If you have been thinking about adding more living space to your property, an Accessory Dwelling Unit (ADU) can be one of the most flexible and affordable paths. ADUs are growing in popularity across Southwest Washington, and Cowlitz County is no exception. Homeowners are using ADUs to create rental income, support multigenerational living, or add long term value to their property.
The challenge is that ADU zoning and permitting rules in Cowlitz County can feel confusing if you have never gone through the process before. This guide breaks everything down in a simple and easy way so you can understand exactly what the county requires before starting your project.
If you want to know whether your property qualifies for an ADU, start with Wolf’s free property evaluation. It is the fastest way to understand zoning, setbacks, and feasibility before you invest time or money.
What Counts as an ADU in Cowlitz County
Cowlitz County defines an Accessory Dwelling Unit as a complete, independent living space located on the same lot as a primary residence. It must include permanent provisions for living, sleeping, cooking, and sanitation.
Both attached and detached ADUs are allowed as long as they follow specific requirements. Detached ADUs are often the simplest for homeowners because they provide more privacy and flexibility in design.
Where ADUs Are Allowed
Most residential zones in Cowlitz County allow ADUs as long as the parcel already contains a single family home. However, every property is different. Parcel size, zoning designation, and environmental overlays can all change what is possible.
Wolf verifies zoning for you during the property evaluation step and maps out the best placement on your lot. This saves weeks of uncertainty and helps you avoid costly redesigns.
Start your property evaluation here:
https://wolfind.com/contact/property-evaluation/
Size Limits for ADUs in Cowlitz County
ADUs in Cowlitz County must stay within the maximum size allowed by ordinance. The county uses the following guidelines:
• A detached ADU cannot exceed the maximum square footage set by code.
• The ADU must remain accessory to the primary home.
• Only one ADU is allowed per lot.
Attached ADUs have slightly different rules that apply when the ADU shares a wall with the main home.
Setbacks and Height Restrictions
Every ADU must meet the setback requirements of the underlying zoning district. This includes side yard setbacks, rear yard setbacks, and distance from other structures.
Cowlitz County also enforces height limits for detached ADUs to ensure they remain secondary to the main dwelling.
Wolf prepares a full site plan that accounts for setbacks, access, utilities, and final placement. This avoids surprises once you enter the permitting phase.
Owner Occupancy Rules
Cowlitz County requires an owner occupancy covenant for ADUs. The owner must live either in the primary residence or in the ADU. This requirement is recorded with the county and ensures the property is used for long term housing rather than short term rentals.
If you have questions about how owner occupancy works, Wolf walks you through every step.
Parking Requirements
Most ADU projects require at least one additional off street parking space on the property. Driveway layout, slope, and road access can affect what works best.
As part of the evaluation process, Wolf prepares a parking strategy that meets county standards and fits naturally with your site layout.
Utilities and Infrastructure
ADUs must be connected to approved water and sewer service or to a septic system that has capacity for the additional living space. Septic systems often require a review by the health department to confirm capacity.
Electrical service, driveway access, and emergency addressing also follow county guidelines.
Wolf handles all utility coordination during the permitting and sitework planning stages so you do not have to manage multiple agencies on your own.
Design Standards and Exterior Appearance
Some ADU types must follow design consistency rules. This can include exterior siding, roof pitch, trim, or colors that are compatible with the primary home.
Wolf homes already meet or exceed common ADU design requirements, and our Options Book gives you full control over finishes that fit your property.
Permitting Requirements in Cowlitz County
To build an ADU in Cowlitz County, homeowners typically need:
• A completed ADU Supplement (county provided form)
• A building permit
• A planning review
• A site plan that shows placement, setbacks, and access
• Health department review if septic is involved
Permitting timelines vary based on project scope and county workload. Wolf manages the entire permitting process from start to finish, which removes a major source of stress for homeowners.
Common Mistakes Homeowners Make When Trying to Build an ADU
Many people run into delays for reasons that are completely avoidable, including:
• Starting design work before confirming zoning
• Misunderstanding setback requirements
• Assuming their septic system has enough capacity
• Submitting incomplete site plans
• Not accounting for required parking
• Underestimating sitework needs such as trenching, foundation, and utilities
Wolf’s turnkey ADU process prevents these issues and keeps your project moving forward without costly restarts.
Why More Homeowners Choose Wolf for ADUs in Cowlitz County
Wolf offers a simpler and more predictable ADU experience for Southwest Washington homeowners. Our approach is built around:
• Local zoning and permitting expertise
• Predictable pricing that reduces financial uncertainty
• Fast factory construction that avoids weather delays
• Complete sitework and installation support
• Dozens of ADUs built throughout the region
• A streamlined process from evaluation to delivery
When you work with Wolf, you get a team that has already navigated Cowlitz County’s rules many times and knows how to move your project forward efficiently.
Start with a Free Property Evaluation
Understanding Cowlitz County WA ADU rules and regulations is the first step. The next step is finding out what your specific property can support.
Wolf makes this easy with a free property evaluation where our team reviews zoning, setbacks, utilities, driveway access, and suitability for one of our modular ADU models.
Start your evaluation here:
https://wolfind.com/contact/property-evaluation/