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St. Louis, Missouri mold guide

Mold Guide for St. Louis, Missouri

Local mold risk drivers, seasonal priorities, and next steps for homeowners and renters in St. Louis.

State law data last updated: 2026-02-02

Overview

St Louis receives roughly 41.7 inches of precipitation per year at an average of 57.4 F, which means it experiences a mix of wet spells and dry breaks.

The broader Missouri climate, including seasonal humidity peaks and storm activity, shapes the indoor moisture environment alongside local conditions.

St. Louis experiences hot, humid summers and cold winters with seasonal storms, so moisture risk swings between summer humidity and winter condensation.

The city offers residential property inspection requests for building code issues.

St. Louis residential property inspection requests help enforce building codes and safety standards.

This guide highlights local moisture drivers, seasonal risk, and prevention steps. For legal rights and landlord obligations, review the Missouri mold laws guide.

Sources: [Missouri Climate | Britannica] | [St. Louis Residential Property Inspection Request] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

Action Checklist

Get free access to the full guide

8-step checklist for immediate action

St. Louis Home Inspection Checklist

Common construction types in St. Louis affect where moisture problems develop. Here is how local building patterns shape what to inspect.

In St Louis, residential property inspection requests provide a path to document building code concerns.

Documenting moisture issues supports inspection follow up.

St. Louis residential property inspection requests help enforce building codes and safety standards.

Sources: [St. Louis Residential Property Inspection Request]

  • Roughly 41.7 inches of annual rain in St Louis means gutter maintenance and drainage checks should be part of the routine.
  • Roof flashing, gutters, and downspout extensions.
  • Attic insulation and ventilation near eaves.
  • Basement walls and sump pump pits.
  • Window frames and sills with condensation.
  • Bathroom exhaust fans and vent ducts.
  • Water heater pans and HVAC condensate lines.
  • Under sink plumbing and cabinet bases.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

Warning Signs of Mold in St. Louis

Watch for these signs that moisture is lingering in St. Louis homes and rentals:

  • At an annual average of 57.4 F, St Louis homes that show condensation on windows during warm months likely have an indoor moisture problem.
  • Musty odors after heavy rain.
  • Condensation that returns on windows each morning.
  • Peeling paint near baseboards or window trim.
  • Dark spotting near ceiling corners.
  • Soft drywall around tubs or showers.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

Mold Risk Factors in St. Louis

These are the most common moisture drivers for homes and rentals in St. Louis:

  • At about 41.7 inches of rain per year, St Louis storm events and small leaks both matter.
  • Thunderstorms bring heavy rain that tests roofs and gutters.
  • Humid summers keep indoor moisture elevated without dehumidification.
  • Freeze thaw cycles stress roof flashing and exterior joints.
  • Basements can stay damp after heavy rain.
  • Plumbing leaks behind fixtures can keep wall cavities wet.

Sources: [Missouri Climate | Britannica] | [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

St. Louis Seasonal Risk Calendar

Spring

Thunderstorms increase. Inspect roof edges and window seals after heavy rain.

Summer

At 57.4 F annually, air conditioning runs much of the year. Inspect condensate drains regularly and dehumidify lower levels.

Fall

Storms return. Clear gutters and check drainage.

Winter

Cold snaps drive window condensation.

Sources: [Missouri Climate | Britannica] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

St. Louis Moisture Playbook

Use this short playbook to stay ahead of common moisture problems in St. Louis.

After a Leak

Stop the water source, remove wet materials within 24 to 48 hours, and dry with fans plus a dehumidifier.

Monthly Maintenance

Clear condensate lines, track indoor humidity, and inspect under sinks and around tubs.

Seasonal Tune Up

Before storm season, clear gutters and inspect flashing; about 41.7 inches of annual precipitation means small leaks can add up.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

Mold Prevention in St. Louis

Use these priorities to keep indoor humidity low and avoid recurring growth:

  • Annual rainfall near 41.7 inches makes gutter maintenance and proper downspout drainage a top prevention priority.
  • Maintain indoor humidity between 30 and 50 percent.
  • Dry wet materials within 24 to 48 hours.
  • Vent bathrooms and kitchens outdoors.
  • Clear gutters and direct downspouts away from foundations.
  • Inspect roof flashing and window seals before storm seasons.
  • Service HVAC condensate drains annually.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - ST LOUIS LAMBERT INTL AP, MO US]

Local Regulations

Some cities in Missouri publish additional housing rules or enforcement guidance that can affect mold complaints.

Local regulations are available with the Mold Toolkit

1 city-specific regulations

State Laws and Rights

Missouri mold law snapshot

Missouri does not have a mold-specific statute, but habitability rules still apply.

Missouri recognizes an implied warranty of habitability in all residential leases through case law, not statute. This warranty was first established in King v. Moorehead, 495 S.W.2d 65 (Mo. Ct. App. 1973) and later adopted by the Missouri Supreme Court in Detling v. Edelbrock, 671 S.W.2d 265 (Mo. banc 1984). Under this doctrine, landlords must provide rental units with facilities and services vital to the life, health, and safety of tenants. The warranty does not require a perfect rental unit but does require the unit to be habitable and fit to be lived in. Hazardous mold, faulty wiring, exposed electrical components, rotting floors, and infestations are examples of conditions that may breach this warranty.

Use the full Missouri guide for tenant rights, landlord responsibilities, and remedies.

Frequently Asked Questions

What are the first signs of mold in a St. Louis home?
Musty odors, condensation on windows, peeling paint, and dark spots near vents or ceilings are common early signs. If symptoms persist after cleaning, schedule an inspection.
When should I hire a mold professional in St. Louis?
If the affected area is larger than about 10 square feet, if growth returns after cleaning, or if anyone has health symptoms, hire a pro. Use the DIY vs pro guide to decide.
Does St. Louis humidity make mold more likely?
High outdoor humidity slows drying after leaks, which raises risk. Active ventilation and dehumidification are key. Review prevention priorities for humid climates.
What should I do about mold after a St. Louis storm?
Stop the water source, remove wet materials within 48 hours, and run fans and dehumidifiers. Photograph damage for insurance. See the storm recovery guide.
Does flooding increase mold risk in St. Louis?
Flooding saturates walls, floors, and insulation. Mold can start within 24 to 48 hours. Dry the space quickly and consider professional help. See our flood cleanup guide.
Do temperature swings in St. Louis cause mold?
Large temperature changes can cause condensation in attics and crawl spaces. Seal penetrations and maintain balanced airflow. See our attic mold guide.