ADUs are allowed in HillsboroTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Hillsboro, OR
Is your property eligible for an ADU?
# of Properties
31,195
Owner-occupied
75%
Zoning districts
43
Avg Home Value
$587,713
Median Lot Size
0.14 acres
Avg Income
$121,181
Residential Types:
31,195 housing units
Apts (4+ units)
2%
Other
98%
Zoning Districts:
33,162 parcels · 43 districts
R-7
37%(12,382)
MR-1
14%(4,808)
R-6
8%(2,647)
SCR-MD
6%(1,879)
Other
35%(11,446)
ADU Rules
What can you build in Hillsboro, OR?
Hillsboro, OR follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: By Right
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum internal ADU size: 750 sq ft, measured excluding exterior walls, interior stairs, shared space, interior parking, and certain unfinished storage (not applicable if converting a full floor).
- –Alternate maximum for internal ADU created by converting an entire floor: up to 50% of the primary dwelling’s total floor area; ADU floor area measured excluding exterior walls, interior stairs, shared space, interior parking, and certain unfinished storage.
Detached ADU Size Limits
- –Maximum detached ADU size: 750 sq ft (floor area measured excluding exterior walls, interior stairs, common/shared space with primary, interior parking, and non-internally-accessible unfinished storage).
Max Units
- –1 ADU per single detached dwelling or townhouse
Owner Occupancy
- –No owner-occupancy requirement for ADUs
Parking
- –No off-street parking required; max 1 (Zone A) or 2 (Zone B); retain/replace required primary-dwelling spaces if converted
ADU State Law
What can you build in Oregon?
- –In urban growth areas, Oregon law requires cities and counties to allow at least one ADU on lots zoned for detached single-family homes.
- –Local jurisdictions cannot require owner occupancy for ADUs, but may regulate short-term or vacation rentals.
- –There are no statewide limits on ADU size, height, setbacks, lot size, or floor area ratio. Local zoning rules apply.
- –Parking requirements, if any, are set by the local jurisdiction, subject to state limitations.
- –Some cities may allow more than one ADU per lot, depending on local code.
- –Oregon law does not require counties to allow ADUs in rural residential zones. Whether an ADU is allowed depends on county zoning.
- –ADUs in rural residential areas cannot be used for short-term or vacation rentals.
- –Additional requirements may apply related to wildfire risk, water supply, septic capacity, and fire access.
- –Counties may impose additional restrictions beyond state law or choose not to allow ADUs at all.
- –If a county allows ADUs, state law imposes strict limits, including a minimum 2-acre lot size, a maximum ADU size of 900 sq ft, a location within 100 ft of the primary dwelling, and a limit of one ADU per parcel.
What's allowed on your lot?
These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.
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ADU rules in other Oregon municipalities
Rules change at the town line. Check the municipality your property is actually in.
Washington County