Do I need a permit for an accessory dwelling unit (ADU) in
Tigard, Oregon?

Tigard ADU permits — the key details

Oregon state law (ORS 197.312) mandates that Tigard allow at least one ADU per single-family residential lot as a permitted use, with no discretionary review (variance or conditional use). Tigard goes further: the city allows both detached ADUs and attached ADUs (including garage conversions and junior ADUs). A detached ADU is any dwelling unit of up to 800 square feet on a single-family lot; a junior ADU is an interior conversion of 400-600 square feet with no separate kitchen (just a kitchenette). The state law also eliminates off-street parking requirements for ADUs entirely — Tigard cannot require you to build additional parking for the ADU. This is radically different from neighboring jurisdictions like Beaverton, which still impose parking and owner-occupancy rules. However, 'permitted use' does not mean 'exempt from permit.' You must pull a building permit, submit plans, pass design and building review, and complete all inspections. Tigard's building code is the 2021 International Building Code and International Residential Code; fire and plumbing follow current IBC/IRC sections (no grandfathering). Your ADU must meet all baseline setbacks, easement, and utility requirements that apply to principal residential structures.

Setback and lot-size rules are where Tigard adds local specificity. A detached ADU must be set back at least 5 feet from the side lot line and 10 feet from the rear lot line (per Tigard Code 18.86). On smaller lots (under 7,500 square feet), Tigard allows a variance application to reduce the rear setback to 5 feet if the ADU is 600 square feet or smaller. This is critical: if your lot is less than 75 feet deep, a standard detached ADU won't fit without a setback variance, which adds 4-6 weeks and $500–$1,000 to the timeline and cost. Attached ADUs (above garage, side yard conversion, or junior ADU carved from the principal house) face less stringent setback relief because they don't create two separate massing elements. Tigard also imposes minimum lot area triggers: an ADU on a lot under 6,000 square feet must not exceed 600 square feet; lots 6,000-7,500 square feet can support up to 750 square feet; lots over 7,500 square feet can go to 800 square feet (or 900 if detached from the principal structure). These thresholds are codified in Tigard Code 18.86.040 and are non-negotiable; they directly affect your schematic design.

Utility and infrastructure requirements are the second biggest variable in Tigard ADU permitting. Detached ADUs must have separate utility connections: separate water meter, separate electrical service (or a compliant sub-meter), separate sewer lateral, and separate gas service (if applicable). This is not optional and is often the costliest part of ADU buildout — running a water line and sewer lateral across the property can run $8,000–$15,000. Attached ADUs (e.g., junior ADU inside the principal house or a garage conversion) can share the principal residence's utilities via sub-meter for electricity and a demising wall or separate meter for water/sewer. Tigard's planning staff require a utility plan (scaled drawing showing meter locations, service entry points, and easement paths) as part of the permit application; if utilities aren't shown, the city returns the application marked 'incomplete.' Similarly, if your lot is in a fire-prone zone (wildland-urban interface, or WUI — check your parcel on the Tigard GIS map), sprinklers may be triggered by the combined floor area of the principal residence and ADU. The Willamette Valley does not typically require sprinklers for under 5,000 total square feet, but if your principal home is 2,500 square feet and you add a 700-square-foot ADU, you may cross the threshold. Confirm with Tigard Planning before finalizing your design.

Drainage, foundation, and soils are especially relevant in Tigard because of the Willamette Valley's volcanic and alluvial soils. Tigard frost depth is 12 inches in the valley and up to 30 inches in the eastern rural areas; your footing depth must be 18-20 inches minimum if you're in the valley, 36-42 inches if you're east of I-5. Many Tigard lots have clay-heavy subgrades and seasonal water tables — if your ADU is detached and within 10 feet of a storm drain easement or within 25 feet of a stream, the city requires a geotechnical report or SWPPP (Stormwater Pollution Prevention Plan). This is triggered automatically during plan review if the parcel is flagged; it adds $1,500–$3,000 and 2-3 weeks. Similarly, if your lot is in a flood zone (check the FEMA map and Tigard's flood overlay), you must elevate the ADU floor above the base flood elevation; this often means a raised foundation and significant site rework. Conversely, if you're on a hillside lot (over 15% slope in some areas), the city may require slope stability analysis. These geotechnical and drainage flags are identified in Tigard's pre-application or early planning phase; they're not deal-breakers, but they add cost and timeline.

The permit application and inspection sequence for Tigard ADUs is straightforward if you have complete plans. Submit a building permit application (online via Tigard's portal or in person) with site plan (showing setbacks, easements, utilities, and parking if any), architectural floor plans and elevations (drawn to scale, noting materials and fenestration), electrical, plumbing, and structural (if detached). The planning division reviews first (usually 10-15 business days) to confirm no zoning violations and that the ADU meets Tigard Code 18.86; building review follows. Plan-check comments are consolidated and returned once; typical turnaround is 10-15 business days if the application is complete, but incomplete applications bounce back immediately, costing 1-2 weeks. Once approved, inspections are standard: foundation inspection (before concrete pour or immediately after if already completed), framing inspection (before drywall), rough trades (electrical, plumbing, gas, HVAC rough), insulation, drywall, final building, final electrical, final plumbing, and final planning sign-off. For a detached ADU, expect 6-8 inspections over 12-16 weeks of construction. Tigard allows owner-builder for owner-occupied ADUs, but the owner must be listed as the principal residence occupant; if you plan to rent the ADU from day one, you must hire a licensed contractor (and disclose that to the city). If you're renting, also register the ADU as a rental unit with Tigard's Planning and Building Division within 30 days of occupancy; failure to register can result in a code violation.

