ADU Rules & Permit Requirements in Washington State
Washington State made ADUs easier to build in 2021. The state passed legislation that pre-empted local restrictions that were blocking ADU development — things like owner-occupancy requirements, excessive parking minimums, and design standards that made ADUs impractical.
That said, local jurisdictions still control setbacks, lot coverage, height limits, and the permit process. Here’s what the rules look like specifically for Clark County and Battle Ground.
Washington State ADU Law (2021)
Under RCW 36.70A, cities and counties in Washington must allow at least one ADU per single-family lot. Key provisions:
- No owner-occupancy requirement. Washington counties can’t require you to live on the property to have an ADU. Clark County removed this requirement.
- No extra parking required. You can’t be required to add off-street parking solely for the ADU.
- ADUs must be allowed outright in residential zones. Local jurisdictions can’t zone ADUs out of single-family areas.
- Impact fees are limited. Clark County can charge impact fees for ADUs but they must be proportional to ADU size — not the same as a full single-family home.
Clark County ADU Standards
Clark County’s ADU rules are governed by Title 40 of the Clark County Code. The key numbers:
- Minimum ADU size: 200 square feet
- Maximum ADU size: Generally 1,000 square feet or 50% of the primary dwelling’s square footage, whichever is less
- Maximum height: Typically 25 feet for detached ADUs, though this varies by zone
- Setbacks: Usually 5 feet from rear and side property lines for detached ADUs; verify for your specific parcel
- Lot coverage: ADU square footage counts toward your lot’s total allowable coverage
- Number of ADUs: One ADU per residential lot is currently the standard in unincorporated Clark County
City of Battle Ground ADU Rules
Battle Ground is incorporated within Clark County and has its own municipal code. The city generally follows state ADU requirements but verify current standards with the city’s planning department or with us before drawing plans. We work in Battle Ground regularly and stay current on local requirements.
Permits Required for an ADU in Clark County
Every ADU build requires permits. There’s no legitimate path around this. Required permits typically include:
- Building permit. Covers structural, framing, insulation, energy compliance. This is the primary permit.
- Plumbing permit. Required for all plumbing rough-in and fixture installation.
- Electrical permit. Required for all wiring and panel work.
- Mechanical permit. Required for HVAC installation.
- Site development permit. May be required if grading, drainage, or significant site work is involved.
Clark County Community Development processes ADU permits. As of 2025, complete ADU applications typically take 8–16 weeks for permit issuance. An incomplete or incorrect application will extend that timeline.
What an Unpermitted ADU Costs You
An unpermitted ADU is a liability, not an asset. The real consequences:
- You can’t legally rent it. Renting an unpermitted unit exposes you to fines and potential civil liability.
- It doesn’t count toward property value. Appraisers and lenders don’t give credit for unpermitted square footage.
- You may have to tear it out. If discovered during a sale or complaint investigation, Clark County can require removal or retroactive permitting — often at significant cost.
I See Construct includes permit handling in every project. We pull the permits, manage the submittals, schedule inspections, and make sure the final Certificate of Occupancy is in your hands before we close out.
A Note on HOAs
Washington State law does not pre-empt HOA restrictions on ADUs. If your property is in an HOA, review the CC&Rs before proceeding. Most rural and semi-rural Battle Ground properties aren’t in active HOAs — but it’s worth confirming.
Questions About Your Specific Property?
ADU rules depend on your exact parcel — zone, lot size, existing coverage, setbacks. The fastest way to get a real answer is to talk to someone who knows Clark County’s code and has built here before.
I See Construct is based in Battle Ground and has been building in Clark County for over 30 years. Call (360) 989-0118 or visit iseeconstruct.com/adu-construction for a free consultation.