Handling Mold Reports in Your Rental Property: A Step-by-Step Guide

Handling Mold Reports in Your Rental Property: A Step-by-Step Guide

Mold is one of those words that can make any rental housing provider's stomach drop. Renters worry about their health, Housing Providers worry about costly remediation, and sometimes panic sets in before the situation is even fully understood. But before you call in an expensive mold testing company or hire a professional cleanup crew, it’s essential to take a deep breath and assess the situation rationally.

Most mold issues in rental housing can be resolved with a few key steps: identifying the source of moisture, addressing ventilation or leaks, and using the proper cleaning methods. And here’s something many people don’t realize—the California Department of Public Health (CDPH) does not recommend mold testing at all. If you can see or smell mold, that’s enough evidence to take action. Testing for “levels” and “types” of mold doesn’t change the fact that moisture is the real problem, and that’s what needs to be fixed.

This guide will walk you through exactly what to do when a tenant reports mold—what steps to take, what to avoid, and when (if ever) you need to bring in a professional.

1. Stay Calm and Gather Information

Mold reports can be alarming, but panic leads to unnecessary expenses and sometimes poor decision-making. Before hiring a professional mold inspector or remediation company, gather key details from the tenant to assess the situation rationally.

Questions to Ask the Tenant:

• Where is the mold located? (e.g., bathroom ceiling, under the sink, near a window)
• How long have they noticed it? (Did it just appear, or has it been there for months?)
• Is there a known water leak nearby? (Recent plumbing issues, roof leaks, or condensation buildup?)
• Is there a musty odor? (Even if mold isn’t visible, a damp or earthy smell is a key indicator.)
• Have they tried cleaning it? (If so, what happened? Did it return quickly?)

Why This Step is Important:

• Prevents knee-jerk reactions. Some landlords immediately call mold testing companies, which can be costly and unnecessary.
• Helps identify the likely cause. Mold needs moisture to grow, so understanding the conditions helps determine if there’s an underlying issue.
• Determines if it’s an isolated issue or a larger problem. A small patch in a bathroom might just be due to poor ventilation, while mold in multiple rooms could indicate a bigger moisture problem.

Next Steps After Gathering Information:

• If the mold is minor (less than 10 sq. ft.), inspect it yourself first before escalating.
• If there’s an active water leak, fix the source of moisture before addressing the mold itself.
• If the mold covers a large area, document it with photos and assess whether professional remediation is needed.

2. Inspect the Area

Once you've gathered information from the tenant, the next step is to personally inspect the affected area. This helps confirm whether the issue is minor and easily managed or if it requires professional intervention.

Key Things to Look For:

✅ Visible Mold Growth:

• Is the mold only on the surface (e.g., bathroom tile, window sills), or does it appear embedded in walls, ceilings, or floors?
• Is it a small patch (less than 10 sq. ft.) or more widespread?
• Are multiple areas in the unit affected?

✅ Signs of Moisture Problems:

• Leaks: Check for dripping pipes, roof leaks, or appliance leaks (e.g., under sinks, near the water heater).
• Condensation: Look for excessive moisture on windows, walls, or cold surfaces (often due to poor insulation or ventilation).
• Dampness: Touch walls or ceilings to see if they feel damp or soft—water damage often precedes mold growth.
• Peeling Paint or Bubbling Drywall: These can indicate hidden moisture inside the walls.

✅ Ventilation Issues:

• Are exhaust fans working properly? Bathrooms and kitchens should have functioning ventilation to reduce moisture buildup.
• Are windows regularly opened? Poor airflow can contribute to humidity and mold growth.

What to Do During the Inspection:

🔹 Take Photos – Document the mold and any moisture-related damage. This is useful for record-keeping and communicating with tenants.
🔹 Use a Moisture Meter (if available) – These inexpensive devices can measure the moisture content of walls, ceilings, and floors, helping you determine whether water is present behind surfaces.
🔹 Check Nearby Units (If Applicable) – In multi-unit buildings, mold can spread from neighboring units if there’s a common source of moisture.

Common Misconception: Mold Testing vs. Moisture Testing

• Mold testing is rarely necessary. If mold is visible or odorous, the California Department of Public Health (CDPH) states that testing isn’t required.
• Moisture testing is more useful. If you suspect mold inside walls or ceilings, testing for hidden moisture (not mold levels) can help locate the source of the problem.

