Where the money goes
An ADU budget has five parts. The building is the biggest, but utilities and site work are what surprise people.
- The building: foundation, framing, roof, windows, systems, finishes. Scales with square feet and finish level.
- Utilities: sewer or septic, water, power, and sometimes a new meter or panel upgrade.
- Site work: clearing, grading, excavation, drainage, access for equipment.
- Soft costs: site plan, permit and inspection fees, impact or connection fees, surveys or septic design.
- Plans: $0 for Kitsap pre-approved plans in eligible urban areas; a license fee for plans from other architects.
What we see per square foot
For the building itself, our ADU builds usually run $325 to $550 per square foot, depending mostly on finish level. That's the range we use for early budgets; your fixed price comes from a site visit and a line-item estimate.
| Plan | Size | Building at $325–$550 per SF |
|---|---|---|
| The Lille | 480 SF | $156,000 – $264,000 |
| The Sidney | 600 SF | $195,000 – $330,000 |
| The Sinclair | 800 SF | $260,000 – $440,000 |
| The Blakely | 800 SF | $260,000 – $440,000 |
| The Kitsap | 834 SF | $271,050 – $458,700 |
| The Salish | 1,000 SF | $325,000 – $550,000 |
Not included in that range: site work such as clearing, grading and excavation; utility connections; septic design and installation; and permit, impact and connection fees. Those depend on your lot, so we price them after we've seen it.
Permit fees are their own line. For the county plans in unincorporated Kitsap, the county publishes approximate building permit fees:
| Plan | Size | Approx. county permit fee |
|---|---|---|
| The Lille | 480 SF | $4,666.50 |
| The Sidney | 600 SF | $5,120.29 |
| The Sinclair | 800 SF | $5,847.15 |
| The Blakely | 800 SF | $5,770.24 |
| The Kitsap | 834 SF | $7,235.45 |
| The Salish | 1,000 SF | $6,593.72 |
What moves the number
- Distance to the sewer main and the house panel. Long trenches add up fast.
- Slope and soils. Steep lots need more foundation and excavation.
- Septic. Adding a bedroom on septic may mean a new or expanded system.
- Two stories vs. one. Two stories save foundation and roof per square foot but add stairs and structure.
- Finish level. Cabinets, flooring, fixtures and windows swing the per-square-foot cost the most.
Ways to keep it down
- Use a county pre-approved plan as drawn: no design fee and less review.
- Place the ADU close to existing sewer and power.
- Pick the smallest plan that meets the need; each square foot carries cost.
- Decide finishes before the bid so the price doesn't move later.
How people pay for it
Common routes are cash, a home equity line of credit, a cash-out refinance, or a construction or renovation loan. Lenders differ on how they treat future ADU rent. This isn't financial advice; talk to a lender about your situation.