What a complete Seattle ADU bid should include
You get three to five bids for the same backyard cottage and they range from $80K to $550K. The low bid almost never wins because it's efficient — it wins because it left things out. This is the complete line-item list. Lay every bid against it, and the cheap one's hidden gaps show up fast.
Here’s the situation almost every Seattle homeowner hits. One homeowner described getting quotes that were “x, 2x and some 4x” for the same project (Facebook ADU group). Another posted bids “some quoted over $200,000, while others were around $100,000” for one garage-to-DADU conversion (r/Seattle). The fear underneath it is real: “I’ll get halfway through and discover the real number is double.”
The low bid almost never wins because it’s efficient. It wins because it left things out. Geotech, utility connections, sales tax, contingency — they don’t vanish. They come back as change orders after you’ve signed. The only defense is knowing exactly what a complete bid contains, so you can compare honestly and see what the cheap one is hiding. The bid that names all of these is usually the cheaper one by the time you get the keys.
The 11 categories a complete Seattle ADU bid must contain
| Line item | What it covers | Why low bids skip it |
|---|---|---|
| 1. Design / architecture | Floor plans, elevations, engineering, structural calcs | “We'll figure it out later” — design fees show up later as a separate invoice |
| 2. Survey | Property boundary + topographic survey | Assumed “not needed” until setbacks fail review |
| 3. Geotechnical | Soils report; required on slopes / ECA overlays | Skipped until the slope triggers a redesign mid-permit |
| 4. Permits + fees | SDCI or DPER permit fees, plan review, school/impact fees | Quoted as “TBD” — then billed at cost with markup |
| 5. Utility connections | Sewer tie-in, water meter, separate electrical, SPU/SCL | The single biggest surprise: $15K–$40K left as a blank line |
| 6. Sitework | Excavation, grading, drainage, erosion control, demo | Folded into a vague “site prep” lump |
| 7. Foundation | Footings, slab or crawlspace, waterproofing | Underscoped on sloped or wet lots |
| 8. Build (shell + systems) | Framing, roof, windows, plumbing, electrical, HVAC, insulation, drywall | The part everyone quotes — but to what energy-code spec? |
| 9. Finishes / allowances | Flooring, cabinets, fixtures, appliances, paint | Lowballed allowances that blow up at selection time |
| 10. Contingency | A stated reserve (typically 10–15%) for the unknown | Omitted entirely, so every surprise becomes a change order |
| 11. Washington sales tax | Sales tax on the contract (WA taxes construction) | Quietly left off, adding ~10% at the end |
Where the surprises actually hide
These are the line items that turn a “$300K project” into a “$380K project” — and they’re the ones most likely to be missing from a thin bid.
Utility connections (the #1 surprise)
This is the most-cited shock in Seattle ADU forums. Real homeowner numbers:
- “Typically for a legal ADU you have to pay sewer companies for the right to connect which can be anything from $10k to $40k.”— a Seattle homeowner on Reddit
- A separate meter / SPU connection starting around $15,000
- Water-meter upsizing: “The city charges over $12k to swap out to a bigger one.”— a homeowner on Reddit
Seattle also reports every ADU permit to King County for sewer treatment capacity charges— a fee a generic bid will not mention. Ask for it by name.
Soft costs (design, permits, studies)
Industry guidance puts soft costs at +15–20% above construction. One Seattle-area homeowner itemized their pre-construction spend before a single board went up:
“City Permit Fee: $5,000. Water Connection Fee: $5,000. Electrical Connection Fee: $4,000. Architect and Engineering: $15–20,000. $35,000 out the door before even starting construction.” — a homeowner on r/Tacoma (WA), 2023
That $35K is real, and it belongs in the bid — not in a surprise invoice three months in.
Geotech and ECAs
Seattle’s topography matters. Steep slopes (40%+) require geotechnical reports and can restrict your buildable area. A homeowner’s fear here is concrete: “I’ll spend $5K on plans and then find out I can’t build.”A complete bid prices the geotech up front, before you’re committed to a floor plan.
Sales tax
Washington taxes construction contracts. A bid that omits sales tax can look ~10% cheaper than one that includes it — for doing identical work. Always ask whether the total is tax-inclusive.
How to compare bids honestly
- Line them up category by category.Use the 11-row table above as your scoring sheet. A bid missing rows isn’t cheaper; it’s incomplete.
- Convert everything to all-in total cost— not $/sq ft. Per-square-foot numbers hide what’s included. For reference, current Seattle DADU build figures range from a network-rate floor around $350/sq ft to open-market quotes of $650–$950/sq ft, with $750–$800/sq ft cited as the open-market average (per Reddit, 2024–2026).
- Find the missing scope.When one bid is dramatically lower, the question isn’t “how did they do it cheaper?” It’s “what did they leave out?” Nine times out of ten the answer is utilities, geotech, contingency, or tax.
- Demand the contingency line. A bid with zero contingency is a bid that plans to bill you for every surprise.
- Get it in writing. Itemized scope, written allowances, and a change-order clause requiring your approval before extra work begins.
Our position: the bid is the product
We publish the line items because the research is unambiguous — transparent, itemized pricing is the single strongest trust signal Seattle homeowners respond to, and most builders won’t provide it. When most local competitors hide both their pricing and their scope, the honest bid is the differentiator.
Our bids contain all eleven categories, every time, with a stated contingency and tax line. You’ll know your utility-connection estimate before you sign, not after. If a number is an allowance, it’s labeled as one. That’s not a courtesy — it’s the only way you can compare us fairly to anyone else.
The checklist
Bring this to every estimate. Check a category only when it appears as a real, named number — not “TBD.”
- Design / architecture (plans, elevations, engineering)
- Boundary + topographic survey
- Geotechnical report (if slope/ECA)
- Permits + plan-review + impact/school fees
- Utility connections (sewer, water meter, electrical, SPU/SCL) — with a real number
- Sitework (excavation, grading, drainage, erosion control, demo)
- Foundation (footings, slab/crawlspace, waterproofing)
- Build (framing, roof, windows, MEP, insulation, drywall — to energy-code spec)
- Finishes with stated allowances
- Contingency (10–15%, stated)
- Washington sales tax (confirm tax-inclusive)
Any blank box is a future invoice.
Because they're not pricing the same scope. The low bid usually omits utility connections, geotech, contingency, or sales tax. Once you add those back, the spread narrows sharply. A homeowner who saw quotes from $100K to $200K+ on one garage conversion was looking at four different scopes, not four prices for one job.