Next Steps After Inspection:

• If the mold is minor and caused by condensation or lack of ventilation, tenant education and improved airflow may resolve the issue.
• If there is an active leak, it must be repaired before mold remediation begins.
• If the mold appears structural or widespread, professional remediation may be needed.

3. Address the Moisture Source First

Mold is a symptom, not the root cause—the real issue is excess moisture. Cleaning mold without fixing the moisture problem guarantees it will come back.

Common Sources of Moisture and How to Fix Them

✅ Plumbing Leaks

• Check for dripping faucets, under-sink leaks, water stains on ceilings, or running toilets.
• Fix immediately—even small leaks can create persistent damp conditions.
• If there’s damage, replace water-damaged materials like drywall or cabinetry to prevent future mold growth.

✅ Roof or Window Leaks

• Look for water stains on ceilings or walls, especially near windows.
• Check caulking and weather stripping—seal any gaps around windows and doors.
• For roof leaks, inspect the attic (if accessible) for signs of moisture and address it before it worsens.

✅ Condensation Buildup

• Common in bathrooms, kitchens, and cold exterior walls.
• Increase airflow by using exhaust fans, opening windows, or running ceiling fans.
• Consider dehumidifiers if the unit has persistent humidity issues.

✅ Poor Ventilation

• Bathrooms and kitchens must have working exhaust fans vented outside (not just recirculating).
• If tenants aren’t using fans, encourage them to run them for at least 30 minutes after showers or cooking.
• If humidity is high, keeping doors open between rooms can improve airflow.

✅ Blocked or Inadequate Airflow

• Heavy furniture or curtains blocking air vents or baseboard heaters can lead to moisture buildup.
• Check HVAC filters—dirty filters reduce airflow, which can contribute to humidity problems.
• If tenants use humidifiers, ensure they’re not overusing them (keeping indoor humidity below 60% helps prevent mold).

What NOT to Do

🚫 Don’t Just Clean the Mold Without Fixing the Moisture – It will return if the damp environment remains.
🚫 Don’t Assume Mold is the Tenant’s Fault – While lack of ventilation can contribute, moisture problems often stem from structural issues or appliance malfunctions.
🚫 Don’t Skip Repairs to Save Costs – Small leaks lead to expensive problems later if left unaddressed.

Next Steps After Fixing the Moisture Issue:

• If the mold is minor, clean it with an appropriate product (we’ll cover this in Step #4).
• If materials like drywall, carpet, or wood are heavily damaged, they may need to be replaced.
• Educate tenants on how to prevent future moisture issues, reinforcing proper ventilation habits.

4. Cleaning Small Areas of Mold Properly

Once the moisture source is fixed, you can safely clean small areas of mold (less than 10 square feet). However, using the wrong cleaning methods—like bleach—can be ineffective or even make the problem worse.

Best Practices for Safe Mold Cleanup

✅ Wear Protective Gear

• Use gloves, goggles, and an N95 mask to prevent inhaling mold spores.
• Open windows for ventilation while cleaning.

✅ Choose the Right Cleaning Solution

🔹 What Works Best:

• Detergent & Water: Works for non-porous surfaces like tile, tubs, and countertops.
• White Vinegar (Undiluted): Penetrates porous surfaces like drywall and wood and kills about 80% of mold species.
• Hydrogen Peroxide (3% or higher): Effective for mold on fabric, wood, or drywall.
• Baking Soda & Water Paste: Gentle, non-toxic option that also helps absorb moisture.
• Commercial EPA-Approved Mold Cleaners: Contain antimicrobial agents for stubborn mold.

🔹 What NOT to Use:

🚫 Bleach – Bleach is not recommended because it is hazardous and not any more effective than safer methods. It can harm your health by irritating the skin, eyes, nose, and throat, and cause breathing problems and injuries. It can also damage clothing, shoes, and other materials. It will not kill mold unless you have cleaned the area first and removed the mold, and then bleach is not necessary. Bleach does not keep mold from growing back.
🚫 Ammonia – It’s toxic and ineffective on porous materials.
🚫 Mixing Chemicals – Never mix bleach and vinegar or bleach and ammonia—they produce dangerous fumes.

✅ How to Clean Mold Safely

1. Spray the affected area with your chosen solution (vinegar, peroxide, or detergent mix).
2. Let it sit for at least 10-15 minutes—this allows it to break down the mold.
3. Scrub with a brush or sponge for non-porous surfaces.
4. For porous materials (wood, drywall): Wipe gently but avoid oversaturating—excess moisture encourages mold regrowth.
5. Dry the area completely using fans or dehumidifiers.
6. Dispose of contaminated rags or sponges in a sealed bag.

