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Seattle, Washington mold guide

Mold Guide for Seattle, Washington

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

State law data last updated: 2026-02-02

Overview

Seattle receives roughly 39.3 inches of precipitation per year at an average of 53.7 F, which means it experiences a mix of wet spells and dry breaks.

Washington climate patterns, from seasonal storms to humidity shifts, interact with local conditions to influence indoor mold risk.

Seattle sits in the Puget Sound lowland with long wet seasons, so exterior surfaces stay damp for extended periods.

SDCI Code Compliance enforces housing maintenance and community standards.

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

Sources: [Washington - Climate | Britannica] | [Seattle Code Compliance] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Action Checklist

Get free access to the full guide

8-step checklist for immediate action

Seattle Home Inspection Checklist

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

In Seattle, code Compliance enforces housing maintenance and community standards across Seattle neighborhoods.

The division responds to complaints about housing conditions, land use, and property maintenance issues.

Sources: [Seattle Code Compliance]

  • With about 39.3 inches of annual rainfall, Seattle homes benefit from routine gutter cleaning and roof drainage checks.
  • Roof flashing, gutters, and downspout extensions.
  • Siding joints, window seals, and exterior caulk.
  • Crawlspace vents and vapor barriers.
  • Basement walls and floor drains.
  • Bathroom exhaust fans and vent ducts.
  • HVAC condensate lines and drip pans.
  • Under sink plumbing and cabinet bases.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Warning Signs of Mold in Seattle

Watch for these signs that moisture is lingering in Seattle homes and rentals:

  • Persistent window condensation in Seattle (annual average 53.7 F) is a common early indicator that indoor humidity is too high.
  • Musty odors after long rainy stretches.
  • Condensation that persists on windows or mirrors.
  • Peeling paint near baseboards or window trim.
  • Dark staining around ceiling corners.
  • Soft drywall around tubs or showers.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Mold Risk Factors in Seattle

These are the most common moisture drivers for homes and rentals in Seattle:

  • With roughly 39.3 inches of annual rainfall in Seattle, storm events and small leaks both matter.
  • Persistent winter rain keeps roofs and gutters saturated.
  • Short drying windows after leaks increase mold risk.
  • Moist marine air raises indoor humidity.
  • Crawlspaces and basements can stay damp without ventilation.
  • HVAC condensate and dehumidifier drains can overflow when clogged.

Sources: [Washington - Climate | Britannica] | [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Seattle Seasonal Risk Calendar

Winter

Heating systems work most of the year at 53.7 F average. Ventilate consistently to prevent moisture buildup on cold surfaces.

Spring

Lingering rain and cool temperatures slow drying.

Summer

Cool summers still bring rain. Inspect roof edges after storms.

Fall

Rains return. Recheck roof flashing and window seals.

Sources: [Washington - Climate | Britannica] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Seattle Moisture Playbook

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

After a Leak

Stop the leak, remove wet materials within 24 to 48 hours, and dry the area with airflow.

Monthly Maintenance

Inspect crawlspaces, clear condensate lines, and log indoor humidity.

Seasonal Tune Up

Before storm season, clear gutters and inspect flashing; about 39.3 inches of annual precipitation means small leaks can add up.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Mold Prevention in Seattle

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

  • Annual rainfall near 39.3 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 window seals before the wet season.
  • Service HVAC condensate drains annually.

Sources: [EPA Mold, Moisture, and Your Home] | [NOAA Climate Normals - SEATTLE TACOMA INTL AP, WA US]

Local Regulations

Some cities in Washington 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

Washington mold law snapshot

Washington has mold-specific rules in addition to general habitability standards.

Washington law establishes an implied warranty of habitability through RCW 59.18.060. Landlords must maintain premises fit for human habitation at all times during the tenancy. This includes keeping the property in substantial compliance with applicable codes affecting tenant health or safety, maintaining structural components in reasonably good repair, providing adequate weatherproofing, and maintaining plumbing, heating, and ventilation systems in reasonably good working order. While mold itself is not explicitly listed as a habitability violation, landlords must fix the conditions that cause mold: water leaks, moisture problems, and inadequate ventilation.

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

Frequently Asked Questions

What are the first signs of mold in a Seattle 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 Seattle?
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.
How does salt air affect mold growth in Seattle?
Salt air keeps humidity high and can wear down seals and caulk. Inspect exterior joints and ventilate crawl spaces regularly. See our prevention guide.
Are coastal homes in Seattle more prone to mold?
Fog, wind-driven rain, and elevated humidity put coastal homes at higher risk. Focus on ventilation, dehumidification, and exterior maintenance. Check our room-by-room guide.
What should I do about mold after a Seattle 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 Seattle 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.