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Mold Inspection and Detection: How to Find What's Hiding in Your Home

February 25, 2026

A standard mold inspection takes 2-4 hours, costs $670 on average, and often relies on spore trap air tests that miss 85% of Stachybotrys spores (the species most people are worried about). That's not a flaw in any particular inspector's work. It's a flaw in the default testing method.

Here's the tension: roughly half of U.S. homes have current or past water damage, yet the most common test can't reliably detect the mold that water damage produces. The inspection finds the leak. The test is supposed to tell you how bad it is. But if the test can't see what matters, you're making decisions on incomplete data. Incomplete data in this situation can mean either unnecessary panic or dangerous false confidence.

What follows covers that gap: which testing methods produce reliable, species-specific information, how to read a HERTSMI-2 score, and when you need a professional versus when a $199 at-home dust test gives you a better starting point.

Table of Contents

Start Here: Do You Need a Mold Inspection?

Not everyone needs a full professional inspection. But there are three signals that mean you shouldn't ignore the question.

Signal 1: You smell something musty, but can't find the source.

Your nose is actually your most reliable tool. That musty, earthy smell comes from compounds like geosmin, produced by actively growing mold and bacteria. A truly clean home should smell neutral, like fresh air outside. If you notice a damp or "off" smell, especially in closets, basements, or near HVAC vents, something is actively growing.

Signal 2: You see visible water damage or mold growth.

Water stains on ceilings, bubbling paint, warped baseboards. These are signs of moisture intrusion. And mold can begin growing within 24-48 hours of water getting where it shouldn't. Even if you've "fixed" a leak, the damage may already be done behind the wall.

Signal 3: You feel noticeably better when you leave your home.

This one catches people off guard. But it's a strong signal worth paying attention to.

One person's experience illustrates a pattern many recognize:

"I went to South America for two months and my symptoms dramatically improved... I came back home and my health got instantly trashed." -- Reddit user

If any of these apply, the next step is testing your environment, not guessing. You can start with MoldCo's free Signs Quiz to see if your symptoms line up, or jump straight to testing.

What Is a Mold Inspection (and Why It Matters)

People often use "mold inspection" and "mold testing" interchangeably. They're actually two different things, and understanding the distinction matters.

Mold inspection is a visual and instrumental examination. An inspector walks through your home looking for water damage, moisture problems, and visible mold. They use tools like moisture meters and thermal imaging cameras to find hidden leaks and damp spots behind walls.

Mold testing is sample collection and lab analysis. Samples (dust, air, or surface) are sent to a lab to identify which species are present and at what concentrations.

Put simply: an inspection finds the water source. Testing quantifies the contamination.

Both matter. But which you need first depends on your situation. If you suspect hidden mold but can't see anything, testing can confirm whether water-damage molds are present even without a visual finding. If you already see mold or water damage, an inspection helps define the scope of the problem.

Here's the key context: roughly 50% of U.S. homes have current or past water damage, and many of those homes have mold growth that nobody can see. A thorough inspection typically takes 2-4 hours for an average home.

Where Mold Hides: Common Hotspots in Your Home

Mold doesn't always announce itself. The most concerning contamination is often the kind you can't see.

Kitchens: Under the sink (slow drips), behind the refrigerator (condensation line), inside pantry walls.

Bathrooms: Shower grout and caulking, under the vanity, around the toilet base, and anywhere ventilation is poor. Bathrooms without exhaust fans are especially vulnerable.

Laundry rooms: Behind washing machines (hose connections), dryer vents that don't exhaust properly, and floor-level moisture from splashing.

Basements and crawl spaces: These are the most common problem areas because of ground moisture. And here's what many people don't realize: mold from your basement doesn't stay in your basement. Through what's called the "stack effect," contaminated air travels upward through stairwells or pipe chases into the rest of your home.

