ADU (accessory dwelling unit) Rules and Regulations in Tillamook County, OR (2026)

Building an ADU (accessory dwelling unit) on the Oregon Coast involves requirements that may not apply inland. In Tillamook County, coastal regulations, zoning overlays, and environmental conditions can change what a parcel can support. Below are the county-level basics; confirm the specific standards for your address before you design.

Where ADUs are allowed

County section 5.110 applies to lawfully established property in unincorporated community residential zoning districts. It allows one ADU with a primary dwelling and does not impose a minimum land area under that section. It is not a blanket rural-residential ADU allowance. Confirm the jurisdiction and use table; an address inside a city needs that city’s code review. Zoning overlays, environmental constraints, and coastal regulations can all affect whether an ADU is allowed on a given parcel and what form it can take.

Check the coastal overlays early. Two similar-looking lots can have very different paths depending on the overlays and constraints tied to each address.

Size, height, and setbacks

Section 5.110 limits floor area to the smaller of 800 square feet or 75% of the primary residence’s living space. A freestanding unit also has a footprint comparison. Height depends on the primary home and zone; detached and attached units have different setback rules. Have Planning check the proposed layout against the complete section before choosing a model.

Utilities: water, sewer, and septic

An ADU in Tillamook County needs a viable plan for water and sewer connections (or septic approval), plus electrical and utility hookups, and safe, compliant access to the structure. Drainage, soil conditions, and other environmental factors also feed into whether a site can support an ADU.

On many coastal and rural parcels, septic capacity and site conditions decide whether the project goes ahead. If the ground can’t support the wastewater system the ADU needs, the design doesn’t matter.

Salt air, wind, and long wet seasons also affect exterior selections. Wolf can include the optional Coastal Package in the project options when the property needs added protection for marine exposure.

Rental use

Section 5.110 prohibits transient lodging in the ADU. Confirm the permitted residential use before counting on rental income. Do not assume that a nearby vacation rental establishes permission for an ADU to operate the same way.

Permits and process

The permit path generally includes a site plan, utility coordination, erosion-control and stormwater planning, a complete permit packet, and any revisions requested by the county. Confirm current fees and review times directly with Tillamook County.

Start with Tillamook County Code Section 5.110 and the county’s ADU ordinance materials, and confirm which provisions are currently in effect before filing.

What Wolf checks first

For a Tillamook County project, we start with these questions before any floor plan:

1. What zone is the property in, and do any coastal or environmental overlays apply?
2. Is there an existing lawful primary dwelling on the site?
3. Can the property support the ADU’s water, sewer or septic, and electrical needs?
4. Does the intended occupancy comply with the ADU transient-lodging prohibition?
5. Can a modular unit be delivered, staged, and set safely on the site?
6. Does a smaller footprint avoid a constraint a larger model would trigger?

To compare Tillamook County with Clatsop, Lincoln, and the south coast, see Oregon coast ADUs and beach cottages.

Start with a free property evaluation

The published guidance doesn’t list every number you’ll need, so we check your parcel against the current Tillamook County requirements. Send us the property address and intended use. We will start with zoning, coastal constraints, utilities, and model fit.

Get a free Wolf property evaluation

This is general information, not legal advice. Confirm current rules, fees, and application requirements with Tillamook County or the city that has jurisdiction over your address.