Renter Guides
Most mold in apartment homes around Seattle starts the same way every winter: warm, damp indoor air meets a cold window or an outside wall, and water collects. Left alone for a few weeks, that water feeds the black spots you find on window frames, behind the couch or in the corner of the bathroom ceiling.
The good news is that winter condensation is predictable, and most of it is easy to manage. This guide explains why it happens here, how to tell condensation from a real leak, the habits that keep mold away, what Washington law asks of renters and landlords, and how to report a problem so it gets fixed quickly.
The short version
Condensation forms when warm, moist indoor air touches a surface colder than the air's dew point, usually a window or an outside wall. Seattle winters are cool and wet for months at a time, so windows stay cold while showers, cooking and drying laundry keep adding moisture inside.
Our mild weather is part of the problem. NOAA’s 1991 to 2020 normals for Sea-Tac show December highs near 47 degrees and lows near 37, with rain on about 18 days in each of November, December and January. Outdoor air rarely dries out, so an open window does less than in a crisp, cold climate.
Inside, showers, cooking, laundry on a rack and houseplants all add water to the air. In a compact apartment that moisture settles on the coldest surfaces first: glass, window frames, closets on outside walls and corners behind furniture.
November through January brings about 17.8 inches of rain on average, close to half of Sea-Tac’s yearly 39 inches. That is when windows fog most and small habits matter most.
Why late fall is the time to start
Condensation shows up the first week the heat goes on and windows stay shut. Start these habits now and you are ahead of the wettest months instead of cleaning up in January.
Condensation forms on the room side of a cold surface and follows your routine. A leak brings water from somewhere else, like the roof, a pipe, a window seal or the unit above, and usually leaves a stain that grows in one spot. The fix, and who handles it, differ.
Condensation (usually a habit and airflow issue)
A leak (report it right away)
Not sure? Report it anyway and describe what you see. A slow drip is far easier to fix in October than in February.
The most common signs are a musty smell and small black, green, gray or white specks on damp surfaces. The Washington State Department of Health notes that you usually do not need to test for mold, because in most cases you can see it or smell it. Look and sniff in the places moisture collects:
Mold can also hide inside walls, ceilings or under carpet. The EPA says to suspect hidden mold if a space smells moldy but you cannot see the source, which is worth a maintenance request on its own.
Please do not paint over it
Painting, caulking or hanging something over a mold spot hides it without fixing the moisture behind it, and it can make the real cause harder to find. Clean small surface spots, and report anything that keeps coming back.
On health, the CDC says damp, moldy spaces affect people differently, and some not at all. People with asthma, allergies or lung conditions can be more sensitive. If you have a health concern, talk with your doctor.
Prevent mold by controlling moisture. Keep indoor humidity below 60 percent and ideally between 30 and 50 percent, run bathroom and kitchen fans every time, keep steady heat in every room, open blinds during the day, leave a gap behind furniture on outside walls and wipe window condensation each morning.
As the EPA puts it, the key to mold control is moisture control. You do not need special products, just a few steady habits and a way to measure how damp your air is.
A hygrometer (humidity meter) is an inexpensive gadget the EPA notes is sold at many hardware stores. Set it in a living room or bedroom, away from the bathroom, check it morning and evening for a few days, then enter your reading below.
Check your indoor humidity
Enter the relative humidity (RH) reading from your hygrometer.
Ranges follow EPA guidance: below 60 percent, ideally 30 to 50 percent. One reading right after a shower or cooking will run high, so use your typical reading.
Above 60 percent most days? Start with fans and heat. If it stays high, a portable dehumidifier can help; the EPA lists them as a moisture tool. A bathroom fan that is weak or not pulling steam out is a repair request, not something to live with.
Cold rooms have cold windows, and that is where condensation forms first. The Department of Health asks renters to run heat and ventilation to reduce condensation, and the EPA lists raising air temperature as a fix. A modest, steady setting in every room beats big swings.