HVAC systems: Mold forms near evaporator coils, in drip pans, and inside ductwork, especially when filters are overdue for replacement. If you notice a musty smell specifically when your system kicks on, that's a clue worth investigating. For more on this, see Indoor Air Quality and Mold.

Wall cavities and ceilings: This is where mold becomes truly hidden. A slow roof leak or pipe condensation can feed mold growth for months before you see any exterior sign.

Hidden mold behind walls is frustrating because the evidence is often behind the surface, not in front of it:

"For over a year I have smelled a musty, almost urine like smell in a closet of our home... My husband opened up the wall today and found nothing as the obvious source." -- Reddit user

The absence of visible mold doesn't mean the absence of mold.

Mold Testing Methods: What Works and What Doesn't

Not all mold tests are created equal, and the standard method most inspectors use has significant blind spots. Understanding the differences can save you real time, money, and frustration.

Air sampling (spore traps)

A spore trap is a device that pulls a fixed volume of air through a collection cassette over a set period, usually 5-10 minutes. It captures a momentary snapshot of what's floating in the air at that exact time.

The problems are significant. Air tests only capture intact spores, which represent a tiny fraction of what's actually in the air. They can't identify mold below the genus level (they can't tell Aspergillus fumigatus from Aspergillus versicolor, which matters enormously for health). And they miss 85% of Stachybotrys spores because those spores are heavy and rarely stay airborne.

What this means for you: a "clear" air test doesn't necessarily mean your home is safe. Results change based on whether your HVAC was running, the time of day, airflow patterns, and even whether someone recently vacuumed. A single air test is like checking the weather by sticking your hand out the window for 10 seconds.

DNA-based dust testing (HERTSMI-2 and ERMI)

This is fundamentally different. Instead of capturing a momentary air snapshot, dust testing analyzes the DNA of mold species that have accumulated in settled dust over weeks or months. It's a cumulative record rather than a single moment.

The method, called MSQPCR (Mold Specific Quantitative Polymerase Chain Reaction), was developed by Steve Vesper at the EPA in 2007 using data from 1,096 nationally representative U.S. homes. It identifies mold species by their genetic material, so you know exactly which species are present and at what concentrations.

HERTSMI-2 focuses on the 5 mold species most strongly associated with water-damaged buildings: Aspergillus penicillioides, Aspergillus versicolor, Chaetomium globosum, Stachybotrys chartarum, and Wallemia sebi.

ERMI (Environmental Relative Moldiness Index) is a broader test that measures 36 species: 26 associated with water damage and 10 common outdoor molds.

Research has confirmed that all four common dust collection methods provide fungal assessments consistent with each other, and that dust and air provide complementary but different information. Dust captures the cumulative exposure history; air captures what's floating right now.

Hardware store "DIY" kits (settle plates)

These are the kits you find at home improvement stores for $10-$30. They're typically settle plates: petri dishes you leave open to collect whatever falls in. They can tell you mold exists in your home, which is true of virtually every home on Earth. They can't tell you what species, how much, or whether it's a health concern.

In practical terms, they don't provide actionable information for a health-focused investigation.

For anyone investigating potential mold contamination, HERTSMI-2 dust testing is the strongest starting point. It provides species-specific, cumulative data that air sampling often misses. You can do it yourself without scheduling an inspector.

Understanding Your HERTSMI-2 Score

Your HERTSMI-2 score is a single number that quantifies the health risk from the 5 key water-damage mold species in your home's dust.

Here's how to read it, based on research studying 807 consecutive patients:

Score below 11: Generally considered safe. In the study, only 6 of 241 patients who returned to homes with scores below 11 experienced relapse. What this means for you: if your home scores below 11, your environment is unlikely to be the primary driver of mold-related symptoms.

Score 11-15: Borderline. Caution is warranted. Remediation is advised, especially for individuals who are sensitive to mold exposure. A professional inspection can help identify and address the moisture source.