When to Replace Instead of Clean

• If drywall, carpet, or ceiling tiles are heavily contaminated, it’s better to remove and replace them rather than attempt cleaning.
• Wood surfaces may need sanding if mold has penetrated deeply.
• If mold is inside HVAC ducts, a professional should inspect and clean them.

Next Steps After Cleaning:

• Monitor the area for a few weeks to ensure no regrowth.
• Continue proper ventilation to prevent future moisture buildup.
• If mold returns despite fixing the moisture issue, consider hidden water damage inside walls or flooring.

5. When to Call in a Professional

While many small mold issues can be handled independently, there are situations where professional intervention is necessary. Knowing when to call in experts can prevent costly mistakes, legal liability, and recurring mold problems.

Signs That You Need a Professional Mold Remediation Service

✅ The Affected Area is Large

• The EPA recommends professional remediation for mold growth covering more than 10 square feet.
• If mold is spreading rapidly despite cleaning and moisture control efforts, it may indicate a hidden moisture problem.

✅ Mold is in HVAC Systems

• If mold is growing inside ductwork, air conditioning units, or heating systems, it can spread throughout the entire property.
• Specialized HVAC cleaning is required to prevent airborne mold spores from recirculating.

✅ Mold is Inside Walls, Ceilings, or Flooring

• Water-damaged drywall, insulation, or subflooring can trap mold in places you can’t reach.
• If you smell mold but can’t see it, there may be hidden growth behind walls or under flooring.

✅ The Property Has Had Flooding or Major Water Damage

• Any mold growth resulting from flooding, roof leaks, or burst pipes may require remediation, especially if water has been sitting for more than 48 hours.
• Porous materials (drywall, carpet, ceiling tiles) that were soaked should generally be removed and replaced.

✅ Recurring Mold Despite Cleaning

• If mold keeps coming back in the same place, it could mean:
• The moisture problem hasn’t been fully resolved.
• There is a larger colony of hidden mold behind walls or floors.
• The cleaning method used was ineffective (e.g., bleach on porous materials).

✅ Health Complaints from Tenants

• If tenants report persistent respiratory issues, allergies, or other mold-related health concerns, professional assessment may be necessary.
• The California Department of Public Health (CDPH) recognizes mold as a potential health hazard, and failing to address a serious issue could lead to legal liability for landlords.

Who to Call for Help

• Licensed Mold Remediation Contractors – Handle removal, containment, and safe disposal of mold-infested materials.
• Certified Industrial Hygienists (CIH) – Conduct mold inspections and air-quality testing if needed.
• HVAC Professionals – Clean and disinfect ductwork if mold is present.
• Plumbers or Roofers – If leaks or water intrusion are the source of mold, a licensed contractor should repair the issue before remediation.

When You Don’t Need a Professional

🚫 Avoid hiring a mold testing company unless absolutely necessary.

• CDPH states that mold testing is usually unnecessary. If mold is visible or has a strong odor, that’s sufficient evidence to take action.
• Some mold testing companies overstate risks or upsell unnecessary services—focus on fixing the moisture source and removing visible mold.

Next Steps After Professional Remediation

• Ensure the contractor completes repairs to prevent future mold growth.
• Request before-and-after documentation to confirm the issue was resolved.
• Educate tenants on prevention strategies to avoid future mold problems.

6. Mold Testing is Unnecessary…Most of the Time

Many landlords assume that hiring a mold testing company is a critical first step, but testing is a waste of money in most cases. The California Department of Public Health (CDPH) explicitly states that if mold is visible or there’s a musty odor, testing is unnecessary—removal and moisture control should be the focus instead.

Why Mold Testing is Typically Not Needed

✅ Visible Mold is Enough Evidence

• You don’t need a lab report to confirm what you can see and smell. If mold is growing on walls, ceilings, or floors, it needs to be removed, regardless of the specific mold type.

✅ There Are No Legal Standards for 'Safe' Mold Levels

• Unlike lead or asbestos, there is no government-established "safe" level of mold exposure.
• Even if a test shows "high mold levels," it doesn’t change the fact that visible mold should be removed and moisture issues corrected.