Daily and weekly habits that stop condensation
0 of 15 done
Every day
Every week
Once a season
These habits work in nearly any building, from an older brick walk-up on Capitol Hill to a newer mid-rise. Older single-pane or aluminum windows fog more, so the morning wipe matters most there.
Pro tip: give the shower fan a head start
Turn the bathroom fan on before you start the water, not after the mirror fogs. Keeping steam from building up in the first place is much easier than clearing it later.
Clean and dry a small spot on a hard surface, then deal with the moisture behind it. The EPA and the Washington State Department of Health both treat areas under about 10 square feet as small enough to handle yourself. A line of black on shower caulk or a few spots on a window frame are well under that.
Report it instead of cleaning it if the mold is on drywall, carpet or a ceiling, covers a larger area, came from a leak, or returns soon after cleaning. Mold that keeps coming back means the moisture source has not been found yet.
Resident portal
Submit a maintenance request with a photo. It goes straight to the maintenance queue and creates a record you can follow.
In Washington, responsibility usually follows the source of the moisture. Landlords must keep the unit weathertight and keep roofs, walls, plumbing and heating in good repair, so leaks are theirs to fix. Renters must use fixtures properly, keep the unit clean and avoid causing damage, which covers everyday ventilation habits.
Under RCW 59.18.060, the landlord must keep the unit fit to live in, maintain roofs, floors and walls, keep it reasonably weathertight, and keep plumbing, heating and supplied fixtures working. Landlords must also give tenants Department of Health information about indoor mold, in writing or posted in a visible public spot, and new tenants get it at lease signing.
That information duty is the only place the section names mold, which is why the Department of Health tells renters to focus on the water problem. Under RCW 59.18.130, tenants must keep their unit clean and sanitary, use fixtures properly and not damage the unit through carelessness.
| Situation | Usually handled by | Why |
|---|---|---|
| Running bathroom and kitchen fans | Renter | Proper use of supplied fixtures (RCW 59.18.130) |
| Keeping heat on and wiping window condensation | Renter | DOH asks renters to run heat and ventilation to reduce condensation |
| Cleaning small spots on hard surfaces | Renter | Keeping the unit clean and sanitary (RCW 59.18.130) |
| Reporting leaks and moisture buildup in writing | Renter | DOH advises prompt written notice to the landlord |
| Roof, wall, window or siding leaks | Landlord | Weathertight and structural duties (RCW 59.18.060) |
| Plumbing leaks and broken exhaust fans | Landlord | Keeping plumbing and supplied fixtures working (RCW 59.18.060) |
| Heating system that does not work | Landlord | Heat and heating facilities (RCW 59.18.060) |
| Giving tenants DOH mold information | Landlord | Required by RCW 59.18.060 |
| Damage caused by a tenant’s own actions | Renter | No landlord repair duty for tenant-caused conditions (RCW 59.18.060) |
| Allowing access for repairs with proper notice | Both | Landlord gives 2 days’ written notice; renter may not unreasonably refuse (RCW 59.18.150) |
A failed window seal is a maintenance item; fog after a long shower with the fan off is a habit item. When in doubt, report what you see and let maintenance sort out which it is.
Key point
When you describe the problem, lead with the water: “there is a stain growing on the ceiling after rain” or “the bathroom fan is not pulling steam out.” The Department of Health notes that building officials focus on the source of the water problem, and so does a good repair.
Report it in writing, with photos, as soon as you notice it. The Department of Health asks renters to notify landlords promptly and in writing of any water leaks or moisture buildup, and the EPA gives renters the same advice. For Pacific Crest Real Estate residents, the resident portal is the written record: requests go directly to the maintenance queue and you can see their status.
Pacific Crest Real Estate provides round-the-clock emergency maintenance coordination for water intrusion, flooding and burst pipes. If water is actively coming in, call (206) 812-9150 instead of waiting on a portal message.
Once a landlord receives written notice of a defective condition, RCW 59.18.070 says they must begin fixing it as soon as possible, and no later than set time limits unless circumstances are beyond their control. Those limits are about starting the work, not finishing it, because some repairs take longer to complete.
