Renton basements get wet from Cedar River high water in the floodplain, and from groundwater and condensation on the hills above it. Remediation means drying the space, removing moldy porous materials and cleaning the structure once the source is handled. Call the number on this page to be connected with a local mold remediation company in Renton.
Renton and the Cedar River
Renton sits on the southeast shore of Lake Washington, about 11 miles from Seattle, where the Cedar River empties into the lake. The Cedar and Black rivers once flooded the town regularly, until the 1916 Lake Washington Ship Canal and Cedar River diversion cut the annual threat. The river can still rise. On Dec. 11, 2025 the Cedar River at Renton reached a record 18.22 feet, beating the old mark by more than a foot, and Maplewood residents sandbagged as river water seeped into backyards. The city's draft hazard mitigation plan notes considerable residential development in the Cedar River floodplain, including schools and senior residential communities, while the Green River valley floodplain is mainly commercial and industrial. Uphill, in places like West Hill, lower levels deal with groundwater, runoff and winter condensation instead. The median home was built in 1985.
Owner or renter: who handles what
| Step | Homeowner | Renter |
|---|---|---|
| First move | Stop the water and start drying | Tell the landlord in writing |
| Who hires the company | You do | Usually the landlord, who must keep the unit reasonably weathertight |
| If repairs stall | Get a second written bid | Report through Renton Responds; a city inspector verifies and the landlord gets 15 days to fix it |
| Proof it's fixed | An independent clearance check is good practice | For mold or water damage, the city may require the landlord to hire a third-party inspector and submit a report |
This is general information, not legal advice.
Signs to look for
- A musty smell in a lower level after heavy rain or high river levels
- Stains or a tide line on drywall
- Carpet that feels damp at the edges
- Spotting behind furniture against an exterior wall
- Condensation on cold pipes and windows during winter cold snaps
Timing and costs
Flood and seepage problems peak from late fall through early spring. Dry and remove damaged materials promptly, then rebuild once moisture readings are normal. Angi's Seattle cost guide lists basement mold remediation at $425 to $2,475; HomeGuide's 2026 national ranges are $1,500 to $6,000 partial and $6,000 to $15,000 full. Permits for rebuilding come from Building Customer Service under Renton Permit Services.
Basement Mold Removal questions in Renton
What should I do after floodwater gets into the basement?
Will homeowners insurance pay for basement mold?
Does the drywall in my finished basement have to come out?
How do I check a basement mold company in Washington?
More mold services in Renton
Basement Mold Removal nearby
Helpful guides
Sources
- Wikipedia: Renton, Washington
- Kent Reporter: Flood science, how December's atmospheric river soaked WA
- City of Renton: Draft Hazard Mitigation Plan (pdf)
- City-Data: Renton, WA houses
- City of Renton: Permit Services
- City of Renton: Rental Registration
- RCW 59.18.060: Landlord, Duties
- Angi: How Much Does Mold Remediation Cost in Seattle, WA?
- HomeGuide: How Much Does Mold Removal and Remediation Cost? (2026)
- Angi: How to Hire a Mold Remediation Company (separate testing and remediation)
- EPA: Homeowner's and Renter's Guide to Mold Cleanup After Disasters (pdf)
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