Photograph of Craig Balchunas inspedcting for mold . Mold Investigation Tips for Home Inspectors

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How should home inspectors handle inspections for mold contamination in buildings? How would a home inspector recognize a mold problem? Are there health risks and other special environmental risks and concerns for home inspectors entering moldy areas? This document answers these and similar questions. This presentation and paper provide advice to building inspectors intending to inspect or test for toxic or problematic mold indoors, addressing inspection methods, how to find mold, where to look, what is likely to be important or not, and what inspection methods and mold test methods are valid or invalid.

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Basic Facts About Basement Water Entry and Mold
Daniel Friedman is a licensed and certified home inspector, areobiologist, forensic microscopist, and sick building investigator who has worked in these fields since 1978. - Presentation Updated 4/13/06; original presentation 10 Jan 01 at the World Inspection Network Conference, Phoenix AZ, and for 6 December 01 for the NY Metro ASHI News - Metropolitan New York chapter of ASHI, the American Society of Home Inspectors. The page top photograph shows Craig Balchunas, a New York home inspector (now retired), examining a building for mold.

From our environmental investigation and lab work on "sick buildings" I've learned some things about inspecting and testing for mold that have helped our general building inspection skills and which suggest some warnings to home inspectors.

Most inspectors get pretty good at spotting the history of water entry in a building. But I've inspected houses that had severe mold with no evidence of leaks. In one house, nothing suggested that there had been 20" of water on the floor. History provided by the owner told a different story. A burst-pipe put 20"of water in the basement nearly 20 years ago. They found the leak, fixed it, and had the basement pumped and "dried" in hours. Armed by hindsight one could spot very faint flood lines on paneling.

Flooding wasn't recurrent and there was no visible damage. Or was there? The owner pulled the paneling away from the drywall. Stachybotrys mold was so thick that it fell out in clumps onto the floor. People in the house had been sick for more than a decade, quite possibly due at least in part to this mold. You can see a photo of the owner pulling off paneling at and our lab photo of this mold at The mold fell right in our face! Was I wearing a respirator? Nope. I was sick with a lung infection for two weeks. Had I been a baby or elderly it could have been a more serious illness.

A Building Inspector's Guide Mold Health Risks

  • Don't disturb mold. Bystanders and occupants have sued careless inspectors who cutopenings or otherwise produced a burst of mold activity in a building. Risks include contributing to illness of building occupants and contamination of building areas if substantial amounts of toxic mold are present and proper containment methods are not used. This does not mean that invasive inspection techniques are prohibited--but methods of inspection need to be chosen based on the situation.
  • If you are in a seriously moldy area, wear a HEPA respirator. Repeated exposure toallergens can cause you to become sensitized even if you have not had problems in the past.
  • If appropriate, keep spectators calm by explaining that you wear the mask because you're entering buildings every day. But keep their noses out of themold too. People who are at particular risk can get sick from a single exposure. (Examples: elderly, babies, people with compromised immune system.)
  • Other risks may be present, related to the same conditions which caused mold growth: Sewer backups - bacterial hazards; wet areas, damaged electrical orother mechanical components, even shock hazards.

An Owner's Guide to Inspecting Homes and Other Buildings for Mold

Any experienced home inspector can identify conditions that riskwater entry or high moisture levels in a house. These conditions promote thegrowth of mold spores. Mold is a natural organism and it's virtually everywhere. The goal of "zero" mold spores makes no sense. But if conditions promote mold growth problems are more likely.

  • Just because you don't see water stains, don't assume there was never a flood or a leak.
  • If a building has had flooding, plumbing leaks, roof leaks, A/C condensate leaks, hidden mold may be at serious levels.
  • Check HVAC equipment and duct work for presence of mold or other allergens. Pay close attention to duct work downstream from air filters and blowers; check blower compartments and duct work for contamination (including dead mice), and check other areas where condensate may have accumulated in duct lines, supporting mold growth. Clean ducts in one area don't assure clean ducts everywhere; a "clean" air test does *not* guarantee no ductcontamination either as variations in temperature, moisture, and mechanical disturbance can suddenly release mold spores into the building air.
  • Just because you don't see mold, don't assume a severe mold infection can't be present (behind walls, under carpets, under insulation, in HVAC equipment.) I've found serious toxic mold colonies in walls which showed no external moisture stains nor external mold growth - the clue was other evidence of a history of leaks into the subfloor, confirmed by an impaction air sampler result.
  • Mold may be present at problem-levels in house air depending on variations in humidity, temperature, season, air movement, and physical activity. Not finding it at a given moment is not an excuse for visual and in some cases invasive inspecting.
  • A home inspection is not an environmental check for unhealthy mold or other bioaerosols orallergens. But if you see moldy conditions, warn your client.
  • Do not assert that a specific illness or complaint is caused by mold. The fourtests (proposed by Burge, Harvard School of Public Health) are stringent beyond your means as an inspector. Mold at high levels may cause and almost certainly aggravates or contributes to a wide variety of complaints.

