Tigard, OR Accessory Structures: ADU Rules (2026)

Tigard Community Development Code (CDC) Chapter 18.220 governs accessory dwelling units. Under CDC 18.220, a maximum of one detached ADU is allowed per lot, and the total maximum number of dwelling units on a small form residential lot is three including the units in the small form residential development; detached ADUs are prohibited on lots already developed with three small form residential dwelling units. The maximum size of a detached ADU is 800 square feet, and the maximum height is 25 feet. Detached ADUs must meet the setback standards for small form residential development in the applicable base zone, with limited exceptions provided in CDC Chapter 18.220, and must comply with the lot-coverage standards for small form residential development under CDC Chapter 18.290 (Small Form Residential). Window and street-facing facade standards for small form residential development under CDC Chapter 18.290 also apply, so that an ADU facing the street meets minimum window-area thresholds. Detached ADUs may be added to or created from existing accessory structures such as detached garages, but the maximum 800-square-foot size cap applies to the entire structure, including any portion that remains in non-ADU accessory use. Attached ADUs are treated as small form residential development for purposes of meeting state law and the City's clear-and-objective standards under CDC Chapter 18.290. Consistent with Oregon SB 1051 (2017) and HB 2001 (2019), Tigard does not impose an owner-occupancy requirement and does not require additional off-street parking solely because an ADU is added. Building, plumbing, mechanical, and electrical permits follow the Oregon Residential Specialty Code adopted under ORS 455.020 and are issued by the Tigard Building Division. System Development Charges (SDCs) apply but were reduced in Tigard for ADUs as part of the 2018 housing-options package.