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After the Storm: Managing Mold Risks Indoors

After heavy storms, either from rain in spring or summer or heavy snow storms and melting aftermaths, property and building managers face more than just visible water damage. Mold, a persistent and costly indoor air hazard, thrives in damp conditions left behind by flooding, leaks, and power outages. Here’s how weather drives mold spore counts and what facilities can do to protect occupant health in every season.

Storms Drive Mold Spikes

When rain or snow melts rapidly and seeps into buildings, moisture accumulates in carpets, drywall, basements, and HVAC systems. Local spore counts can exceed 6,000 spores per cubic meter after severe storms (for example sited in cities such as Mount Holly, NJ and Philadelphia, PA) and is considered a “very high” level that increases respiratory risks for schools, offices, and healthcare facilities. Humidity and lingering dampness can keep spore levels elevated for weeks, even as the cleanup begins.

Studies show facilities exposed to high mold counts post-storm experience more frequent asthma attacks and respiratory illness. Emergency department visits for asthma can rise by over 15% when fungal spore levels double due to wet weather events. Mold-related medical expenses in the U.S. exceed $18 billion annually, impacting everyone from schools to senior living communities.

Winter Heating: Not a Cure-All

With winter’s arrival, most buildings rely on heating systems to keep occupants comfortable. Proper heating helps reduce the risk of mold by curbing condensation on cold indoor surfaces. It’s best to keep temperatures above 14°C (57°F), ideally near 20°C (68°F). This prevents the damp conditions mold requires to thrive on walls, windows and insulation.

But winter isn’t mold-free! When windows remain closed and ventilation drops, moisture from showers, cooking, or minor leaks can build up. Many buildings are still susceptible to mold growth if humidity levels sneak above 60%. Cold weather brings its own mold hazards—condensation on windows, under-insulated walls, and reduced ventilation can all contribute to moisture buildup indoors. Keeping heat running doesn’t eliminate risk; in fact, warm indoor air meeting cold surfaces often creates hidden problem areas for mold growth.

Tips for Healthier Buildings

  • Act fast after storms: Inspect for visible and hidden moisture; remove damp materials within 48 hours.
  • Monitor indoor air: Regular professional air quality testing helps catch problems before health effects spike.
  • Ventilate: Run bathroom and kitchen exhaust fans, especially in winter; avoid indoor air stagnation and excess humidity.
  • Address leaks quickly: Don’t wait – fix leaks and dry out affected areas to halt mold growth at the source.
  • Keep up with seasonal maintenance: Schedule inspections before and after major weather events; share practical weekly tips with your team to reinforce healthy practices.

Detecting and Measuring Mold: Practical Steps

1. Recognize Signs of Mold

  • Visual clues: Look for discoloration (black, green, or brown spots) on walls, ceilings, around windows, behind baseboards, or under carpets. Even pale marks can hide a larger problem.
  • Odor: Musty, earthy smells—especially in basements, crawl spaces, or after storms—often signal hidden mold.
  • Water damage: Any sign of water stains, bubbling paint, or damp surfaces should prompt a more thorough inspection for mold.

2. Check Hidden Areas

  • Mold often lurks behind walls, inside HVAC systems, under wallpaper, and in attic or crawl spaces – not just on visible surfaces.
  • After leaks or flooding, carefully remove or check behind furniture, cabinetry, and storage boxes in affected areas.

3. Monitor Indoor Humidity

  • Use a hygrometer to measure humidity; readings above 60% raise the risk for mold growth, even when mold isn’t yet visible.
  • Keep humidity between 30–50% for prevention.

4. Track Occupant Symptoms

  • Increased allergies, coughs, or asthma attacks in specific rooms can be a clue—especially when symptoms improve outside the building

If you discover mold covering more than a 10-square-foot area, or if your building accommodates sensitive populations – such as children, the elderly, or those with compromised immune systems – it’s important to engage certified professionals for a thorough assessment and safe, effective remediation.

For more information contact Tim Popp, VP Industrial Hygiene, at timp@ttienv.com

For Further Guidance: The Centers for Disease Control and Prevention (CDC) and U.S. Environmental Protection Agency (EPA) both provide extensive resources on mold prevention, remediation, and health effects tailored for workplaces, schools, homes, and healthcare environments:

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