Score above 15: Dangerous. In the study, 436 of 438 patients who returned to homes scoring above 15 experienced relapse. If your score is above 15, remediation is necessary before you can expect improvement in your environment.

A few important nuances. High Chaetomium or Stachybotrys on your report suggests the home has had near-standing water for weeks or months. This isn't a minor leak. And HERTSMI-2 tests 5 species, not all mold. It's focused on the species most associated with health effects in water-damaged buildings.

What about EPA's position on ERMI?

You may see that EPA describes ERMI as "a research tool" not intended for routine public use. This is worth addressing honestly.

ERMI was created by EPA researchers and has been studied in peer-reviewed literature across multiple epidemiological studies. Research has consistently demonstrated that higher ERMI values are linked to asthma development and reduced lung capacity, and that reducing mold exposures through remediation or HEPA filtration improved respiratory health. EPA licenses the ERMI technology to commercial labs.

In practical terms: ERMI and HERTSMI-2 are peer-reviewed tools with published data supporting their use. They aren't perfect (no single test is), but they provide species-specific, quantified data that air sampling can't.

For a deeper breakdown of how to read your report, see MoldCo's ERMI/HERTSMI-2 Interpretation Guide.

Want to know what's in your home's dust? MoldCo's Home Test Kit ($199) ships to all 50 states. Collect a dust sample, mail it back, and get species-specific HERTSMI-2 results in 1-2 weeks. Think of it as a way to rule it in or rule it out. Information gathering, not a commitment.

DIY Testing vs Professional Inspection: Which Do You Need?

This isn't an either-or question. It's a sequencing question. Here's a decision framework:

Path 1: Start with a HERTSMI-2 dust test.

If you don't have visible mold or water damage but want to know whether your home has elevated water-damage molds, a $199 at-home HERTSMI-2 test gives you species-specific baseline data. If the score is low (below 11), you likely have your answer without hiring anyone.

Path 2: If your score is elevated or you have visible water damage, hire a professional.

An elevated HERTSMI-2 score (above 11) tells you what's in the dust. A professional inspector tells you where it's coming from: the leak, the condensation, the failed flashing. You need both pieces to fix the problem.

Path 3: If you need both at once, get both.

Some situations (visible water damage with health concerns, buying a new home, post-remediation verification) warrant running dust testing alongside a professional inspection from the start.

Cost comparison: A professional mold inspection averages $670 (range $303-$1,044 depending on home size). A HERTSMI-2 home test is $199. Starting with the dust test isn't about cutting corners. It's about getting species-specific DNA data that many professional inspectors' air tests don't provide.

Generic test kits and amateur approaches can create false confidence:

"He bought a testing kit off Amazon, so that's what showed only the source as having mold, and was still planning to do the work himself..." -- Reddit user

Professional-grade testing matters because you're making decisions about your health and your home based on the results.

How to Hire a Qualified Mold Inspector

Not all inspectors are equal. Here are the five things that separate a qualified mold inspector from someone who'll take your money and miss the problem.

1. Certifications matter. Look for at least one of these: ACAC (American Council for Accredited Certification), NORMI (National Organization of Remediators and Mold Inspectors), or IICRC (Institute of Inspection Cleaning and Restoration Certification). These aren't just letters. They represent specific training in moisture investigation and mold assessment.

2. Independence is non-negotiable. The company that tests should NOT be the company that remediates. An independent inspector has no financial incentive other than giving you an accurate assessment. If the same company finds the mold and offers to fix it, that's a conflict of interest.

3. They should use the right tools. A qualified inspector uses moisture meters, thermal imaging cameras, and DNA-based dust tests, not just air samples. If an inspector only offers spore trap air testing, they're missing the majority of what matters.

4. Ask about CIRS literacy. If you're investigating mold for health reasons, ask directly: "Are you familiar with the Shoemaker Protocol and HERTSMI-2 testing for chronically ill patients?" If they dismiss these concepts or haven't heard of them, they may not be the right fit for a health-focused investigation. For more on the Shoemaker Protocol, see Decoding the Shoemaker Protocol.

