If you are thinking about adding an ADU in Skagit County, you are probably asking the real question first: Can I actually do this on my lot, and what will the County require before I spend a dime on plans?
That is the right instinct. ADU rules in Washington are changing fast, and Skagit County has also been actively updating its planning framework and development regulations as part of its periodic Comprehensive Plan update work.
If you want to skip the guessing, start with Wolf’s free property evaluation. Submit your address and we will help you confirm feasibility, surface the likely constraints early (zoning, site layout, utilities, setbacks, critical areas), and map the cleanest path forward.
What is an ADU in Skagit County?
Skagit County defines an accessory dwelling unit (ADU) as a separate living quarters on the same lot that is either within the primary residence or detached, typically including living essentials like kitchen and bathroom facilities. Skagit County’s definition also makes clear that mobile and manufactured homes and recreational vehicles cannot be used as an ADU, and that ADUs are subject to the County’s development requirements.
This matters because many homeowners start with an idea like “We will just put a trailer in the back.” That is not how Skagit County defines a compliant ADU.
Skagit County ADU rules: the requirements you should expect
Skagit County’s development code materials and update documents highlight several core themes that typically govern whether an ADU will be approved: size, parking, location, life-safety separation, and, in many cases, how Urban Growth Area rules differ from rural areas.
Size limits
Older Skagit County code language (still widely circulated in County code PDFs and staff materials) has historically limited ADUs to a maximum of 900 square feet, and also tied size to the primary home’s square footage.
At the same time, Skagit County’s more recent Title 14 reorganization draft (part of the County’s broader code update work) shows an ADU framework that allows a newly constructed ADU up to 1,200 square feet.
What you should do with that information: treat ADU size as a site-specific confirmation item, not an assumption. The safest move is to verify the current size standard that applies to your exact location and zoning designation.
Get certainty before you design
Wolf’s free property evaluation helps confirm what size limits and site constraints are most likely to apply to your property before you invest in plans.
Parking
Skagit County code materials commonly state that three off-street parking spaces must be provided for the combined primary residence plus ADU.
Parking is one of the most frequent “surprise” issues because it seems simple until you account for driveway geometry, required maneuvering, and how existing site features affect what is realistically buildable.
Location and building code requirements
Skagit County allows an ADU to be attached, within, or in a detached structure, with fire separation requirements governed by applicable building standards.
County materials also emphasize that an ADU must function as a real dwelling, meaning it needs provisions for eating, sleeping, cooking, and sanitation, and that an internal ADU generally cannot have interconnected interior spaces with the primary unit.
Use limitations you cannot “design around”
Skagit County’s ADU definition and code materials prohibit using recreational vehicles (and similar temporary units) as ADUs.
Urban Growth Areas: where state law changes the conversation
Washington State’s ADU law (as summarized by the Washington State Department of Commerce) requires fully planning cities and counties to allow two ADUs on residential lots that allow single-family homes within an urban growth area, with specific standards such as:
- Allow two ADUs per lot (attached, detached, or combinations)
- Allow an ADU of at least 1,000 square feet
- No owner-occupancy requirement (except in limited short-term rental contexts)
- Allow sale as independent units
- Parking rules tied to transit proximity and lot characteristics
- Plus other limitations and implementation details
Washington State Department of Commerce also notes that if a jurisdiction does not meet its periodic update deadline, conflicting rules can be preempted by state statute.
Skagit County’s periodic update materials discuss allowing two ADUs in UGAs in certain infrastructure contexts, and the County’s code reorganization draft describes an ADU section that allows two ADUs in UGAs and requires public sewer for two ADUs.
Practical takeaway: if your property is in a Skagit County UGA, your ADU options may be meaningfully different than a rural property, especially if sewer availability is part of the County’s standard for two ADUs.
The permitting reality in Skagit County
Most homeowners do not get stuck because they do not want an ADU enough. They get stuck because they start spending money before they have answers to four gating items:
Zoning and allowed use
An ADU is usually treated as an accessory residential use tied to a primary dwelling. The key is verifying that your zoning allows the primary residential use and the accessory use as configured on your lot.
Utilities: sewer or septic and water feasibility
Utility feasibility is often the difference between “this is straightforward” and “this is a redesign.”
Critical areas and site constraints
Critical areas and flood-related constraints can change your buildable envelope dramatically, even when the zoning seems to allow an ADU conceptually.
Parking and site access
Even when a rule is simple on paper, some lots just do not physically support compliant parking and access without tradeoffs.
Let Wolf help you de-risk the first step
Submit Wolf’s free property evaluation form and we will help you identify the likely gating items before you commit to design costs.
Common homeowner questions about ADU rules in Skagit County
Can I build a detached ADU?
County code materials describe ADUs as allowed either within the primary home or in a detached structure, as long as requirements are met.
Can I put an RV or park model in the backyard and call it an ADU?
Skagit County’s definition and code materials prohibit recreational vehicles (and similar units) as ADUs.
Do I have to live on the property?
Historically, older Skagit County code language required owner occupancy supported by an affidavit and recording requirements. Separately, Washington State law generally prohibits owner-occupancy mandates for ADUs within UGAs, with limited exceptions. Because these standards can depend on location, the safest approach is to verify how your site is regulated today.
How many ADUs can I build?
In UGAs, Washington State law requires allowing two ADUs on qualifying lots, with limitations. Skagit County’s periodic update materials and draft code reorganization also describe a framework for two ADUs in UGAs, with an emphasis on sewer availability.
The fastest path to “yes” is getting the right answers first
If you want to build an ADU in Skagit County, the win is not finding an online checklist. The win is getting site-specific clarity before you spend money.
Wolf’s process is built around reducing uncertainty early: confirm feasibility, confirm constraints, then move forward with a plan that is designed to pass review and get built cleanly.
Start here: Wolf’s free property evaluation
Complete the form and we will help you understand what is realistic on your lot, what the likely permitting path looks like, and which Wolf home options best match your goals.
Sources
Skagit County Code, Title 14, Chapter 14.04 (Definitions)
https://skagitcounty.net/PlanningAndPermit/Documents/GMAupdate021006/Development%20Regulations/Amendments%20by%20Chapter/14.04.pdf
Skagit County Code, Title 14, Chapter 14.16 (Accessory Dwelling Units and related standards)
https://skagitcounty.net/PlanningAndPermit/Documents/GMAupdate021006/Development%20Regulations/Amendments%20by%20Chapter/14.16.pdf
Skagit County, “Exhibit A: SCC Title 14 Reorganization Draft for Public Release” (updated 4/21/2025)
https://www.skagitcounty.net/PlanningAndPermit/Documents/LongRangePlanning/PeriodicUpdate2025/Title14ReorgDraft_PUBLICRELEASE_04212025.pdf
Skagit County, SEPA DNS for 2025 Periodic Comprehensive Plan update (published 5/15/2025)
https://www.skagitcounty.net/PlanningAndPermit/Documents/LongRangePlanning/PeriodicUpdate2025/SEPA_DNS_PeriodicUpdate_2025_05152025.pdf
Washington State Department of Commerce, Accessory Dwelling Units (ADUs) guidance
https://www.commerce.wa.gov/growth-management/housing-planning/adus/
Skagit County Planning and Development Services (reference page)
https://www.skagitcounty.net/Departments/PlanningAndPermit/
GoSkagit: “Skagit County adopts new rules for ADUs, makes other policy changes”
https://www.goskagit.com/news/local_news/skagit-county-adopts-new-rules-for-adus-makes-other-policy-changes/article_8ea4983c-71e2-59aa-9fae-27f4732c0c3b.html