Detached vs. Attached ADU: Which Is Right for Your Battle Ground Property?
Both get you an ADU. But the decision between detached and attached shapes the cost, the timeline, the permit process, and how the finished unit actually lives — for you and whoever ends up in it.
Here’s how to think through it for a Clark County property.
The Basic Difference
An attached ADU shares at least one wall with the main home. It could be a converted garage, a basement unit, or an addition built onto the side or back of the house. An detached ADU is a fully separate structure — its own foundation, its own walls, its own roof.
Both are legal in Clark County under Washington State’s ADU laws. Both require permits. The differences are in how they’re built, what they cost, and how they function once they’re done.
Attached ADUs: Pros and Cons
Lower cost in most cases
When an ADU shares a wall with the main home, you can often tap into existing HVAC, electrical panels, and sometimes plumbing. That reduces infrastructure cost. Attached ADUs in Clark County typically run $80,000–$160,000 for new construction.
Easier on smaller lots
If you’re on a typical Battle Ground residential lot without a lot of backyard depth, an attached addition or basement conversion may be the only option that fits within setback requirements.
Less privacy for both parties
Shared walls mean shared noise. If you’re housing a tenant (not family), this matters more than people expect. Sound insulation helps but doesn’t solve it entirely.
Fire separation requirements
Washington code requires a 1-hour fire separation between an ADU and the primary dwelling when they share a wall. That’s Type X drywall on both sides, fire-rated door assemblies, and careful detailing at penetrations. Adds cost and inspections.
Detached ADUs: Pros and Cons
More privacy, better for rental
A detached ADU feels like its own place because it is its own place. Separate entrance, no shared walls, no noise crossover. If rental income is the goal, detached units rent for more and have lower turnover.
Higher upfront cost
All utilities have to reach the structure independently. Water, sewer, electrical, and sometimes gas all need separate runs. In Clark County, detached ADUs typically run $120,000–$220,000+ for new construction, depending on size and site conditions.
Cleaner permit path in Clark County
Detached ADUs in Clark County don’t have the fire separation complexity of attached units. They do need their own full permit set, but the inspection points are often more straightforward. Shawn and the I See Construct team handle the permit coordination — that’s part of how we run every project.
Requires lot space
You need room. Clark County requires setbacks from property lines — typically 5 feet from the rear and side. The structure also can’t exceed a certain percentage of the lot coverage. If your lot is tight, this may eliminate the detached option.
What Most Battle Ground Homeowners Choose
Homeowners with existing underused garages usually go the conversion route — attached or detached depending on what they have. It’s lower cost than new construction and faster to permit.
Homeowners with larger rural or semi-rural lots in Clark County — Battle Ground has a lot of these — often prefer detached new construction. More privacy, better long-term rental potential, and the structure is purpose-built rather than adapted.
The Decision Usually Comes Down to These Three Questions
- Who’s living in it? Family members — especially parents or adult kids — tolerate proximity better than tenants. If rental income is the goal, detached is usually worth the extra cost.
- What’s on your lot? Lot size, setbacks, and what structures already exist narrow the options quickly. We look at this during the free consultation.
- What’s your budget? If you’re working with $90,000–$120,000, an attached conversion or addition is realistic. Detached new construction almost always runs higher.
I See Construct builds both. We’re based in Battle Ground and have been working in Clark County for over 30 years. Call (360) 989-0118 or visit iseeconstruct.com/adu-construction to talk through your property.