Accessory Structures in Cowlitz County, WA (2026)
2 rules for unincorporated Cowlitz County, Washington.
Verified from official government sources
ADU Rules
CCC § 18.10.585 lets unincorporated Cowlitz County property owners build one ADU, up to 1,200 square feet and 35 feet tall, on a lot at least 6,000 square feet, in any zoned area except MH, ML, C-1 and C-2. A building permit is required.
Cowlitz County Accessory Dwelling Unit Rules
Some RestrictionsCowlitz County Code § 18.10.585
§ 18.10.585. Accessory dwelling units. The county promotes development of accessory dwelling units as a means of enhancing and creating opportunities for individual property owners to provide housing options for families and generate rental income. ... 1. ... Where Permitted. An accessory dwelling unit (ADU) may be allowed in all Comprehensive Plan designations, and in all zoned areas except fo...
Shed & Carport Rules
A detached storage shed or playhouse in unincorporated Cowlitz County does not need a building permit if it is one story and no larger than 120 square feet, or 200 square feet when accessory to a one- or two-family home, under Cowlitz County Code § 16.05.090, and it must still sit at least 5 feet from the rear lot line under § 18.10.514.
Shed Size and Setback Rules in Cowlitz County
Some RestrictionsCowlitz County Code §§ 16.05.090, 18.10.514
Section 106.3, Work exempt from permit, is revised as follows: 1. One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided the floor area does not exceed 120 square feet (200 square feet if accessory to a one and two-family dwelling). ... The rear yard setback for any detached residential accessory structure shall be a minimum of five feet fr...
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