Services · ADU construction
ADU builders in Vancouver and Clark County
Backyard cottages, attached ADUs, garage and basement conversions: designed to Washington's new ADU rules, permitted and built by one accountable team.
- 1,000 SFVancouver ADU size cap
- 2 per lotADUs allowed under HB 1337
- FreeIn-home estimates
- WarrantyIn writing
Washington just made ADUs much easier
House Bill 1337 rewrote the rules for accessory dwelling units across Washington's urban growth areas: at least two ADUs allowed per lot, size caps no lower than 1,000 square feet, no owner-occupancy requirement for long-term rentals, limited parking mandates near transit, impact fees capped at half the principal unit's, and heights up to 24 feet. Clark County jurisdictions have been updating their codes to match. The practical effect: lots across Vancouver, Camas, Battle Ground, Ridgefield and the county's urban areas that could not host an ADU three years ago now can.
Local rules at a glance
- City of Vancouver: ADUs up to 1,000 square feet, two units per lot, no owner-occupancy requirement, and no requirement that the ADU match the main house's architecture. From July 31, 2026 the city allows more residential structures per lot, with up to two being ADUs.
- Clark County (urban, unincorporated): 1,000 square feet standard; 1,500 square feet on lots of 20,000 square feet or more; basement ADUs may use the full basement; two ADUs capped at 2,000 square feet combined.
- Parking: none required within a half-mile walk of major transit; otherwise at most one space on lots up to 6,000 square feet. Vancouver applications cannot remove the main home's required space.
What an ADU costs
| ADU type | Published range | Source |
|---|---|---|
| Detached new build, 400 to 800 sq ft | $140K to $300K ($350 to $400 per sq ft) | 2025 ADU cost guides (The House Plan Company) |
| Attached ADU | $120K to $250K ($300 to $350 per sq ft) | 2025 ADU cost guides (The House Plan Company) |
| Garage conversion | $80K to $175K ($250 to $300 per sq ft) | 2025 ADU cost guides (The House Plan Company) |
| Basement conversion | $75K to $220K ($190 to $250 per sq ft) | 2025 ADU cost guides (The House Plan Company) |
| Permits and utility connections | $5K to $25K additional | 2025 ADU cost guides (The House Plan Company) |
Where these numbers come from. We publish ranges from named guides instead of hiding pricing. Site work, utility routing and finish level swing ADU budgets more than almost any other project type, and Washington adds retail sales tax, 8.9 percent in the City of Vancouver, to the full contract. Our ADU cost guide covers the drivers in detail.
Permits and process
An ADU is a full dwelling in the eyes of plan review: structure, energy code, egress, kitchen and bath systems, and utility connections all get checked. In the city, the application runs through Vancouver's ePlans portal as a RES permit; in unincorporated Clark County it goes through CC LMS, with the electrical permit from Washington L&I. We design to the jurisdiction's checklist from day one so review goes smoothly; the full picture is in our permit guide and our ADU rules explainer.
ADU questions
What does an ADU cost to build?
Published 2025 ADU guides put a detached 400 to 800 square foot unit at roughly $140,000 to $300,000 ($350 to $400 per square foot), attached ADUs at $120,000 to $250,000, garage conversions at $80,000 to $175,000 and basement conversions at $75,000 to $220,000, with permits and utility connections adding $5,000 to $25,000. Our ADU cost guide explains the drivers; the written estimate is the real number.
How big can an ADU be in Vancouver, WA?
The City of Vancouver allows ADUs up to 1,000 square feet of gross floor area, and two units per lot. In unincorporated Clark County inside the urban growth area the cap is also 1,000 square feet, rising to 1,500 square feet on lots of 20,000 square feet or more, with two ADUs allowed up to 2,000 square feet combined.
Do I have to live on the property to rent an ADU?
No. Washington's HB 1337 bars cities inside urban growth areas from requiring owner-occupancy except for short-term-rental ADUs, and the City of Vancouver has dropped its owner-occupancy requirement.
What did Washington's HB 1337 change?
Inside urban growth areas, cities must allow at least two ADUs per lot, cannot cap size below 1,000 square feet, cannot require owner-occupancy for long-term rentals, cannot demand extra parking within a half mile of major transit, must limit impact fees to half of the principal unit's, and must allow ADUs up to 24 feet tall.
Does an ADU need parking?
Under HB 1337, no extra ADU parking can be required within a half-mile walk of a major transit stop, and at most one space elsewhere on smaller lots. In Vancouver, ADU applications also cannot eliminate the main home's required parking space. We confirm your lot's exact requirement during design.
Can you convert our garage or basement into an ADU?
Yes. Conversions are usually the least expensive path because the shell exists. Clark County allows basement ADUs to use the full basement area as long as the ADU does not exceed the primary dwelling's size. Egress, ceiling heights, insulation and separate systems are what plan review focuses on.
Free on-site estimates
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- Written pricing
- Permits handled
- Warranty in writing