Mold Removal in Portland, OR: Older Homes, Basements, and Sewer Backups

The oldest housing stock in the metro

The Census Bureau's American Community Survey (2020 to 2024) puts the median year Portland homes were built at 1966. About 82,500 units, 27 percent of the total, date to 1939 or earlier, and 63 percent were built before 1980. For a house that old, the first questions are what is under the floor and how old the plumbing and roof are.

Age also changes how a repair is done. Federal rules treat housing built before 1978 as potentially containing lead-based paint, and the EPA requires lead-safe certification for contractors paid to disturb paint in those homes. Oregon DEQ requires an accredited asbestos survey before demolition or renovation of any residential building built before January 1, 2004. If a repair means opening walls or ceilings, ask the contractor how both rules will be handled before the work starts.

Basement floors, drains, and sewer backups

Water that shows up in a Portland basement does not always come from the soil. In neighborhoods served by combined sewers, heavy rain can push wastewater back up through floor drains. The City of Portland's Sewer Backup Prevention Program helps pay for a one-way backflow valve in the drain line. Residents of eligible combined-sewer areas pay the first $100 and the city pays the next $1,500, against a typical installation cost of about $1,600. Environmental Services staff can say whether an address qualifies.

After a backup, the city advises calling a plumber first to find the cause, since a blocked line on the property and a problem in the public sewer are handled differently. The same bureau runs a Basement Moisture Survey where residents can report sewer backups and groundwater seepage, which the city uses to plan projects. Materials soaked with sewage are a separate problem from a clean leak, and our page on flood and sewage damage explains how they are treated.

Rainfall varies by about ten inches across the city

NOAA's 1991 to 2020 normals record 36.9 inches of precipitation a year at Portland International Airport. A station at the KGW-TV site on the west side records 44.1 inches, and a volunteer station in outer southeast Portland records 46.8. A house on the wetter side of town carries more water through its roof, gutters, and below-grade walls than airport weather suggests.

Southeast Portland, Johnson Creek, and groundwater

Johnson Creek runs about 24 miles from farmland near Boring, through Gresham and southeast Portland, to the Willamette River in Milwaukie, and it drains a 54-square-mile basin. After heavy rain in water years 1996 and 1997, the U.S. Geological Survey documented two kinds of flooding. The creek itself rose for several days. Groundwater flooding, visible in the high flow of Crystal Springs Creek and an elevated water table near Holgate Lake, persisted for months to years.

A crawl space that fills during a storm and drains within days points to surface water. One that stays wet long after the rain stops points to groundwater, and the repair is different. Noting when the water arrives and how long it stays is the most useful thing a homeowner can bring to an inspection. Upstream, Gresham sits on the same creek.

Renters, landlords, and shared buildings

Forty-eight percent of Portland households rent, and a third of its housing units are in buildings with five or more units. Oregon law (ORS 90.320) requires a landlord to keep a dwelling habitable, and the list includes effective waterproofing and weather protection of roof and exterior walls and any ventilating facilities the landlord supplies. The statute does not name mold. A local tenant legal aid office can explain how it applies to a particular case. Owners and managers can read about our property manager and landlord services.

How the work is planned for Portland homes

Portland's median home dates to 1966, older than in any other city we serve, and 48 percent of households rent. A scope for a house like that names the lead-safe and asbestos-survey steps before any wall is opened, and it includes the moisture readings, dated photographs, and written findings that a landlord, manager, or insurer may ask for.

Portland neighborhoods we serve

• Sellwood-Moreland
• Multnomah (Multnomah Village)
• Laurelhurst
• Irvington
• Montavilla
• Foster-Powell
• Cully
• St. Johns
• Kenton
• Lents

Services for Portland homes and buildings

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