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Clark County, WA Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified July 2026

ADU rules in Clark County, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Urban ADUs per lot: Up to two (CCC 40.260.020)
Max size: 1,000 sq ft (1,500 on 20k lots)
Parking required (urban): None
Rural ADUs (RADU): One per lot, 1,500 sq ft max
Impact fee reduction: 75% off multifamily rate

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Washington under recent ADU streamlining laws. The Clark County, WA rules below cover local size, height, and setback requirements.

Summary

In the urban growth area you may build up to two accessory dwelling units per legal lot, each capped at 1,000 sq ft (up to 1,500 sq ft on lots of 20,000+ sq ft). Rural zones (RADU) allow one, capped at 1,500 sq ft. No parking is required for urban

These county ordinances apply to unincorporated areas of Clark County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

Up to two (2) ADUs per legal lot are permitted and they must be accessory to a single-family detached dwelling... The total gross floor area of an ADU shall not exceed one thousand (1,000) square feet... On lots that are at least twenty thousand (20,000) square feet, the maximum square footage of an ADU may be increased up to one thousand five hundred (1,500) square feet.

View official code

Full Breakdown

Clark County Code 40.260.020 governs urban ADUs: up to two per lot accessory to a single-family dwelling, via internal conversion, addition, garage conversion, or one/two detached structures. Each must meet the zone's lot coverage, setback, and height standards, connect to public sewer and water, and be at least 150 sq ft. Rural ADUs (RADU) under CCC 40.260.022 are limited to one per lot, must comply with fire/health/safety codes, provide one on-site parking space, and cap at 1,500 sq ft. Both receive a 75% reduction in school and transportation impact fees. City ADU rules differ inside Vancouver, Camas, etc.

Violations & Fines

Building an ADU without permits or exceeding size/setback standards is a code violation subject to stop-work orders, permit denial, and Title 32 nuisance/civil enforcement by Clark County Community Development.

Frequently Asked Questions

Can I build a detached ADU in the city part of Clark County?

In the urban growth area, county code allows one or two detached ADUs per lot. Rural zones allow only attached/internal RADUs, not detached ones.

Do I need extra parking for an ADU?

No parking is required for an urban ADU under CCC 40.260.020(C)(5). A rural RADU requires one on-site parking space.

Sources & Official References

Other rules in Clark County

Animal Ordinances: Chickens & LivestockSome Restrictions Shed & Carport RulesSome Restrictions Garage ConversionsSome Restrictions Tiny HomesSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions Fence Regulations: Retaining WallsSome Restrictions Animal Ordinances: Wildlife FeedingSome Restrictions Animal Ordinances: Cat RulesSome Restrictions Animal Ordinances: Pet LimitsSome Restrictions

All Clark County rules

How Clark County compares: Easiest Cities to Build an ADU·Compare Clark County to another location·View the Washington accessory structures overview

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ADU Rules in Cities Across Clark County

Vancouver, WA