5 county-level rules, plus city-specific rules for 1 city in Marion County, Oregon.
Verified from official government sources
Oregon law requires Marion County and its cities to allow at least one accessory dwelling unit (ADU) for each detached single-family home in urban-growth-boundary residential zones, subject only to reasonable siting and design rules. Owner-occupancy and extra off-street parking cannot be required.
ORS 197.312(5)(a)
A city with a population greater than 2,500 or a county with a population greater than 15,000 shall allow in areas within the urban growth boundary that are zoned for detached single-family dwellings the development of at least one accessory dwelling unit for each detached single-family dwelling, subject to reasonable local regulations relating to siting and design.
In Marion County's rural residential zones, all accessory structures, including sheds, may cover no more than 25 percent of the rear yard. A shed's peak height is capped at nine feet at the lot line, rising with distance from the line.
MCC 17.117.020, 17.117.030
The lot coverage by all accessory structures, except fences in connection with uses in RS zones, shall not be more than 25 percent of rear yard area. The maximum peak height of any residential accessory structure shall be nine feet at the lot line.
In Marion County, an attached garage converted to living space is treated as part of the dwelling and must meet the same zoning and building-code standards. A detached garage turned into a living unit is regulated as an ADU or separate dwelling.
MCC 17.117.070
Covered or enclosed accessory buildings which are attached to the dwelling shall be considered as a portion of the dwelling and shall observe the same requirements as the dwelling. Accessory structures shall be considered as being attached to the dwelling when any portion of the accessory structure is located within five feet of the dwelling.
A carport is a residential accessory structure in Marion County. Its peak height is nine feet at the lot line, increasing with setback to 35 feet, and it counts toward the 25 percent rear-yard accessory-coverage cap under the Rural Zoning Code.
MCC 17.117.030
The maximum peak height of any residential accessory structure shall be nine feet at the lot line. Such maximum height may be increased one foot for each one foot of distance from the lot line to a maximum height of 35 feet. Roof drainage shall be accommodated within the confines of the property.
Marion County has no tiny-home-specific ordinance. A permanent tiny house on a foundation is regulated as a dwelling or accessory dwelling unit under state law and county zoning; a tiny house on wheels is generally treated as a recreational vehicle.
ORS 197.312(5)(b)(A)
“Accessory dwelling unit” means an interior, attached or detached residential structure that is used in connection with or that is accessory to a single-family dwelling.
1 cities in Marion County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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