ERMI Mold Testing
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The US Environmental Protection Authority developed ERMI to provide a straightforward, objective, sensitive and standardized way to assess mold and indoor air quality investigations.

The USEPA developed the ERMI as a ranking system based on dust samples collected from homes, the ERMI will help predict the moldiness of homes. The ERMI test involves the analysis of a single sample of dust from a home. The sample is analyzed using mold-specific quantitative polymerase chain reaction (MSQPCR), a highly specific DNA-based method for quantifying mold species.


Relative Moldiness Index

In order to most effectively use this new tool, the ERMI must be compared to a national database. Indices were determined using this method for 1,096 homes across the U.S. as part of the 2006 HUD American Healthy Home Survey. Individual indices, ranked from lowest to highest were used to create a national Relative Moldiness Index (RMI) Scale.

  • How Does ERMI Work?

    The ERMI test involves the analysis of a single sample of dust from a home. The sample is analyzed using mold-specific quantitative polymerase chain reaction (MSQPCR), a highly specific DNA-based method for quantifying mold species. A simple algorithm is used to calculate a ratio of water damage-related species to common indoor molds and the resulting score is called the Environmental Relative Moldiness Index or ERMI. The ERMI value is typically between -10 and 20.

  • How are samples collected for ERMI testing?

    ERMI testing depends on settled dust, which behaves as a mold breeding ground. The ERMI sample is a combined sample of dust, typically taken from the living room and master bedroom. The required dust samples can be obtained by vacuuming about 2 square meters each of the bedroom and living room carpet for five minutes each. The outdoor control is integrated into the ERMI sample.

  • How can we best utilize ERMI Scores?

    During a mold and moisture inspection an ERMI analysis offers data useful to assist in the assessment of the home by a qualified professional. If the ERMI score indicates that there may be water damage in the house, further detailed inspection, including additional testing such as bulk or mold swab testing may reveal a concealed source of water damage and/or mold.

  • Does living in an environment with a high ERMI score cause health issues?

    There are no explicit guidelines for human health with an ERMI score. The symptoms of mold exposure vary from person to person, depending on the sensitivity of each individual and their degree of mold exposure. The ERMI score should be used in combination with individual mold species quantifications and symptoms of home occupants in order to make a decision. The ERMI score is simply a guideline for the determination of mold exposure levels for home occupants.

Drawbacks of using
only ERMI testing alone

It is easy to understand the limitations of the ERMI test by comparing it to the non-viable air sample test used for Indoor Air Quality inspections. Non-viable samplers (airborne spore traps) draw air for a specified period (typically 5 minutes) at a set air flow rate. This generates a consistent volume of air across the sample media. By measuring exactly the same volume of air in each sample, we are able to compare different samples with a high level of success.

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Inability to determine current conditions

Unlike air sampling, the ERMI test uses settled dust as the sample material which doesn’t necessarily tell us about the current conditions. It may be hard to know how much time has passed since the last time the sampled surface was cleaned. Has it been 3 weeks, or maybe 3 months? The difference in time could be significant, which would naturally produce different results. Let’s say a home hasn’t had any mold problem for the last 2 months. However, there was a 3-day period 3 months ago when many mold spores were released while the property owner opened a moldy tent within the home to dry it out. Perhaps the outside air had a high amount of mold spores for a week and the windows were left open. Clearly, the elevated mold spores were not part of the ongoing mold issue. But they’re still going to show up in the ERMI sample.

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Challenges with interpreting test results

Another challenge related to ERMIs is difficulty in interpreting results. One of the main issues is how the formula treats outdoor spores. The formula separates the mold spores that usually grow outdoors from those that are associated with water damage. Unfortunately, this is a difficult distinction to make. Cladosporium, for instance, is one of the most common forms of mold growth found in places with existing indoor water damage. Yet the ERMI formula positions it as an “outdoor mold spore.” Cladosporium is a ubiquitous mold found both indoors and outdoors. Thus, if a home had significant levels of Cladosporium growing indoors, it would simply be subtracted from the data and the house would achieve a clean bill of health.


ERMI testing definitely has its place if used strategically. ERMI testing can be useful in trying to ascertain the long-term history of a house and an overall sense of the quantity of settled mold spores in the home. ERMI testing is a viable option for defining mold built up by offering comparable information to a baseline from which to start or support a more thorough investigation.

CALL US TODAY to schedule a mold inspection for your home or office in Raleigh, North Carolina. There is never a wrong time to test your property for mold, and it can save you thousands in the future.

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