Estimate Desk
ADU cost estimate
Detached cottage, attached unit, or a garage conversion. Drawings and a permit allowance are lines, not footnotes. The band is a Kitsap planning range, about ±15%, not a contract price.
Default scenario
600 sf detached, standard finish, one bath, full kitchen
$309,000 – $418,000
ADUs, additions, and basement suites. Drawing and permit lines are called out, not buried.
Planning band
$309,000 – $418,000
About 63 working days on site. Not a bid.
Line items, notes and what is not in the band are below the form.
Planning bandLine items and notes
$309,000 – $418,000
Point total about $363,000 · about 63 working days on site
Material and labor of the unit-priced lines: Material $132,000 · Labor $132,000
Default scenario: 600 sf detached, standard finish, one bath, full kitchen. Not a contract price. The band is the point total plus or minus 15%, a planning allowance we set for early estimates, not a measured accuracy. Prices include materials, labor, JKM overhead and fee, and 9.3% Washington sales tax. Working days on site are crew days. Design, permits and material lead times add calendar time before and between them.
| Item | Qty | Total |
|---|---|---|
| ADU shell and finish | 600 sf | $264,000 |
| Site work allowance — trench, gravel, short walk | 1 ls | $23,000 |
| Utility connection allowance | 1 ls | $12,500 |
| Design and permit drawings | 1 ls | $12,800 |
| Permit fee allowance — jurisdiction sets the real fee | 1 ls | $4,600 |
| Full kitchen, not a kitchenette | 1 ls | $19,420 |
| Contingency (8%) | 1 ls | $26,906 |
Notes
- The per-square-foot rate is a Kitsap planning composite for a simple rectangle on a buildable lot. Steep sites, shoreline, and septic replacement sit outside it.
- Contingency is 8% and is inside the point total.
- Rent, taxes, and an owner-occupancy rule are not priced. Confirm the ADU rules for the city before design.
Not in this band
- Hazardous-material abatement. Asbestos and lead are common on pre-1978 houses and are separately licensed work.
- Structural repair discovered after demolition.
- A new electrical panel, water service, or septic, unless that line is on this estimate.
- Design fees, except where a drawing line is shown.
- Financing and temporary housing. (Washington sales tax, 9.3%, is included in these prices.)
- Septic design or replacement, shoreline permits, and impact fees beyond the allowance.
Planning band for Kitsap County. Not a bid. A site visit sets the number.
What the ADU estimate covers
The ADU estimate prices a detached cottage, an attached unit or a garage conversion from its floor area, finish level, kitchen and number of baths. It starts from a detached unit of modest size at standard finish with one bath and a full kitchen, and the area box accepts anything from a small studio to a large cottage.
Drawings and the permit fee are lines in the estimate, not footnotes. For a project that has to be designed, drawn and permitted before the first shovel goes in, that matters as much as the cost of the walls.
What moves the number
Type changes the starting point. A garage conversion works inside a shell that already exists, so the desk prices it lower per square foot than a detached cottage, and an attached unit sits between the two. Detached units also carry allowances for the trench, gravel and short walk to the site and for the utility connection, because a new building needs its own.
Finish level moves the rate, and a full kitchen or a second bath each add a line you can see. Size matters twice: it changes the construction line and it changes the allowance for drawings.
Contingency and the age of the building
The point total includes a contingency line, and it is larger when the unit is built into or onto a building from before 1978, where wiring, moisture and finishes tend to hold surprises. The percentages are on the how estimates work page and come from the same engine as this one.
What is not in the band
The per-square-foot rate is a planning composite for a simple rectangle on a buildable lot. Steep sites, shoreline and septic replacement sit outside it, along with the standard exclusions on every estimate: hazardous-material abatement, structural repair found after demolition, a new panel or water service unless shown, design fees beyond the drawing line, and financing and temporary housing. Washington sales tax is already included in the prices.
ADU rules, such as size, parking and owner-occupancy, are set by the city or county where the lot sits and they differ from one to the next. Read the rules for your address in our permit guides before you design, then ask for a site visit and we will turn the band into a written estimate.
Scope ladder
ADU: three scopes compared
Each row is the Estimate Desk engine run on the inputs listed, so these numbers move whenever the desk does. They are planning bands, about ±15%, not bids.
| Scope and what was priced | Planning band |
|---|---|
Garage conversionA unit built inside an existing garage shell at builder finish, with a kitchenette inside the rate and one bath.
| $199,000 – $269,000Point total about $234,000About 63 working days |
Detached cottageDesk defaultA new standalone unit at standard finish with a full kitchen and one bath, plus site work and a utility connection.
| $309,000 – $418,000Point total about $363,000About 63 working days |
Larger, higher finishA larger detached unit at premium finish with a full kitchen and a second bath.
| $479,000 – $649,000Point total about $564,000About 75 working days |
Questions
ADU estimates: common questions
What does the ADU estimate assume before I change anything?
The starting band, $309,000 – $418,000, is the default scenario (600 sf detached, standard finish, one bath, full kitchen). It includes the shell and finish, a site-work allowance, a utility connection allowance, design and permit drawings, a permit fee allowance, the full kitchen and a contingency inside the point total.
Why does an ADU estimate show drawings and permit fees as separate lines?
Because they are real costs that arrive before any construction does. The desk lists design and permit drawings and a permit fee allowance on their own lines, and the note under the fee says the jurisdiction sets the real number.
Does the ADU band include rent, taxes or owner-occupancy rules?
No. The estimate prices construction only. Rent, property taxes and any owner-occupancy requirement are not priced, and the rules differ by city and county, so confirm them for your lot before design begins.
What can push an ADU past the planning band?
A steep or hard-to-reach lot, shoreline rules, and septic design or replacement all sit outside the rate. Impact fees beyond the allowance do too. Each is something a site visit can check before you commit to drawings.
A site visit sets the number
Bring your result to the walk. We measure, check what is behind the walls, and replace the planning band with a written estimate.