Mold doesn't need much to get started. Its spores are already floating in almost every home, and they work a lot like seeds: they sit there doing nothing until they land somewhere damp. Add moisture and they germinate, spread and start releasing more spores. In many attics, that happens every winter. Here's what the research says about mold and health, why attic mold shows up in the cold months, and why moisture control is the step health agencies keep coming back to.
Mold spores are like seeds waiting for water
The EPA explains that molds reproduce by tiny spores that "float through outdoor and indoor air," and that mold may begin growing indoors "when mold spores land on surfaces that are wet." The EPA adds that it's impossible to get rid of all mold spores indoors, but "the mold spores will not grow if moisture is not present."
That's the key point. You can't make a house spore-free. You can make it a poor place for spores to germinate.
Why black mold grows in your attic in winter
Winter attic mold usually comes down to condensation, the same physics we covered in Container Rain:
- Cold roof sheathing. In winter, the underside of the roof deck is the coldest surface in the attic.
- Night-sky cooling. On clear nights a roof radiates heat to the sky. The USDA Forest Products Laboratory notes a roof "may be as much as 10°F to 15°F (5°C to 8°C) colder than the ambient air as a result of radiation to the sky."
- Warm, moist air from the house. Air leaking up through ceiling gaps, light fixtures and attic hatches carries moisture from cooking, showers and breathing.
When that moist air hits sheathing that's below its dew point, water forms on the wood. Day after day of damp plywood is exactly what spores need.
What summer heat really does
Many people believe summer heat kills attic mold. It's a fair guess, because the growth often looks like it stops. What usually happens is that hot, dry conditions send mold dormant rather than killing it. CDC scientists told Congress that mold spores are "capable of resisting dry, adverse environmental conditions, and hence capable of surviving a long time" (CDC testimony, 2002). When moisture returns in the fall, growth can start again. Lab research from Finland's VTT institute backs up what many homeowners see in their attics: wood is at risk of mold when relative humidity stays above about 80% for several weeks (Viitanen 1997), and when conditions turn dry, mold goes inactive but "can become active quickly" once moisture comes back (Viitanen 1994). In other words, mold grows in the moist winter and stops growing in the dry summer heat. Moving moist air out of the attic helps keep it below that line year-round.
Even dead mold isn't harmless. The EPA's mold course says "Mold does not have to be alive to cause an allergic reaction. Dead or alive, mold can cause allergic reactions in some people." That's why the EPA says killing mold isn't enough. It has to be removed, and the moisture problem has to be fixed.
What the studies say about mold health issues
Three major reviews link damp, moldy buildings to health effects:
- Institute of Medicine, 2004. The Damp Indoor Spaces and Health review found "sufficient evidence of an association between damp indoor environments and some upper respiratory tract symptoms, coughing, wheezing, and asthma symptoms in sensitized persons."
- World Health Organization, 2009. The WHO guidelines on dampness and mould found that people in damp or mouldy buildings "are at increased risk of respiratory symptoms, respiratory infections and exacerbation of asthma." The WHO also noted that "remediation of dampness can reduce adverse health outcomes."
- CDC. The CDC says mold can cause "a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash," that people with asthma or mold allergies "may have severe reactions," and that people with weakened immune systems or chronic lung disease "may get infections in their lungs from mold."
The EPA adds that mold exposure can irritate the eyes, skin, nose, throat and lungs of both mold-allergic and non-allergic people.
The "toxic black mold" question
Stachybotrys chartarum, the greenish-black mold often called toxic black mold, gets most of the headlines. The science is more careful than the headlines. The CDC says "no test exists that proves an association between Stachybotrys chartarum and particular health symptoms," and that all molds "should be treated the same with respect to potential health risks and removal." In its 2002 testimony, the CDC said links between indoor mold and effects "such as bleeding from the lung, or memory loss, have not yet been scientifically substantiated."
So the respiratory and allergy effects are well established. Claims about memory loss and other severe illness from black mold are still debated.
The lawsuit that put mold in the news
The best-known mold case in the U.S. is Melinda Ballard's suit against Fire Insurance Exchange, part of Farmers Insurance Group, over water and mold damage to her home in Dripping Springs, Texas. In 2001 a Travis County jury awarded her about $32 million. In December 2002 the Texas Third Court of Appeals cut the award to approximately $4 million. It upheld findings of bad faith and a deceptive trade practices violation, threw out the punitive and mental anguish damages, and sent the nearly $9 million in attorneys' fees back to be recalculated.
It's worth being clear about what the case was. It was about how the insurer handled a property claim, not a court ruling that mold caused illness. In the same appeal (Allison v. Fire Insurance Exchange), the court upheld the exclusion of the family's medical causation experts, so the personal injury claims didn't go forward.
The cost of mold in court
The Ballard case set off a wave of mold claims, and the bills were huge. According to the Insurance Council of Texas, mold claims in Texas "grew from $420 million in 2000 to just over $1 billion in 2001. In 2002, mold claims exceeded $2 billion." Nationwide, the Insurance Information Institute reported that "US insurers paid out at least $3 billion in mold-related claims in 2002, more than double the $1.3 billion paid the previous year." It also found the typical homeowners mold claim cost "$15,000 to $30,000 to handle," compared with $3,000 to $4,000 for a claim without mold.
Big buildings weren't spared. Hilton shut the Kalia Tower at its Hilton Hawaiian Village in Honolulu after mold was found in 2002, a problem the company said cost more than $55 million to fix. Hilton later recovered $25 million from the builders it sued, and a judge approved a $1.83 million settlement for guests who stayed in the tower.
After those losses, most insurers began limiting or excluding mold coverage. That means today the cost of an attic mold problem often lands on the homeowner, which is one more reason to stop moisture before mold gets started.
Why moisture control is the answer
Every agency above lands in the same place. The EPA puts it plainly: "The key to mold control is moisture control." The CDC recommends keeping indoor humidity "no higher than 50%" and making sure "the air in your home flows freely." The WHO calls preventing persistent dampness the most important way to avoid health effects.
In the attic, moisture control means:
- Seal ceiling air leaks so moist indoor air stays out of the attic.
- Fix roof and plumbing leaks quickly.
- Vent bathroom, kitchen and dryer exhaust outdoors, never into the attic.
- Keep air moving from low to high. Steady ventilation carries moist air out before it can settle on cold sheathing. Our solar fans are built to assist your soffit and passive vents, not overpower them. Read more in Why Solar Blaster Bets on Balance, Not Brute Force.
Caveats
- Ventilation is one part of moisture control, not a cure-all. In humid climates, outdoor air can carry moisture in, so sealing air leaks matters just as much.
- Our fans help vent moist air. They don't treat, cure or prevent any illness, and they won't remove mold that's already growing.
- If you have symptoms you think are related to mold, see a doctor.
- The EPA says that if mold covers more than about 10 square feet, or there's been a lot of water damage, follow professional guidelines. For attic mold remediation, hire a qualified professional.
As Daniel Rheaume of Solar Blaster puts it, "Our products move air, which is a natural cleanser. Clothesline fresh."
Questions about moisture in your attic or shed? Call us at (480) 747-7097 or email sales@solarblasterfans.com.