5. They should follow the IICRC S520 Standard for mold assessment, which outlines proper procedures for investigation and sample collection.

Standard home inspections don't cover mold. This is a common and costly misunderstanding:

"Used my life savings to buy a house... passed inspection. After about 4 months... I pulled it off and it was covered in mold." -- Reddit user

Moisture readings are a warning sign that deserves investigation, not dismissal:

"During our inspection our inspector said his moisture detector went off... Well fast forward to yesterday, we decided to rip the wall out and found mold." -- Reddit user

A note for renters: Landlord-hired inspectors may follow the wishes of whoever's paying them. If your landlord arranges an inspection and the results come back clean but you're still symptomatic, consider hiring your own independent inspector. Insist on HERTSMI-2 dust sampling in writing. It provides data that's hard to dismiss.

What Happens During a Mold Inspection

If you've never been through one, here's what to expect during a professional mold inspection:

Step 1: Visual examination. The inspector walks through every room looking for water stains, discoloration, bubbling or peeling paint, warped materials, and visible mold growth. They'll check condensation on windows, especially in corners and behind furniture placed against exterior walls.

Step 2: The smell test. A musty, earthy smell is the most reliable indicator of active microbial growth. Your inspector should note any unusual odors in specific rooms or areas. If your home smells clean and neutral everywhere, that's a positive sign.

Step 3: Moisture measurement. Using a moisture meter, the inspector checks building materials throughout the home. Readings of 15-17% in wood or drywall signal active water problems and elevated mold risk. They'll pay special attention to areas around plumbing, exterior walls, and below-grade spaces.

Step 4: Thermal imaging. An infrared camera reveals temperature differences behind walls and ceilings. A cold spot on an interior wall often means hidden moisture: a leak that hasn't broken through the surface yet. This is one of the most valuable tools in an inspector's kit.

Step 5: Sample collection. For health-focused investigations, the inspector collects dust samples for HERTSMI-2 or ERMI analysis. They may also take targeted air or surface samples from specific areas of concern.

The whole process typically takes 2-4 hours for an average-sized home. What a good inspector checks: kitchens, bathrooms, laundry rooms, basements and crawl spaces, HVAC systems, attics, and any areas with known water history.

How Much Does a Mold Inspection Cost?

Here are specific numbers, because vague "it depends" answers don't help you plan.

Professional mold inspection: The national average is $670, with a typical range of $303-$1,044. Homes under 4,000 square feet usually fall in the $300-$400 range. Larger homes run $700-$1,000 or more. If the inspector also collects and sends lab samples, that can add $250-$500.

MoldCo HERTSMI-2 Home Test Kit: $199, available in all 50 states. You collect the dust sample yourself and mail it back. Results in 1-2 weeks.

The comparison matters: for $199, you get species-specific DNA data on the 5 most important water-damage molds. For $670+, you get a visual and instrumental inspection plus whatever testing the inspector recommends (which may be air sampling that misses the species you need to know about).

Many people find the best value in starting with the $199 dust test to establish baseline data, then hiring a professional only if the results warrant it.

Skipping inspection entirely to save money often costs more in the long run:

"They told us everything was perfect for us and to 'save $300' we should not get a home inspection... Now we've already spent over 40k in repairs." -- Reddit user

The inspection isn't the expensive part. The expensive part is what happens when you don't have the right data.

After the Inspection: Next Steps Based on Your Results

Your results are back. Here's what to do with them.

If your HERTSMI-2 score is below 11

Your home is likely safe from a water-damage mold perspective. If you're still experiencing unexplained symptoms, the next step isn't more environmental testing. It's looking at what's happening in your body. MoldCo's Starter Health Panel ($99) measures three biomarkers (MMP-9, TGF-beta1, MSH) that can indicate whether your body is responding to environmental exposures. For a complete overview of testing options, see Mold Illness Testing.

