What Home Inspectors Can and Cannot Do With Mold
Home inspectors aren't certified industrial hygienists. Most aren't qualified to identify specific mold species, assess air quality, or determine the extent of hidden growth. What they can do is identify visible staining that looks consistent with mold or mildew and flag it for specialist evaluation.
When an inspector writes "suspected microbial growth," they're not diagnosing the problem. They're saying: there's something here that warrants a closer look by someone with testing capability. That's exactly what the ASHI Standards of Practice call for. Inspectors refer findings outside their scope to appropriate specialists. This is the right approach, even though it feels unsatisfying when you're the buyer.
The phrase "could be everywhere" in Diane's summary was the inspector's way of noting that mold visible on surfaces often indicates conditions favorable to growth in other areas. It's not a diagnosis. It's a flag.
Getting a Proper Mold Assessment
Diane hired a certified industrial hygienist (CIH) to do a mold assessment. Cost: $425 for an inspection and air quality samples at two locations.
The findings came back five days later. The basement rim joists had a moderate growth of Cladosporium, a common household mold that develops in humid conditions. Air samples showed slightly elevated spore counts in the basement but normal readings on the main floor. No evidence of growth inside walls or in the HVAC system.
This was good news. The scope was limited to the basement perimeter, and it had a clear cause: the crawlspace below an addition had inadequate vapor barrier, allowing moisture to migrate into the rim joist area.
Who to Hire for Testing
For testing, you want a certified industrial hygienist or a company that does assessment only (not remediation). Hiring a remediation company to assess the problem is a conflict of interest, similar to asking a roofer whether your roof needs replacing. The EPA's mold guidance recommends separating assessment from remediation when possible.
Expect to pay $300-600 for a basic assessment with air samples. More complex situations with multiple sample locations or larger homes will run higher.
What Testing Tells You
Air sampling captures spore counts and identifies species. Surface sampling (swab or tape lift) confirms whether staining is actually mold versus dirt, soot, or other discoloration. Most assessments include both. The report should identify species, concentrations, and whether findings indicate an active moisture problem or a historical issue that's no longer active.
Negotiating After a Mold Finding
Diane used the assessment report to negotiate. She asked the sellers for a $4,500 credit to cover remediation ($2,800 estimated) and crawlspace moisture improvements ($1,600 estimated). The sellers countered at $3,200. Diane accepted.
The negotiation worked because she had a real scope of work from a qualified assessor, not just an inspector's flag on a report. Sellers can argue with "suspected mold." They can't easily argue with a certified industrial hygienist's report showing specific species, specific locations, and a remediation estimate from a licensed contractor.
A few things to know about negotiating mold findings:
- The size of the affected area matters more than the species. Small areas (under 10 square feet) of common molds are minor repairs. Larger areas or aggressive species like Stachybotrys (black mold) are different situations.
- The cause of the moisture matters as much as the mold itself. Fix the source or the mold comes back.
- Documented remediation with clearance testing is worth asking for. You want a paper trail that the work was done correctly.
Diane's Outcome
She closed on the house. The credit covered remediation with a little left over. A remediation company cleaned and treated the rim joists in one day. A separate contractor improved the crawlspace vapor barrier under the addition. Clearance testing came back clean.
Eighteen months later, she had no recurrence. The basement stays dry because the moisture source was actually fixed.
Mold findings during inspection aren't automatically deal-killers. What they require is proper assessment before you either negotiate or walk away. Diane almost walked on a house she loved because an inspector's cautious language spooked her. A $425 assessment gave her the actual scope of the problem, and it turned out to be a manageable one.
The lesson I'd take from her experience: when you see "suspected microbial growth" in a report, your first call is to an industrial hygienist, not a remediation company and not your real estate agent. Get the facts. Then decide.