Building permits, zoning and septic rules in Multnomah County, Oregon

Oregon requires a building permit to construct, enlarge, alter, repair or move a residential building or structure, including in unincorporated Multnomah County¹. The Oregon Residential Specialty Code applies statewide to applicable work on one- and two-family dwellings and townhouses¹¹. Multnomah County does not issue building permits; Portland Permitting & Development issues them for some unincorporated areas, while county Land Use Planning reviews building plans for zoning only, and septic permits stay with Portland's septic program countywide^2,12. Other unincorporated pockets may be administered by neighboring cities, so ask Land Use Planning which jurisdiction serves the parcel before applying^3,13. Certain detached, nonhabitable, one-story accessory structures under 200 square feet and under 15 feet in average roof height are exempt from a building permit, but electrical, mechanical or plumbing permits may still be required¹. In Portland-administered areas, a new single-family home, duplex or accessory dwelling unit needs a Certificate of Occupancy or Temporary Certificate of Occupancy before anyone moves in¹⁰.

Start with Multnomah County Land Use Planning at 503-988-3043 or land.use.planning@multco.us to confirm the parcel's jurisdiction and zoning¹³. When an owner applies for a building permit in an unincorporated area, the city refers the building plan to the county for zoning review; any required land-use permits must be approved before that plan is submitted¹². The county requires digital, scaled plans through its customer portal, including the application, site plan, floor plan, elevations and service-provider review forms, and the assigned planner sends a status update in 30 days¹². If Portland serves the parcel, contact Portland Permitting & Development at 503-823-7300 for the building permit². The county fee schedule effective July 1, 2026 lists $527 for a zoning plan check and $1,620 for a floodplain development permit; notice charges, deposits or other fees may also apply¹⁴. Inside Troutdale, the city handles building permits; Portland's septic program still handles septic permits countywide^4,15.

Multnomah County administers zoning for most unincorporated land, while some unincorporated pockets use city zoning under agreements³. County rural and Columbia River Gorge National Scenic Area zoning layers help identify the applicable rules; ask Land Use Planning to confirm the parcel’s designation^13,16. New-parcel minimums include 80 acres in Exclusive Farm Use, 20 acres in Multiple Use Agriculture and 5 acres in Rural Residential, subject to code exceptions⁶. Meeting a minimum acreage does not replace land-division approval: rural subdivisions are Category 1 Land Divisions⁶.

Dimensional rules vary by district. In MUA-20, structures are limited to 35 feet in height, though barns, silos and similar structures may be taller if set at least 30 feet from every property line⁶; yards are 30 feet in front, 10 feet at the side, 30 feet at the street side and 30 feet at the rear⁶. In the Multiple Use Forest zone, a dwelling built after August 14, 1980 must have at least 600 square feet of floor area and sit on a foundation with a building permit⁶. In MR-4, lot coverage is capped at 40 percent⁶. Farm use and accessory buildings generally need no Significant Environmental Concern (SEC) permit, but agricultural buildings need SEC-wr and/or SEC-sw approval in the West of Sandy River Planning Area and SEC-s approval within Metro’s 2009 jurisdictional boundary; that exemption does not replace a building permit^1,6.

Portland Permitting & Development administers septic permits and inspections throughout Multnomah County under agreements with the county and Oregon DEQ⁴. Where municipal sewer is unavailable, development must use onsite wastewater treatment, and the site needs enough usable space, required setbacks, adequate sewage-flow capacity, and suitable soil and water-table conditions¹⁷. Drainfield repairs, drainfield alterations and all new construction also need an approved Site Evaluation Report⁴. A licensed installer may build the system, or the property owner or owner's regular employee may do so after the septic installation permit is issued⁴. Complete applications are reviewed within 20 working days, and an application may be canceled if the applicant does not respond to a checksheet within 90 days⁴. Before final approval, every septic-tank permit needs an approved plumbing inspection of the sanitary line, plus approved electrical inspections when a pump is used⁴. Only about 1.5% of mapped county soils are rated “not limited” for a conventional drain field, so a site evaluation is essential; the soil rating does not mean septic is impossible¹⁸. Contact the septic program at 503-823-6892 or septic@portlandoregon.gov⁴.

