ADDITIONS & ADUS
Additions and ADUs, matched and permitted
A new bedroom, a second story, or a backyard cottage that pays rent. We match you with builders who've permitted this exact kind of project here — and help you get through the permit office without losing a season.
Additions fail before anyone swings a hammer. The plan that dies at the permit counter over a setback nobody checked. The quote that forgets to mention the sewer capacity charge. The builder who's framed a hundred garages but has never tied a detached unit into a house's utilities — and learns on your dime. And the timeline nobody warns you about: a detached backyard cottage is often a year-plus of your life once permits and utility work get real.
Ascent Prime matches you with a builder who has actually permitted and finaled additions or ADUs in this county — we ask for the permit numbers — and we stay reachable through the part that kills these projects: the paperwork. Here's how we vet builders and match you, from first form to final inspection. It's free for homeowners.
How the match works for an addition or ADU
Tell us what you're adding — a room over the garage, a second story, a detached backyard cottage, a mother-in-law suite for actual in-laws — and, just as important, the address. What's allowed changes by city and even by lot, so the address is the first thing we check. Then we match you with a builder whose permitted, finaled projects look like yours. You walk the site together, and you see a real bid before you commit to anything.
If the addition is part of a bigger rethink of the whole house, start with our whole-home renovation page; a bump-out that's really a kitchen expansion belongs on the kitchen remodeling page.
What we check on addition and ADU builders
On top of the standard checks — Washington L&I registration, bond, and insurance — addition and ADU work has its own failure points:
- Additions and ADUs they've permitted and finaled. We ask for the permit numbers, not the portfolio — a finished unit with no signed-off final inspection isn't finished.
- DADU experience: foundations, utility tie-ins, and separate meters. Detached work is a different skill set than a bump-out.
- Septic capacity questions on rural parcels. A second unit on a septic system can trigger a full upgrade, and a builder who doesn't ask about it up front will surprise you with it later.
- Schedule realism. Detached cottages regularly run a year-plus once permits and utility work are real — we're wary of anyone quoting half that.
What Washington law and local rules allow right now
This is the section that changes while you read it, so the honest version is: the rules are in flux, and we check your exact address before anyone draws plans. The big shift is Washington's HB 1337 (2023, codified as RCW 36.70A.681), which requires fully-planning cities to allow two ADUs per single-family lot in urban growth areas — no owner-occupancy requirement, units of at least 1,000 square feet allowed, and impact fees capped at half. Everett complied with Ordinance 3963-23, allowing two ADUs per dwelling. In unincorporated Snohomish County, current code — SCC 30.28.010, per PDS Assistance Bulletin #12 — allows one attached and one detached ADU, the detached up to 1,200 square feet, with a broader update working through Snohomish County PDS. Lynnwood's code still caps it at one ADU, with its own update pending.
When you're ready to file, city projects go through Everett Permit Services at 2930 Wetmore Ave; county parcels go to PDS. If the permit maze is the part that's stopped you cold, permit help is its own service here, and our guide to Snohomish County remodel permits walks through the county process in detail.
What additions and ADUs cost around here
The 2025 Cost vs Value report puts a new ADU at a national benchmark of $166,406. Seattle-area builders publishing 2025 figures quote garage conversions around $180,000 to $250,000, and detached backyard cottages at $300,000 to $450,000 and up — roughly $350 to $500 per square foot. Straight additions run lower: HomeAdvisor's 2025 national average is about $46,000, with second-story work at $100 to $300 a square foot. Treat these as orientation, not quotes — a garage conversion in Lynnwood is not the same job as a detached cottage on a septic parcel outside Lake Stevens, and the only bid that matters comes from a builder who's walked your site.
Questions about additions and ADUs
How much does it cost to build an ADU in Snohomish County?
Recent published figures put a detached backyard cottage in the Seattle area at roughly $300,000 to $450,000 and up, and garage conversions at $180,000 to $250,000. The 2025 Cost vs Value national benchmark for a new ADU is $166,406. Your lot, utilities, and finishes decide where you land; the firm number comes from the builder.
Can I build an ADU on my property?
Probably, if you're in a city — but it depends on your exact address. State law now pushes Washington cities to allow two ADUs per single-family lot; Everett allows two per dwelling, unincorporated Snohomish County allows one attached plus one detached, and Lynnwood's rules are mid-update. We check your parcel's zoning, setbacks, and utilities before you spend money on plans.
How long does it take to build an ADU?
Often a year or more, start to finish. Design and permit review alone can take several months, and detached units add utility trenching and tie-ins that stretch construction further. A builder quoting six months for a detached cottage is usually quoting the build only — not the whole road from sketches to final inspection.
Tell us what you want to build
Two minutes. Tell us what you're adding and the address — zoning is half the answer — and a real person replies within one business day. Your number never gets sold.
FREE FOR HOMEOWNERS