Hillsboro, OR Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Hillsboro, OR, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Governing provision
- CDC § 12.40.100(C)(1)
- ADU cap
- One ADU per single detached dwelling/townhouse
- Floor area
- 250-750 sq ft, or up to 50% for level conversions
- Parking
- No added off-street parking required
- Reduced setback option
- 3 feet if 450 sq ft, single story
- Approval path
- CDC § 12.80.170 review required
Summary
Hillsboro allows homeowners to convert an existing garage into an accessory dwelling unit (ADU) under Community Development Code § 12.40.100(C)(1), one of three recognized ways to create an ADU alongside adding new floor area or building a detached unit. The converted space must meet the same occupancy, floor-area, parking, height and setback standards in Subsection D that apply to every ADU, and needs approval under § 12.80.170 before construction.
C.Creation of an ADU. An ADU may be created as follows:1.Converting existing floor area in an existing dwelling or accessory structure such as a garage;2.Adding new floor area to an existing dwelling or accessory structure; or3.Constructing a separate unit on a lot with a new or existing primary dwelling. ... 5.a.Except as provided in subparagraph c. below, an ADU shall be at least 250 square feet, but not more than 750 square feet in area. ... c.An ADU created by the conversion of a level or floor (e.g., basement, attic, or second story) of the primary dwelling may occupy the entire level or floor, even if the floor area of the ADU would be more than 750 square feet. The maximum size shall not exceed 50% of the total square footage of the primary dwelling.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Municipal Code: Supplement 1 | Community Development Code: Supplement 1).
Full Breakdown
' A garage conversion falls under the first method and must still meet Subsection D's standards. 3). 4). c carves out a converted-floor exception: an ADU created by converting an entire level such as a basement, attic or second story can exceed 750 square feet, up to a cap of 50% of the primary dwelling's total square footage. i exempts 'ADUs created by converting existing floor area' from that behind-the-plane rule, recognizing that an existing garage's location cannot be moved. c, side and rear setbacks can shrink to 3 feet. 8). 150.
Violations & Fines
An ADU, including one created by garage conversion, cannot be occupied without approval under Section 12.80.170 and compliance with building, fire, health and safety codes required by Subsection D.10. A garage converted to living space without that land-use approval and without a building permit is subject to the City's standard code-compliance and permitting enforcement, and occupancy or utility connections can be withheld by the Building Division until the ADU meets the Subsection D standards.
Frequently Asked Questions
Can I convert my garage into an ADU in Hillsboro?
How big can a converted-garage ADU be in Hillsboro?
Does a converted garage ADU need to sit behind the house like other ADUs?
Sources & Official References
Other rules in Hillsboro
Compare Hillsboro to another location·View the Oregon accessory structures overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.
Garage Conversions in Nearby Cities
How other cities in Washington County handle garage conversions.