Residential drafting in Hillsboro, Oregon
Hillsboro spans two very different project environments. The downtown grid and the historic Orenco district hold older houses, some with alleys and rear access. South Hillsboro is recent planned community development on smaller, tightly designed lots with private design standards.
Orenco is distinctive because it began as a company town rather than as a streetcar suburb, and exterior work there can run into historic review that would not apply a mile away.
Between those two, the city holds a large body of postwar ranch housing where garage conversions and rear additions are the common requests.
Floodplain and significant natural resource overlays affect parts of the city, and Clean Water Services regulates stormwater across the area, so new impervious surface has to be accounted for on the drawings rather than assumed.
ADU standards
Setback, size, and parking rules for an accessory dwelling unit in Hillsboro.
| Size range | At least 250 sq ft and no more than 750 sq ft (12.40.100.D.5) |
|---|---|
| Whole level conversion | An entire existing floor may exceed 750 sq ft, but the unit may not exceed 50 percent of the house's total square footage (12.40.100.D.5.c) |
| Setbacks | The zone or plan district standard (12.40.100.D.7.a) |
| Reduced setback | 3 ft side and rear, only at 450 sq ft or less, one story, 10 ft tall or under, with eaves 2 ft off the line and 6 ft of separation from every other structure (12.40.100.D.7.c) |
| Placement | Behind the front building plane of the house, except for a conversion (12.40.100.D.7.b) |
| How many | One per legal single detached dwelling or townhouse (12.40.100.D.2) |
| Parking | None required for the unit, but parking required for the house must be retained or replaced (12.40.100.D.4) |
| Entrance | May face any direction, but needs a recess or porch at least 2 ft deep and 5 ft wide, with lighting and glazing (12.40.100.D.8) |
| Privacy glazing | On an elevation facing and within 20 ft of a neighboring residential property, glazing goes in the upper third of each story unless a 6 ft screen is installed (12.40.100.D) |
| Review | Zoning Review approval is required before the building permit can issue (12.70.025, 12.80.170) |
Hillsboro has the tightest size range in this metro: no smaller than 250 square feet and no larger than 750 (12.40.100.D.5). Converting a whole existing floor can exceed that, but the unit still cannot exceed half the house's square footage.
The three foot reduced setback exists but almost nothing qualifies for it. The building has to be 450 square feet or less, one story, no taller than 10 feet measured at the midpoint between peak and eave, with eaves at least two feet off the line and six feet of separation from every other structure (12.40.100.D.7.c). Add a breezeway to the house and the unit counts as attached, which disqualifies it. Most real projects take the district setbacks.
The design standards here are more prescriptive than anywhere else in our Oregon coverage. The entrance needs a recess or porch at least two feet deep and five feet wide, with lighting and glazing. Every facade needs at least two articulation elements. And on any elevation facing a neighboring residential property within 20 feet, the glazing has to sit in the upper third of each story unless a six foot screen or evergreen planting goes in (12.40.100.D.8, D.9).
Hillsboro also requires Zoning Review approval. The building permit cannot be submitted before the zoning application is in, and it cannot issue before that approval lands (12.70.025). The two can run concurrently.
Planning office: Hillsboro Development and Permit Center
Sources: Hillsboro Community Development Code 12.40.100. Ordinance 6508, adopted November 2025. Hillsboro Community Development Code 12.70.025, 12.80.170. ORS 197A.425. Last checked August 2026.
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