Basement Mold Removal in Renton, WA

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

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.