked with a manometer or smoke.

A vacuum equipped with a high-efficiency particulate air filter that captures very fine particles, including spores. It is used for cleaning and final cleaning rather than for removing visible growth.

An independent post-remediation assessment confirming that the source was corrected and that visible growth and settled spores were removed. It relies on visual inspection, moisture readings, and, when justified, sampling.

A documented conclusion that a remediated area is ready for reconstruction or reoccupancy. It should state the basis for the decision, such as visual inspection and acceptable moisture levels.

A written plan describing the scope of work, containment, protective measures, removal methods, and verification criteria. It should be tailored to the specific building and moisture problem.

Gases released by actively growing molds that produce musty, earthy odors. They are a sign of active growth but are not used as a quantitative measure of contamination.

A material that absorbs and holds water, such as drywall, carpet, insulation, and ceiling tile. Porous materials with mold growth generally cannot be cleaned effectively and must be removed.