A Building Owner's Guide to Valid Field and Lab Procedures for Mold

While anyone with proper training, a good eye for detail, and a little building science education should be able to recognize the presence of "mold," it takes a trained expert to identify even the most common of the mold. I've attended a number of classes, schools, workshops to learn field and lab procedures for years and still I can by no means identify all of these species. Nor can any of the other more expert sources with whom I consult.

About 80,000 mold species have been identified and named. About 1,500,000 additional species are not yet identified. Luckily not all 1.5 million species grow in buildings. I estimate that there are about 200 most-common molds that are able to grow in indoor conditions.

  • Some mold test kits are unreliable: Field test kits (petri dish left in house) are being sold by the same folks who hopped on the other Environmental Scare Bandwagons, as well as by some other labs. Finding mold this way might mean something, especially athigh counts.
  • Air testing can give a false "clean house" indication: But air tests, especially passive air tests, for mold are not reliable, and reliance on air sampling for mold is rejected by experts. You might get a false positive (says mold is present at problem levels when it's not) but youwill definitely risk false negatives (says mold is not present at problem levels when it is). Illnesses result from breathing mold spores butalso complaints are associated with ketones given off by mold colonies evenwhen no spores are detected.
  • Swab tests and other tests which rely on culturing are also not reliable as an overall characterization of what bioaerosols are present in a property. Deadspores may still be toxic; non-viable biological materials such as mouse dander won't grow in culture but may be a problem for house occupants as may be bacteria, pollen, animal hair, mite fecal pellets, cockroach fecal pellets, etc. What grows on a culture is what likes to growon that individual media, not necessarily what's the most serious problem in the house.
  • There is a place for each of these test tools, but the fundamental and first method for inspection must include a visual inspection of the property to identify likely problem areas, combined with bulk or surface sampling of visible colonies or other potential contaminants.
  • Remember to keep alert for other more immediate hazards: I found a wet moldy basement which had as a root cause a blocked gas-fired-appliance chimney which risked killing everyone in the building with carbon monoxide - a moreserious risk than mold in that instance.

How Much Mold is a Problem?

  • If you see more than 30 sq.ft. of contiguous mold or mold-contaminated surface present in a building, the mold contamination should be cleaned up by a professional (read "expensive")
  • maller amounts or areas of mold contaminated surfaces can be remedied by a homeowner or cleanup contractor.
  • Some occupants who are sensitized may respond to very low levels of mold spores (orother allergens). I've conducted tests which proved that a client who was hypersensitive to airborne allergens responded to airborne mold at levels far below commonly accepted levels of indication of mold contamination. So don't assume that everyone will be equally happy with moldy walls. A general rule of thumb is that if mold is present indoors at significantly higher levels than outside, it's a problem.

What To Do About Mold: a Concise Summary of Critical Steps

  • Mold Action Plan: What to Do About Mold in Buildings a simple step by step procedure for building owners and occupants as well as links to the New York mold remediation guidelines and to other mold cleanup standards are at Mold Action Plan - at
  • Small surfaces of mold can be cleaned with a dilute bleach solution (watch your eyes!)
  • Not all mold needs to be tested: For many situations, expert field and lab analysis are not appropriate. Clean up the mold, fix the conditions that caused it, and clean your gutters.
  • For larger areas, removal of moldy material and disinfect ion of surfaces is required.
  • People at extra health risk should be out of the building during cleanup. (Elderly, infant, allergic, asthmatic, immune-impaired, etc.)
  • People who have health complaints should first see their doctor, not their home inspector.
  • Where a health complaint exists (respiratory, neurological, immune system) which makes people suspect the house ("I get better when I leave.") andwhere no obvious bioaerosol or allergen or mold is present, an expert might be needed to investigate.
  • Whoever is doing mold cleanup needs to be alert for the discovery, as demolition progresses, of more serious amounts or types of mold. If necessary, work needs to stop for further testing and possibly for setup of containment measures.


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