Mold in rentals: What our data from over 10,000 properties reveals (and how to prevent it)

47% of properties in the USA have a mold problem. 

With over a third of these serving as residential or vacation rentals, that means approximately 68 million rental properties are dealing with mold or dampness. As a property owner or manager, it’s up to you to take action and create safe, healthy spaces for tenants and guests.

The good news is that preventing mold doesn’t need to be a nightmare. With the right technology and smart strategies, you can stop mold before it ever becomes a problem.

In this article, we’ll break down the hidden causes of mold, how to spot it early, and proven techniques to keep your properties protected. We're also sharing exclusive insights from over 10,000 properties using Minut’s Indoor Climate feature to see how property managers worldwide are tackling mold risks head-on.

Data-driven property monitoring for safer rentals

Minut is a leading provider of smart property insights designed to help property managers, operators, and vacation rental owners protect their investments and their tenants and guests

Our mission is to create respectful, safe rental communities with real-time insights and data that ensure properties remain compliant and problem-free.

With Minut’s advanced sensors and monitoring technology, property managers and owners gain a 360-degree view into key environmental factors affecting their rentals, including:

• Humidity levels: Identifying conditions that foster mold growth.
• Noise levels: Preventing disturbances and maintaining tenant and guest satisfaction.
• Temperature changes: Ensuring a healthy indoor climate.
• Occupancy tracking: Helping optimize property use and detect unauthorized stays.
• Marijuana and cigarette smoke detection: Minimizing the damage caused by smoking fumes to your property and neighbors.

By integrating smart technology with actionable insights, Minut empowers property owners to address potential risks before they escalate into expensive problems.

‍Insights from over 10,000 properties 

This article is based on data collected from 10,000+ rentals using Minut’s Indoor Climate feature to build a comprehensive analysis of mold risks in rental properties.

‍Minut’s smart sensors track environmental factors contributing to mold growth, particularly humidity and temperature fluctuations. By continuously monitoring conditions inside rental units, Minut can identify high-risk properties and trigger mold risk alerts for property managers and owners. 

The scale of this analysis also allows us to provide a data-driven approach to mold prevention, helping you:

• Predict mold risks before they become expensive.
• Implement proactive maintenance strategies.
• Educate tenants on mold prevention best practices.
• Save thousands in remediation costs and legal liabilities.

In the following sections, we’ll explore what this data tells us about where and when mold risks are highest and how to take smart, preventative action. 

Are property managers doing enough to prevent mold?

Mold may be a hidden risk in rental properties, but its impact has been highly publicized, with untreated mold causing health issues, structural damage, and financial losses. 

While mold risk awareness is growing, Minut’s data shows that many property managers and owners are still not taking proactive steps to mitigate the problem—or if they are taking action, it’s ineffective.

The cost of ignoring mold

Ignoring mold in rental properties can become both a financial and legal issue. If left untreated, mold will cause expensive property damage, impact your tenants and guests, reduce property values, and expose you to potential lawsuits.

The financial impact:

• Remediation costs: Fixing mold damage costs between $1,373 and $3,325 on average, but severe cases can skyrocket into the tens of thousands.
• Property value decline: Homes with a mold history can lose 20-37% of their value, making them harder to sell or rent.
• Health expenses: Mold exposure contributes to respiratory illnesses and infections, with related healthcare costs reaching billions annually.

Legal risks:

• Tenants can take legal action if mold makes a unit uninhabitable, leading to rent reductions, withheld payments, or lease terminations.
• Property managers and owners may face lawsuits for violating the implied warranty of habitability.

The bottom line is that preventing mold is far more than removing black spots on the wall and ceiling. Your remediation efforts could be the difference between a quick fix and thousands of dollars in damages, legal battles, and lost revenue.

Prevalence of mold risks in rental properties

‍Property managers and owners are increasingly recognizing the damage mold can do to their properties.

Minut’s data shows that:

• Between 27% and 38% of rental units have mold risk alerts enabled, indicating that a substantial portion of property owners and managers are actively monitoring mold risks. This growing percentage reflects an increasing industry-wide awareness of mold-related issues.
• However, the actual prevalence of mold risk worsens in winter months. In Q4 2024, 8.94% of all rental units exhibited significant mold risk, a notable rise from 5.6% in September.
• And a big problem, we found was that 78% of the rental properties that received a "significant" mold risk alert did not successfully lower their risk classification to "low risk." This indicates that some of the most high-risk properties are failing to implement effective measures to mitigate mold issues, allowing the problem to persist and potentially worsen.

