Two quotes, two different scopes
A factory-built ADU is priced as a unit: the building, delivered. A turn-key price covers the building and the ground it lands on. Both can be honest numbers. They are not comparable numbers, and the gap between them is the site work.
Read the exclusions before the price
Whatever the quote is for, the exclusions page is where the real scope sits. The lines worth finding:
- Septic. Adding bedrooms can mean the existing system needs more capacity, or a new one. Is that capacity check in the price, or added after the design is done?
- Pumping. If the unit sits below the existing system, the waste has to be lifted. A pump station is a design decision, not a surprise, as long as somebody looked.
- Water. Flow and capacity on an existing well get tested, or they get discovered.
- Clearing, stumps and ledge. "Priced on site evaluation" means priced after the contract is signed.
- Getting the building in. A crane, a widened approach and a drive that will carry the load are real line items on a delivered unit.
- Utilities. The trench from the house to the new unit is as long as it is, and somebody has to dig it.
If the answer to any of those is an allowance, you have an estimate for part of the job, not a price for the job.
Questions that sort it out quickly
1. Is the septic work, including any expansion of the existing system, inside this number? 2. Who does the excavation and the site work, and when are they looked at? 3. What happens to the price if the test pit comes back tight, or the dig finds ledge? 4. Is clearing and stump removal in the scope, or evaluated later? 5. What has to be true about the lot for this price to hold?
How it works here
The site work and the building sit on the same contract. The lot is walked before the quote, so the clearing, the septic and the trenching are priced against what is on the ground rather than against a flat hypothetical lot. The catalog runs $147,000–$388,000 across ten published models, and the schedule is set out in what an ADU build actually looks like.
Setbacks, septic and shoreland still apply whichever way the unit is built. The rules in both states are in the ADU law update.
Start with the lot
Book a land review if the question is whether the parcel will take a unit at all, or a build scope if it already will.
The 2-minute calculator is on instant pricing. Published packages are on the ADU models.