Oregon allows camping-vehicle occupancy on private land with owner consent, adequate safe, approved water and sewage facilities, and compliance with applicable state and local installation standards⁷. Multnomah County zoning still controls the allowed use; ask Land Use Planning about the parcel before treating an RV as a residence^3,13. County-regulated campgrounds and RV parks allow temporary camping, not residential use; stays in MUA-20, RR, BRC, SRC and RC zones are limited to 90 days in any consecutive 12-month period unless state law provides otherwise, excluding the West of Sandy River and Urban Planning Areas⁶. County-regulated ADUs cannot be RVs, park-model RVs, yurts or similar designs not intended for permanent occupancy, or structures unable to meet construction standards⁶. Those ADUs cannot be rented for fewer than 30 consecutive calendar days, and owners must record a covenant¹⁹. In Portland-administered Dunthorpe, Pleasant Valley, Southern Border, West County and West Hayden Island, only 1 occupied RV or tiny house on wheels is allowed on a residential lot with a house; none is allowed on undeveloped lots²⁰. Manufactured homes are a separate question: Oregon allows occupying one on private land with the owner’s consent and adequate approved water and sewage⁷, while the county’s mobile home park rules in the LR-7 and LR-5 zones require a home built after June 15, 1976 with a state compliance insignia, set in a compliant mobile home space⁶. Outside those areas, we could not confirm a tiny-home primary-dwelling rule; ask Land Use Planning how the unit is classified¹³.

1. Ask Multnomah County Land Use Planning to confirm jurisdiction, zoning and applicable overlays^3,13,16.
2. Secure required land-use approval, then submit scaled digital plans for county zoning review through the customer portal¹².
3. Apply to the city issuing building permits for the address; call Portland Permitting & Development at 503-823-7300 when Portland serves the parcel².
4. Without sewer access, obtain a site evaluation and septic installation permit from Portland's countywide septic program⁴.
5. An eligible owner-builder can claim a narrow ceiling-height, room-size and temperature exemption, but needs a building permit, must intend to occupy the home and must build the structural components personally or with unpaid friends and relatives⁵. The owner-builder statement and licensed-subcontractor requirements also apply²¹. In Portland, a homeowner doing electrical, plumbing or mechanical work personally can pull those trade permits, provided the building is not for sale, lease or rent; electrical permits add a six-month resale lookback and a penalty of up to $500²².
6. Obtain a county driveway permit for new or altered access to a county road²³.
7. For Portland-issued building permits, schedule inspections before work is concealed; more than 180 days without an approved inspection causes expiration²⁴.
8. Before occupying a new home, duplex or ADU in a Portland-administered area, obtain a Certificate of Occupancy or Temporary Certificate of Occupancy¹⁰.

Confirm jurisdiction and zoning first because the county, Portland and neighboring cities divide responsibility by parcel location^3,13. Check septic feasibility early because only about 1.5% of mapped county soils are rated “not limited” for a conventional drain field¹⁸. If a private well is planned, a landowner who drills or alters it personally needs a state landowner permit, a $10,000 bond or letter of credit and a $550 fee before work begins⁸. Oregon generally requires a water-right permit to use groundwater, but domestic well use of no more than 15,000 gallons per day is among the listed exceptions⁹. Confirm access because a new or altered connection to a county road needs a driveway permit²³. About 38.4% of Multnomah County is federal land, so verify private ownership and boundaries¹⁸. If buying land to split, confirm the land-division category with Land Use Planning rather than relying on acreage alone^6,13. The typical annual home-insurance premium is about $1,181, and the median property-tax bill is about $5,061 at an effective rate near 1%¹⁸.