HERTSMI-2 testing for water-damage molds

HERTSMI-2, explained

The five molds, and what each one points to

The five HERTSMI-2 species don’t all need the same conditions to grow. Knowing which ones drove a score helps narrow down what kind of moisture problem a home has.

Mold	Conditions it favors	What an elevated level can suggest
Stachybotrys chartarum	Cellulose materials, like drywall paper and ceiling tile, that stay wet for a long time	A sustained leak or flood that wasn’t dried quickly
Chaetomium globosum	Wet drywall, wood and paper	Long-term water damage, often alongside Stachybotrys
Aspergillus versicolor	Damp building materials and dust	Ongoing dampness, sometimes without an obvious leak
Aspergillus penicillioides	Drier conditions; can grow in dust and on surfaces with high humidity	Chronic high indoor humidity
Wallemia sebi	Drier conditions; tolerates low water availability	Humidity problems, stored items, or damp dust in closets and basements

So a score driven mostly by Stachybotrys and Chaetomium sends us looking for wet walls and past leaks. A score driven by Wallemia and Aspergillus penicillioides points more toward humidity control. The treatment of the building is different in each case, which is why the species detail matters as much as the total.

How the score is built

The lab measures each species in the dust, reported as a concentration such as spore equivalents per milligram of dust. Each concentration falls into a band that carries a set number of points, and the points for all five species are added together. A species that isn’t detected, or is present only at a low level, contributes nothing. Because of that structure, one heavily elevated mold can push a home into a higher range even when the other four are clean.

Reading a borderline result

A borderline score is where most of the hard questions come from. Before deciding anything, we usually look at three things:

• Which species scored. One mold scoring points is a different situation from all five scoring a little.
• Where the dust came from. If one room was sampled on its own, a second sample from another room can show whether the problem is local or house-wide.
• What the inspection found. A wet wall or a failing dehumidifier gives the number an explanation, and a clear repair.

What happens next is your doctor’s call on the health side and ours on the building side. For many families, it’s a targeted fix of the moisture source followed by cleaning and a retest, rather than a full remediation.

Timing: recently cleaned or remodeled homes

Dust tests need dust. A home that was just professionally cleaned, painted or given new flooring may score low simply because the history was wiped away. That’s a real risk when screening a house for sale or a rental that was turned over between tenants. The same applies after remediation: testing right after a deep clean shows how well the cleaning went, and testing again after a period of normal living shows whether the source is truly gone. We’ll help you decide which one your situation needs.

Where HERTSMI-2 fits with other tests

HERTSMI-2 answers one question well: are the molds most tied to water-damaged buildings present in this home’s dust, and how much? It doesn’t locate them, and it doesn’t measure toxins. For a household managing mold illness, it’s often paired with mycotoxin testing and a moisture inspection. If you’re still deciding between dust tests, our side-by-side look at ERMI vs. HERTSMI-2 walks through the trade-offs.

HERTSMI-2 measures molds in a building’s dust. It isn’t a medical test, and the score bands above are published guidance, not medical advice. We don’t diagnose or treat medical conditions. Your doctor sets your target, and with your permission we’ll share every result with them.