Three Tigard accessory dwelling unit (adu) scenarios

Why Tigard's ADU rules are different from the rest of Oregon — and what that means for your timeline

Oregon state law (ORS 197.312, effective 2020) requires all cities to allow at least one ADU per single-family lot as a permitted use, but it sets a floor, not a ceiling. Some Oregon cities (Bend, Salem, Corvallis) have gone further and explicitly waived parking, owner-occupancy, and fee caps. Tigard is one of the most ADU-aggressive cities in the state. Tigard's municipal code (18.86, adopted 2021) allows multiple ADU types (detached, attached, junior, accessory to principal), waives parking entirely (no on-site parking required for the ADU), imposes no owner-occupancy mandate (you can rent an ADU from day one), and sets a fee cap at no more than 25% of the standard single-family residential permit fee. This is distinct from Portland, which allows ADUs but still imposes parking requirements in some zones and charges higher fees. It's also different from Lake Oswego and Beaverton, which have carved out ADU exceptions but retain more restrictive design guidelines.

The Tigard advantage shows up in two concrete ways: first, your approval timeline is predictable. The city publishes a pre-approved ADU checklist and design guidelines; if you follow them, your application sails through plan review in 10-15 business days. Contrast that with Portland (3-4 weeks, often multiple rounds of comments) or unincorporated Clackamas County (6-8 weeks, case-by-case review). Second, your soft costs are capped. Tigard's building permit for a detached ADU under 800 square feet is typically $900–$1,200; a plan review is $600–$800. Nearby Beaverton charges $1,800–$2,500 for the same work. Over the course of a project, this $600–$1,500 difference per permit compounds, especially if you need re-reviews or variance work.

The hidden catch is that Tigard still enforces full building code (2021 IBC/IRC) with no shortcuts or fast-track exceptions. You cannot use the California SB 9 pre-approved plan library or the pre-designed ADU templates that fast-track projects in San Jose or Sacramento. Tigard requires site-specific plans, engineering (if the lot is constrained), and full inspections. This is neither better nor worse than other Oregon cities — it's just the trade-off: you get fast permitting and low fees, but you still have to build to full code. If your lot has any complexity (slope, utilities, setbacks, drainage), that complexity gets reflected in plan-check time and inspection cycles, not in fee waivers.

Utilities, sub-metering, and the real cost of separating a detached ADU from the main house

The biggest surprise for Tigard ADU builders is utilities. Detached ADUs must have separate connections; this is not optional and is nearly always the costliest line item in the project. A separate water lateral from the main house service to the ADU (typically 50-150 feet, depending on lot depth) costs $6,000–$10,000; a separate sewer lateral is another $6,000–$12,000. Tigard Water & Wastewater Services requires a separate meter for the ADU (not a sub-meter off the main line) if it's detached, which means the city reads two meters instead of one. The water lateral must be buried at least 18 inches deep in the Willamette Valley (frost depth 12 inches; Tigard adds 6-inch safety margin) and follow easement paths shown in the utility plan submitted with your building permit. If your property has an existing storm drain easement or conflicts with an underground power line, the contractor must locate and clear those conflicts before trenching — add $500–$1,500 for locating and $1,000–$3,000 for rerouting.

Electrical is simpler but still a choice point. You can either run a separate 100-amp service to the ADU (cost: $4,000–$6,000, plus transformer and panel work at the main house) or install a sub-meter off the main service panel ($1,500–$2,500). Tigard allows sub-metering for detached ADUs as long as the sub-meter is installed by a licensed electrician and labeled per NEC 690.12 (current NEC). If the main house panel is full or aged (60-amp service), you may need to upgrade the main service first (add another $2,000–$4,000). Plumbing for the ADU includes water supply (sized per IPC Table 422.1, typically 3/4-inch copper or PEX), drain lines (per IPC Chapter 3, minimum 2-inch waste stack for a one-bathroom ADU), and a separate gas line if the ADU has a furnace or water heater. Gas line trenching runs $1,500–$3,000 depending on distance and soil conditions (alluvial soil in the Willamette Valley requires conduit, adding cost).

Pro tip: Tigard Planning requires a utility plan (scaled site drawing showing meter locations, lateral paths, easement clearances, and connection points) as part of the building permit application. Incomplete utility plans bounce the application back immediately. Before you finalize your ADU design, have your plumber and electrician walk the lot and mark out utility routes; build that into your site plan. This saves 1-2 weeks of back-and-forth. Also confirm with Tigard Water & Wastewater (phone 503-639-4171) that your lot has sufficient water pressure (typically 40-80 PSI) and that there's capacity in the main sewer line. Some areas of Tigard (especially near the industrial district) have aging sewer lines with known capacity constraints; if your area is flagged, the city may require onsite detention or require you to upgrade the lateral as a condition of approval. This is rare but crucial to know early.

Common questions