ADU Permits in Vancouver, WA: Two Requirements That Surprise People

Even with permit experience, ADUs in Vancouver still throw curveballs. Here are two I ran into, plus how the City of Vancouver and Clark County rules differ.

1. The utility report comes first

The City of Vancouver requires a Request for Utility Services (sometimes called a PIR) before you can apply for a permit for any new dwelling unit, including an ADU. The city reviews water, sewer and stormwater and gives you a report. It's free, and it takes at least two weeks. I only learned about this recently, so build that time into your schedule. (official source)

2. Garage conversions still need a site plan

Even if you're converting a garage into an ADU internally and the footprint isn't changing at all, the city still requires a site plan. That caught me off guard, since there's no ground disturbance and no footprint change.

How Vancouver and Clark County ADU rules differ

• City of Vancouver: up to two ADUs per lot. A unit counts as an ADU only if it's 1,000 square feet or less. A bigger unit may still be allowed, but it isn't treated as an ADU and doesn't get the reduced impact fees. Attached, detached and conversion ADUs are all allowed. (official source)
• Clark County, urban: up to two ADUs per lot, each up to 1,000 square feet, with 2,000 square feet combined. On lots of at least 20,000 square feet, one ADU can be up to 1,500 square feet, so a 1,500 and 500 split works there. The county's urban ADU rules were updated in 2024 and amended again in 2025. (CCC 40.260.020: official source)
• Clark County, rural: one rural ADU per lot, and it must be attached to the house, meaning it shares a common wall. The 1,500 square foot limit is total floor area, including nonhabitable space but not counting garages. A basement rural ADU can use the whole basement if it has a separate exterior entrance, as long as it doesn't exceed the size of the main house (CCC 40.260.022(C)(6)(b)). The county lists four ways to create one: an internal conversion, an addition to the house or an attached garage, converting an existing attached garage, or building it as part of a new house. My understanding is that the county wants to keep people from building a detached ADU, subdividing the property and selling the ADU separately. (Clark County rural ADU page: official source)

Plan ahead

Build the utility report's two weeks into your schedule, have a site plan ready even for an interior conversion, and confirm which ADU rules apply to your lot. See: City of Vancouver, Clark County, ADU calculator.

My work covers the permit itself: I take the project through city or county approval and send out the approved plans. Once construction starts, each trade pulls its own permits, like mechanical, electrical and plumbing, and that part is outside my scope.

FAQ

Does an interior garage-to-ADU conversion need a site plan in Vancouver?

In my experience, yes, even with no footprint change.

How many ADUs can I build?

Up to two in the City of Vancouver and urban Clark County. Rural Clark County allows one, and it must be attached.

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