Why aren’t property managers taking action?

Despite being alerted to mold risks, a huge percentage of property managers and landlords are not taking sufficient steps to address the issue. Several factors could contribute to this inaction:

1. Limited awareness of mold prevention best practices
   • Many property managers may not fully understand the best ways to prevent and control mold growth, such as maintaining proper ventilation, controlling humidity levels, and addressing water leaks immediately.
   • Without a clear understanding of proactive prevention strategies, managers may rely on reactive measures, which are often less effective and more costly in the long run.
2. Underestimating the financial and legal consequences of mold
   • Some property owners may not realize the financial risks associated with mold, including remediation efforts, potential lawsuits from tenants, and reduced property value.
   • Legal consequences can be severe, as tenants affected by mold exposure may pursue legal action for health-related issues, forcing landlords to cover medical expenses, temporary housing costs, or even legal settlements.
3. Lack of resources for proactive maintenance and remediation
   • Smaller property owners or landlords operating with limited budgets may struggle to allocate funds for regular maintenance, professional mold inspections, and necessary repairs.
   • Some landlords may delay remediation efforts to avoid upfront costs, unaware that untreated mold growth can lead to significantly higher expenses down the line.

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When is your property most at risk?

Mold growth is not random—it follows seasonal patterns, with certain times of the year posing higher risks than others. 

Understanding these seasonal fluctuations can help property owners take proactive steps to mitigate mold issues before they become a bigger problem.

Mold thrives in warm, humid conditions, so if you don’t ventilate your home, late summer and early fall could be a high-risk period. High indoor humidity levels, especially those exceeding 60%, can also create an ideal breeding ground for mold spores. 

Additionally, late summer storms and hurricanes often lead to water damage, further accelerating mold growth in vulnerable areas. 

Properties that experience heavy rainfall during these months are particularly at risk, as lingering moisture can seep into walls, ceilings, and foundations.

However, winter presents the biggest mold risks for properties.

While lower humidity levels outdoors may slow mold growth, indoor conditions mean properties are still highly conducive to mold formation. 

Central heating systems often create condensation, especially in poorly ventilated spaces, leading to moisture buildup on windows, walls, and ceilings. As our data shows, the % of properties with a mold alert was at its highest from September to December 2024. 

Homes and buildings sealed tightly to retain warmth often trap moisture, leading to mold issues in bathrooms, basements, and attics. 

Even everyday activities like cooking, showering, and using heating systems can increase indoor humidity levels, contributing to the spread of mold during colder months.

What type of properties are most at risk?

Mold can affect any property, but some locations and building types are particularly vulnerable. Older buildings face higher risks due to outdated ventilation systems and the absence of modern moisture control features. 

Many of these properties were constructed without mold prevention in mind, leading to recurring mold issues. Additionally, poor insulation in these structures can contribute to condensation problems, exacerbating mold concerns.

Properties located in humid climates, such as the southeastern United States, experience persistent mold challenges due to consistently high moisture levels. Long rainy seasons and tropical environments create the perfect conditions for mold to thrive, increasing maintenance demands for property managers and owners. In these areas, regular inspections and humidity control measures are crucial to preventing mold outbreaks.

As mentioned, water is a big factor in mold growth. This means coastal and flood-prone areas are at significant risk. Properties in these regions frequently deal with excess water intrusion, whether from storm surges, hurricanes, or heavy rainfall. Buildings affected by flooding often require ongoing mold prevention and remediation efforts to avoid costly damage and tenant complaints. 

Without proper moisture control, mold can spread rapidly, leading to potential legal and financial liabilities for property owners.

These findings suggest that property managers and owners should take a seasonal approach to mold prevention:

• In summer and fall, increase ventilation, monitor humidity levels, and conduct proactive inspections to prevent mold growth before it starts.
• In winter, Ensure heating systems effectively regulate indoor humidity to prevent condensation buildup and improve airflow in tightly sealed homes.

How to protect your rentals 

Property managers and owners need to adopt proactive maintenance strategies and ensure tenants and guests are educated on how to handle mold to minimize mold risks.