A typical moisture repair goes in stages: find the source (the unit above, the roof, a window seal or a fan), fix it, dry the area, then clean or replace damaged materials. The EPA says water-damaged areas should be dried within 24 to 48 hours to prevent mold, one more reason to report water fast.
Under RCW 59.18.150, landlords give at least two days’ written notice before entering for repairs, with a time window and a number to reschedule. In an emergency they may enter without notice. Renters may not unreasonably refuse repair access, so agreeing on a time is the quickest way forward.
These quick questions spot the one or two habits that would make the biggest difference this winter.
Is your apartment at risk of mold?
8 quick yes or no questions
1. Do you run the bathroom fan during every shower and for a while after?
2. Do you use the range hood or kitchen fan when you cook?
3. Do you usually dry laundry on racks inside the apartment?
4. Do you wake up to water running down the inside of your windows most mornings?
5. Is any furniture pushed tight against an outside wall?
6. Do you keep the heat off in rooms you do not use?
7. Is your indoor humidity usually above 60 percent?
8. Is there a drip, stain or leak you have noticed but not reported yet?
Answer the questions above
Answer for a typical week this fall.
Scored lower than you hoped? Most of these change in a day, and anything pointing to a repair, like a weak fan, is what maintenance is for.
First, ask for an update in the same portal request or reach the office through the contact page. Most delays are missed messages, access issues or parts on order.
If a repair stays unresolved, Seattle renters can contact the Seattle Department of Construction and Inspections (SDCI). It enforces the city’s Housing and Building Maintenance Code, which covers roofs, walls, ventilation and heating, and renters can ask for a housing inspection. Use the Make a Complaint form on the Seattle Services Portal, or the Violation Complaint Line at (206) 615-0808 for time-sensitive issues.
Under RCW 59.18.240, a landlord may not retaliate against a tenant in compliance with the law who, in good faith, reports health or safety code issues to a government authority or asserts their rights.
About Seattle's rental inspections
Seattle’s Rental Registration and Inspection Ordinance (RRIO) requires rentals to register and be inspected at least once every 5 to 10 years, with at least two days’ notice to renters. It is a routine checklist; for a specific repair problem, use the SDCI complaint route above.
Still apartment hunting? Ask about fans, heating and maintenance requests on tours. Our Seattle renter guide covers applications and deposits, and the neighborhood guide compares areas.
Some morning fog on the glass is common in Seattle winters, especially in older buildings. It becomes a problem when water runs onto the sill daily or mold starts on the frame. Fans, steady heat, open blinds and a morning wipe usually bring it under control.
It depends on the moisture source. Landlords must keep the unit weathertight and keep plumbing, heating and fixtures working, so leaks and broken fans are theirs. Renters must use fixtures properly, keep the unit clean and avoid damage. Landlords must also give tenants Department of Health mold information.
For a small spot on a hard surface, usually yes. The EPA and the Washington State Department of Health describe areas under about 10 square feet as small enough to clean yourself. Scrub with detergent and water, dry completely and never mix bleach with ammonia. Report mold on drywall, carpet or ceilings, and anything that keeps coming back.
Washington law sets limits for starting repairs after written notice. Most moisture issues fall under the 10-day limit. Loss of water, heat or electricity, or an imminent hazard to life, has a 24-hour limit; loss of a refrigerator, range or major plumbing fixture, 72 hours. These are deadlines to begin work, not finish it.
Usually not. The CDC does not recommend routine mold testing, and the Washington State Department of Health says that in most cases you can see or smell mold. What matters is finding and fixing the water source. If you see spots, smell mustiness or notice a stain, report it with photos through the resident portal.
Looking for a well-kept place to rent?
Pacific Crest Real Estate manages apartment homes across Seattle, the Eastside and the Puget Sound region, with maintenance requests handled through one simple resident portal.
Sources
Verified as of October 2026. This is general information, not legal advice. Laws and city processes change, so check the linked sources. Health information is general CDC, EPA and WA DOH guidance; ask your doctor about personal concerns.
