Mold Risk Calculator
See your city's mold risk score, local climate data, and average remediation costs — in seconds.
Mold Risk Calculator
See your local climate risk, average remediation costs, and what to watch for — based on real data for your city.
Not listed? Take our quiz — we cover all US ZIP codes.
How is the mold risk score calculated?
The score (0–10) is based on three factors that directly influence mold growth:
- Relative humidity (0–4 points): Mold requires humidity above 60% to thrive. Cities averaging above 75% get the highest score — that's when mold can grow year-round without any water intrusion event.
- Annual rainfall (0–3 points): High rainfall increases the frequency of water intrusion events (leaks, flooding, ground moisture) that create mold conditions even in drier climates.
- Median home age (0–3 points): Older homes were built before modern vapor barriers, moisture-resistant drywall, and improved HVAC systems. A home built in 1950 has significantly more mold vulnerability than one built in 2005.
The score is a risk indicator, not a guarantee. A high-risk city doesn't mean every home has mold — it means conditions favor mold growth and homeowners should be more vigilant.
What humidity level causes mold?
Mold growth accelerates above 60% relative humidity. At 70%+, many surfaces — drywall paper, wood framing, carpet backing — can support mold growth without any water leak. The EPA recommends keeping indoor humidity below 50% to prevent mold.
Does an older home mean more mold risk?
Generally yes, for three reasons. Pre-1980 homes often lack vapor barriers in crawl spaces and exterior walls. Pre-1990 drywall used paper facing that is more susceptible to mold than modern paperless drywall. And aging plumbing and roofing increase the frequency of slow leaks — the #1 hidden cause of mold.