Proactive maintenance in vacation rentals

When you have access to the property between guests, staying on top of mold risks and taking preventative measures is easier. Property managers who use their monitoring insights can implement targeted maintenance strategies, such as:

• Regular HVAC system cleaning to prevent moisture buildup.
• Using dehumidifiers in high-risk properties (e.g., basements, older buildings).
• Roof, plumbing, and insulation inspections to detect leaks before they cause mold growth.
• Applying mold-resistant paint and materials in vulnerable areas.

Keeping your tenants and guests aware

‍In residential rentals, tenant behavior plays a big role in mold prevention.

To help the cause, property managers and owners should provide clear guidelines to tenants on how to reduce moisture buildup and improve ventilation.

‍Key tenant education strategies include:
✔ Encouraging tenants to use bathroom and kitchen exhaust fans.
✔ Providing guidance on proper heating and ventilation to avoid condensation.
✔ Including mold prevention instructions in welcome packets or lease agreements.

‍Lease agreement clauses for mold prevention responsibilities

‍Including mold prevention clauses in lease agreements ensures that both property managers and tenants share responsibility for preventing mold.

For example, important lease provisions could include:

• Tenant responsibility to report leaks and high humidity promptly.
• Landlord's responsibility to address water damage within a set timeframe.
• Requirements for proper ventilation and dehumidifier use.

Proactively setting expectations helps prevent disputes and ensures quick action if mold issues arise.

‍Technology solutions for property managers and owners

Early detection is the key to mold prevention. Minut’s temperature and humidity sensors continuously monitor indoor conditions and provide real-time alerts when humidity levels exceed safe thresholds.Benefits of real-time monitoring:

• Detects high humidity before mold forms.
• Helps property managers intervene early.
• Reduces long-term damage and remediation costs.

Real-time insights for predictive maintenance

‍You can also use your device’s insights and analytics to help predict mold risks before they occur. Instead of responding to tenant complaints after mold appears, property managers and owners can:

• Use historical data to identify high-risk properties.
• Automate preventive maintenance schedules based on real-time conditions.
• Reduce unnecessary inspections by focusing resources on high-risk units.

A data-driven approach to mold prevention means fewer emergencies, lower costs, and a proactive maintenance strategy that protects rental investments.

‍Automated ventilation & HVAC improvements

‍Poor ventilation is a major contributor to mold growth. Upgrading HVAC systems and implementing automated ventilation solutions can drastically reduce mold risks.

• Smart ventilation systems adjust airflow based on real-time humidity levels.
• HVAC upgrades, such as HEPA filters and dehumidifiers, reduce moisture accumulation.
• Automated dehumidifiers maintain ideal indoor humidity levels, preventing condensation and mold growth.

By investing in technology-driven mold prevention, property managers can protect their properties, minimize health risks, and reduce tenant turnover.

Minut in action: How Lodgeur saved up to $1,500 per mold-related incident

Texas-based rental agency Lodgeur, is fully aware of the mold risks that come with renting properties in one of the most humid US states.

To prevent potential mold damage, the team installed Minut in its properties to alert them to excessive humidity or sudden temperature changes. With Minut’s real-time temperature monitoring and alerts, the company estimates it saves between $500 and $1,500 per mold-related issue.

“For us in Texas, Minut’s humidity sensor is super important because if the AC malfunctions, it could lead to a big mold risk that can be expensive to fix. With Minut, we know we are protected.” — Sébastien Long, Founder & CEO, Lodgeur

Discover how else Minut provides the team with peace of mind in Lodgeur's case study.

Key takeaways

‍Whether you’re already struggling with mold in your properties, or looking for ways to prevent it, the best time to take action is now. We’ve shared exclusive data from thousands of units to make sure you have all of the information you need to take on mold prevention. Here’s a quick recap of what you need to remember:

• Ignoring mold can lead to costs of up to $15,000 per unit, legal disputes, and property devaluation.
• High humidity levels (above 60%) create the perfect conditions for mold growth.
• Late summer and winter pose the highest threats due to humidity, storms, and condensation.
• Using smart technology will help you prevent mold from becoming a problem in the first place

Most importantly, ongoing monitoring is key. Minut’s real-time indoor climate alerts provide 24/7 insights into mold risks, allowing you to take quick action no matter where you are.