Mold Gases and Very Sensitive People

Spores and other solid particles cannot pass through intact drywall. Gases can. When mold grows inside a wall or ceiling cavity, room air samples and dust tests may show little or nothing while gases seep into the rooms through cracks, outlets and gaps. Air in a house also tends to move upward (the stack effect), so a musty smell upstairs may start in a basement or crawlspace.

A veteran inspector came to believe that mold gases were badly underrated as a cause of symptoms, and that some of the worst reactions she saw, in clients and in herself, seemed to come from gases rather than particles.

Evidence: Mixed or limited evidence.

Current guidance: Health researchers generally see MVOCs as a helpful marker of concealed growth. Whatever the research on single compounds shows, a musty smell in a home means something is growing, and that is reason enough to find it.

• A HEPA air purifier captures particles. It does nothing for gases.
• Gases need a large amount of activated carbon. But mold and bacteria can grow in carbon, so a carbon unit run in a damp basement or other moldy area can become a source itself, blowing spores and gases back out. Where it is damp, pick a purifier that uses little carbon or none, and keep every unit clean and maintained.
• Carbon also fills up over time and can begin releasing what it trapped.

Evidence: Well supported (HEPA is a particle standard and does not capture gases). The caution about carbon in damp areas is Inspector's practice (precautionary).

An N95 or P100 respirator filters particles only. To reduce mold gases, the respirator also needs an organic-vapor cartridge. Anyone with heart or lung problems should check with a doctor before wearing a respirator.

Evidence: Well supported (CDC/NIOSH respirator classes).

One long-time inspector described a two-story dormitory where students had allergy and asthma symptoms. The source was a large, unventilated and very moldy crawlspace beneath the building. Yet air and surface samples in the living areas looked reasonably good. There was no money for a cleanup, so the building's engineer fitted a pair of exhaust fans on one side of the crawlspace and opened a pair of vents on the opposite side. The complaints stopped.

Her reading: if particles were not getting into the rooms, then the fragments and toxins carried on particles were not either. That left gases. The fix worked only because the building stood in the woods. Moldy air should never be blown toward a neighbor's home. She called the result workable rather than ideal.

The lasting answer is to find and remove the growth, because gas production stops when growth stops. While that is under way, or when hidden mold cannot reasonably be reached, bringing in fresh outdoor air dilutes what remains. In one family's case, with test results showing mold gases throughout the house but no clear source, filtered and dehumidified outdoor air was fed into the ductwork so it came out of every vent. That kept the house at slightly higher pressure than outdoors, which pushes stale air out rather than drawing it in from walls and crawlspaces. In cold climates, keeping a house under positive pressure can push warm, moist indoor air into the walls, where it can condense, so plan it with a building professional.

Evidence: Well supported for ventilation as a way to dilute indoor air pollutants (EPA, ASHRAE). Its effect on mold-related symptoms is Inspector's practice (precautionary).

People who react strongly to mold often notice problems before any test does. One inspector had a client who felt dizzy in exactly the spots where hidden growth was later found. A reaction is not proof, but it is worth taking seriously as a clue about where to look.

This page is for education only. It is not medical, legal or engineering advice. The inspector whose work this builds on was an environmental consultant, not a physician. Talk with your doctor about health concerns, and use licensed professionals for electrical work and large mold jobs. Products, prices and labs mentioned reflect the years they were recorded and may have changed.

Source: the field work of environmental inspector May Dooley, MS, MA, CMC

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