If your HERTSMI-2 score is 11-15

This is borderline territory. Remediation is advised, particularly if anyone in the home is experiencing symptoms. Hire a professional inspector to find the moisture source. That's the critical first step. Without fixing the water problem, any cleanup is temporary.

If your HERTSMI-2 score is above 15

This is a dangerous environment. Remediation is necessary. Here's the sequence:

  1. Fix the moisture source first. This is the most important step. If the leak, humidity issue, or water intrusion isn't completely resolved, mold will return no matter how well you clean.
  2. Hire a certified remediator who follows the IICRC S520 Standard. They should use proper containment with plastic sheeting and negative air pressure machines. The company that remediates should be different from the company that inspected.
  3. Require third-party clearance testing. After remediation, don't rely on the remediator's own "all clear." Have an independent party verify.
  4. Wait approximately 4 weeks, then retest with a HERTSMI-2 dust test, not air testing. It takes time for dust to accumulate, and dust testing is far more reliable than spore trap clearance tests for confirming remediation was done correctly.
  5. Trust your nose. A successfully remediated space should smell neutral, like the outdoors on a clear day. Any lingering musty or damp smells indicate a remaining problem.

If your symptoms persist even after successful remediation, that's when working with a provider experienced in mold-related illness makes sense. MoldCo Care offers telehealth support from clinicians trained in treating mold toxicity. For a complete treatment roadmap, see the CIRS Treatment Guide.

Guides in This Series

Related guides in MoldCo's mold inspection and detection series:

Coming soon: detailed guides on musty smell investigation, air purifiers for mold, mold growth prevention, and reducing mold exposure strategies.

Key Takeaways

  • A musty smell is the most reliable sign of active mold. Trust your nose. A clean home should smell neutral.
  • DNA-based dust testing (HERTSMI-2) provides species-specific, cumulative data that air sampling often misses.
  • You can start with a $199 at-home HERTSMI-2 test before deciding whether to hire a professional inspector.
  • Any inspector you hire should be independent from the remediation company and hold ACAC, NORMI, or IICRC certification.
  • HERTSMI-2 scores below 11 are generally considered safe. Above 15 signals a dangerous environment requiring remediation.
  • After remediation, wait 4 weeks and retest with dust sampling, not air tests.
  • The first step in any remediation is fixing the moisture source. Without solving the water problem, mold will return.

Glossary

ERMI (Environmental Relative Moldiness Index): A DNA-based scale developed by EPA researchers that quantifies 36 mold species in settled dust: 26 associated with water damage and 10 common outdoor species. Scale ranges from approximately -10 to 20+.

HERTSMI-2 (Health Effects Roster of Type-Specific Formers of Mycotoxins and Inflammagens, Version 2): A focused test that uses weighted concentrations of 5 key water-damage mold species to score the health risk of a building. Scores below 11 are generally safe; 11-15 is borderline; above 15 is dangerous.

MSQPCR (Mold Specific Quantitative Polymerase Chain Reaction): The DNA-based lab method used to identify and quantify specific mold species. It detects both viable and non-viable mold using species-specific genetic analysis.

IEP (Indoor Environmental Professional): A specialist trained in assessing indoor environments for moisture, mold, air quality, and other hazards.

IICRC (Institute of Inspection Cleaning and Restoration Certification): An industry certifying body for cleaning, restoration, and inspection professionals. Their S520 Standard covers mold assessment and remediation.

ACAC (American Council for Accredited Certification): A certification body for indoor environmental professionals including mold inspectors and assessors.

NORMI (National Organization of Remediators and Mold Inspectors): A professional organization providing training and certification for mold inspection and remediation professionals.

Spore trap: An air sampling device that captures airborne particles on a sticky surface over a short collection period. It provides a momentary snapshot of airborne spore counts.