✅ Testing Doesn’t Identify the Root Cause

• Lab results might tell you the type of mold present, but they don’t explain why mold is growing.
• Moisture testing (checking for leaks or humidity issues) is far more useful than air or surface mold testing.

✅ Mold Spore Levels Fluctuate Naturally

• Mold spores exist everywhere, both indoors and outdoors.
• A test might detect mold spores in the air, but that doesn’t mean the property has a hazardous mold problem—it just means mold is present, as it is in every building.

When Mold Testing Might Be Useful

🚨 If There’s an Insurance or Legal Dispute

• Some insurers require mold testing before approving remediation claims.
• If a tenant is making a legal claim for mold-related health issues, testing could be used as part of documentation—but should only be done by a neutral third party (not a mold remediation company trying to sell services).

🚨 If Mold is Suspected but Not Visible

• If a strong, musty smell persists despite cleaning, and there’s no visible mold, air sampling might help locate hidden mold.
• Better alternative: Use a moisture meter to check walls, ceilings, and floors for hidden dampness instead of paying for an expensive mold test.

How to Respond if a Tenant Demands Mold Testing

• Explain CDPH guidelines: Testing isn’t required when mold is visible or can be smelled.
• Focus on fixing moisture issues: Show that you’re addressing the root cause of the problem.
• Offer a professional inspection if necessary: A licensed contractor can check for leaks and structural damage without unnecessary mold testing.

Next Steps After Skipping the Test:

• Fix the moisture issue. (As discussed in Step #3)
• Clean or remove affected materials. (Step #4)
• Monitor the area for regrowth.
• Educate tenants on prevention. (Covered in Step #7)

7. Educating Tenants on Prevention

Even after mold is removed and the moisture issue is fixed, prevention is key to ensuring it doesn’t return. Since mold thrives in damp environments, tenants play a crucial role in maintaining proper ventilation and moisture control inside the unit.

Key Prevention Tips for Tenants

✅ Use Bathroom and Kitchen Exhaust Fans

• Run bathroom fans for at least 30 minutes after showers to reduce humidity.
• Always use the stove hood vent when cooking or boiling water.

✅ Keep Windows Open When Possible

• In humid or poorly ventilated areas, opening windows even for 15–30 minutes a day can help reduce condensation.
• If a unit has single-pane windows, encourage tenants to wipe away condensation in winter months.

✅ Run Ceiling Fans or Portable Fans

• Keeping air circulating prevents stagnant moisture buildup, especially in small rooms with little airflow.

✅ Avoid Blocking Air Vents or Baseboard Heaters

• Furniture or heavy curtains blocking vents or heating sources can create moisture pockets where mold thrives.

✅ Report Leaks or Plumbing Issues Immediately

• Leaky faucets, running toilets, and roof leaks should be reported as soon as possible.
• Small leaks can lead to big mold problems if ignored.

✅ Keep Indoor Humidity Below 60%

• If a tenant uses a humidifier, ensure it’s not being overused—excessive humidity can cause mold.
• Consider providing tenants with a low-cost humidity gauge to monitor levels.

✅ Be Mindful of Damp Laundry and Shower Curtains

• Wet clothes should be dried promptly—never left in piles.
• Encourage tenants to keep shower curtains closed after use so they dry properly.

How to Communicate These Tips Effectively

📌 Include a Mold Prevention Guide in Lease Packets – A simple one-page handout can prevent misunderstandings later.
📢 Post Reminders in Common Areas – If the unit is in a multi-family building, signs in laundry rooms, bathrooms, or near vents can help.
📬 Send Seasonal Reminders – A quick email before winter or rainy seasons can remind tenants to check for condensation or leaks.

Final Takeaway for Landlords

• Mold prevention is a shared responsibility—tenants should maintain proper ventilation, while landlords must address leaks and structural moisture issues.
• Document tenant education efforts—if a mold issue arises later, showing that you provided prevention guidance can help mitigate liability.

Mold problems don’t have to turn into full-blown disasters. By staying calm, investigating the issue, and addressing moisture first, you can resolve most mold concerns without unnecessary costs or legal headaches.

The key takeaway? Mold grows where moisture lingers. If you fix the moisture problem—whether it’s a leak, poor ventilation, or condensation buildup—you stop mold from coming back. Educating tenants on prevention, responding to reports quickly, and knowing when professional help is truly needed will keep you ahead of the game.

At the end of the day, good property management is about proactive problem-solving, not panic. Handle mold issues confidently, and you’ll keep your rental unit and renters in good shape.