Assessing Mold in Buildings

Assessment Methodology

People affected by mold need both a physician experienced in treating mold-related illness and a mold-free environment in which to recover.

Indoor mold may be allergenic, infectious, or toxic. The CDC, U.S. EPA, Canada’s CHHC, and the U.S. Institute of Medicine agree that indoor fungal growth and dampness are unacceptable. Health effects depend on immune status, fungal type and concentration, and exposure duration.

Mycotoxins are biologically active substances produced by fungi that may harm people and animals. They are carried in fungal particles, including spores and mycelia, rather than gases or VOCs, and may remain after the fungi die. Exposure may cause respiratory irritation, fatigue, skin problems, memory or joint issues, asthma, cancer, or death.

Because fungi occur naturally outdoors and outdoor air enters buildings, eliminating all indoor fungi and spores is impossible. Infants and older adults may be more vulnerable because their immune systems are underdeveloped or weakened.

Some molds are allergenic, pathogenic, or toxic and can pose serious health risks. Buildings should be kept free of conditions that promote mold growth and contamination.

The EPA generally considers mold testing unnecessary because no federal limits exist and visible or odorous mold should be removed without sampling. Its guidance prioritizes moisture control and professional sampling only when needed, such as confirming thorough remediation.

Assessing a home for mold should never begin with mold testing. Knowing the type and concentration of mold in a home is useful, but identifying the conditions that caused or supported its growth is more important. Unless the underlying cause is corrected, mold will return after removal.

The assessment should begin not with mold testing, but with an evaluation of the HVAC system to determine proper sizing and identify air leaks that create dewpoint to support mold growth. Construction methods should be evaluated for conditions that may promote mold growth. It should determine whether those conditions are present or could develop without an unusual water event. The process includes a detailed visual inspection for water stains or damage on ceilings, ceiling tiles, paint, cabinets, window frames and sills, walls, base trim, flooring, wood trim, and floor coverings. Air registers, duct interiors, the air-handler cabinet, and the cooling coil should also be inspected. Moisture readings are taken from materials in areas susceptible to excess moisture, including concrete floors and walls. Indoor humidity is also measured, although the result reflects only a single point in time.

Building materials with current or past excess moisture indicate that mold growth is active or has occurred. The same applies when construction traps water near the foundation or floor slab, allowing moisture to enter the building.

When these conditions exist, mold growth should be considered current, past, or likely. Mold testing captures only a moment in time and does not provide a complete picture of a building’s air quality. Normal activity can cause contaminants to become airborne intermittently or settle on surfaces, so laboratory samples may not detect them. Mold testing should therefore not be the sole basis for evaluating a home or building.

Temperature, nutrients, and time cannot be readily controlled to prevent microbial growth, but moisture can. Because moisture is the key factor, controlling it is the primary strategy for limiting and preventing mold. Once water enters a building, fungi may germinate, grow, and produce spores within 24 hours.

Healthy Air USA, LLC Clearance Criteria

Fungal Sample Analysis

There are currently no guidelines or regulations to indicate “safe” or normal levels of indoor mold. Therefore, there are no numeric standards. Generally speaking, the overall concentration should be similar to or lower indoors than outdoors. Keep in mind that bioaerosol levels change throughout the day, week, or season, and are also affected by the type and level of activity in the structure.

Air Quality Sciences, Technical Bulletins

We typically expect indoor counts to be 30% to 80% of the outdoor spore counts, with the same general distribution of spore types present. The presence or absence of a few genera in smaller numbers should not be considered abnormal.

Environmental Microbiology Laboratory, Inc.

The following molds should be absent from the fungal test sample:

The following molds are indicators of chronic leaks, spills, or floods:

The following mixtures of molds are indicators of moisture conditions:

A total evaluation of the job should meet the following criteria

Summary

In summary, effective mold management centers on identifying and correcting moisture problems rather than relying primarily on short-term air sampling. The guidance combines building inspection methods, fungal interpretation principles, and post-remediation clearance criteria.

• Prioritize moisture and building conditions: Assessment should begin with HVAC evaluation, construction review, visual inspection for water damage, moisture readings, and humidity measurements. Since fungi can germinate, grow, and produce spores within 24 hours after water enters a building, moisture control is presented as the primary prevention strategy.
• Interpret test results cautiously: No regulatory or numerical standard defines safe indoor mold levels. Indoor concentrations should generally be at or below outdoor levels; typical indoor counts range from 30% to 80% of outdoor counts. Because sampling reflects only a single point in time, it should not be the sole basis for evaluating a building.
• Apply clearance criteria: Post-remediation areas should be clean, free of visible mold, dust, debris, contaminated or water-damaged items, and excess moisture. Building materials should reach equilibrium moisture content, indoor water and high relative humidity sources should be eliminated, and individual spore types should not exceed 150 spores per cubic meter.