Moisture meter: A handheld tool that measures the moisture content of building materials. Readings of 15-17% or higher in wood or drywall signal active water problems.

Thermal imaging camera: An infrared camera that reveals temperature differences in building surfaces. Cold spots on interior surfaces often indicate hidden moisture.

Frequently Asked Questions

How accurate are DIY mold test kits from hardware stores?

Hardware store kits are typically settle plates or basic spore traps. They can confirm that mold exists in your air, which is true of every home. But they can't identify specific species, quantify contamination levels, or tell you whether the mold is associated with water damage. For a health-focused investigation, HERTSMI-2 provides quantified, species-specific data that generic kits can't match.

My home smells musty but I can't find mold. How do I locate hidden mold?

Start with a HERTSMI-2 dust test to confirm whether water-damage mold species are present. If the score is elevated, hire a certified inspector (look for IICRC, NORMI, or ACAC credentials) who uses moisture meters and thermal imaging to check wall cavities, HVAC systems, and basement or crawl space areas. Dust testing confirms the presence of problematic molds even when there's nothing visible.

Should I move or remediate if I'm reacting to my home?

It depends on your score, your situation, and whether you own or rent. If you're renting, walking away from a deposit is often worth it compared to ongoing health costs. If you own, get a certified inspector to define the remediation scope before deciding. Poor remediation can actually make things worse by disturbing mold without proper containment.

Is ERMI/HERTSMI-2 reliable if EPA says it's just a research tool?

ERMI was created by Steve Vesper at EPA and developed from 1,096 nationally representative U.S. homes. It's been studied in multiple peer-reviewed epidemiological studies that consistently linked higher ERMI values to asthma development and reduced lung capacity. EPA licenses the technology to commercial labs. It's a peer-reviewed, commercially available tool with published supporting data.

How much does a professional mold inspection cost?

The national average is $670 (range $303-$1,044). Homes under 4,000 square feet typically cost $300-$400; larger homes run $700-$1,000+. MoldCo's Home Test Kit provides species-specific HERTSMI-2 data for $199, a lower-risk first step before committing to a full professional inspection.

What mold testing method should I use?

For a health-focused investigation, HERTSMI-2 dust testing is the recommended starting point. It provides cumulative, species-specific data on the 5 mold species most associated with water-damaged buildings. Air sampling (spore traps) only captures a momentary snapshot and misses the majority of harmful fragments. Start with dust testing; add air sampling or professional inspection if your dust test results are elevated.

Can my landlord's inspector be trusted?

Landlord-hired inspectors may be restricted by the party paying them. If the inspector's report says everything is fine but you're still symptomatic, hire your own independent inspector. Insist on HERTSMI-2 dust sampling in writing. It provides species-specific data that's harder to dismiss than a single air test. Document every communication about mold concerns with your landlord.

What should I do if my inspector recommends urine mycotoxin testing?

Approach this with caution. Urine mycotoxin tests have three significant limitations: (1) there are no validated control standards using healthy populations, so it's unclear what "elevated" actually means, (2) the test can't distinguish mycotoxins from food (chocolate, coffee, grains) versus inhaled sources from a building, and (3) no association with any disease state has been established. MoldCo doesn't endorse urine mycotoxin testing as a diagnostic tool. For more detail, see Urine Mycotoxin Test Accuracy.

Related Resources

If you're looking for a place to start, start with data. Order a Home Test Kit ($199) and know what's in your home's dust in 1-2 weeks. Available in all 50 states.

If you already know you have mold exposure, MoldCo Care offers telehealth support from clinicians trained in treating mold toxicity.

Any health-related claims made on this site have not been evaluated by the Food and Drug Administration (FDA). The information provided on this site is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. MoldCo assumes no responsibility or liability for any errors or omissions in the content of the references, nor for any actions taken in reliance thereon.

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Mold Inspection and Detection: How to Find What's Hiding in Your Home