Straight
answers.
45 deeply researched questions on building an ADU in the Puget Sound — every number is current, every code citation is real, every link goes to the workings.
Timeline
TimelineHow long does a detached ADU take from kickoff to keys?
How long does a detached ADU take from kickoff to keys?
Plan on 8–12 months end-to-end: 6–10 weeks for design and engineering, 12–20 weeks in permit review, and 16–24 weeks of active construction. Schedules tighten when the lot is flat, the design uses a pre-approved plan, and utility upgrades are minimal.
See full timelineTimelineHow fast can a garage conversion (AADU) finish?
How fast can a garage conversion (AADU) finish?
Garage conversions and attached ADUs typically deliver in 3–5 months: 4–6 weeks of design, 8–12 weeks of permitting, and 8–14 weeks of construction. The existing slab and walls usually shave 30–40% off both the schedule and the budget compared to a new DADU.
Garage conversion serviceTimelineHow long is permit review in Seattle, Bellevue, Kirkland, and Tacoma?
How long is permit review in Seattle, Bellevue, Kirkland, and Tacoma?
As of this quarter: Seattle SDCI averages 12–16 weeks, Bellevue 8–12 weeks, Kirkland 6–10 weeks, and Tacoma 8–14 weeks. Pre-approved DADU plans cut Seattle review to 4–6 weeks. We track jurisdiction velocity weekly and quote permit windows from current data, not last year's averages.
Seattle permitsTimelineWhat can delay an ADU project, and how do you defend against it?
What can delay an ADU project, and how do you defend against it?
The three usual culprits are city correction cycles, side-sewer capacity surprises, and long-lead specialty items (windows, panels, custom millwork). We mitigate by pre-checking sewer capacity at design, ordering long-lead items at permit submittal, and assigning a permit expediter to every project.
TimelineDo you build through Pacific Northwest winters?
Do you build through Pacific Northwest winters?
Yes. Foundations are sequenced for the drier shoulder seasons when possible, but framing and finish work continue year-round under temporary weather protection. Our schedules include a documented weather contingency (typically 10–15 working days) so winter rain doesn't push your handover.
Cost
CostWhat does a detached ADU actually cost in 2026?
What does a detached ADU actually cost in 2026?
Most of our turn-key DADUs land between $325,000 and $525,000, or roughly $400–$525 per square foot all-in (design, permits, site work, build, and warranty). The spread is driven by size, finish tier, and how much the lot fights you — slope, trees, and utility distance are the big movers.
Seattle cost breakdownCostWhat does an attached ADU (AADU) or basement conversion cost?
What does an attached ADU (AADU) or basement conversion cost?
AADUs and basement conversions typically run $185,000–$310,000. They benefit from shared walls, existing utilities, and a smaller permit scope, but ceiling height, egress windows, and separate-entry framing can quietly add $20K–$40K if the existing house wasn't designed for it.
CostWhat does a garage conversion cost?
What does a garage conversion cost?
Garage conversions usually fall between $145,000 and $235,000 depending on whether the slab needs to come up, the roof needs structural reinforcement, and how far the kitchen/bath plumbing runs to the existing main line. The single biggest variable is insulation upgrades — most older garages need full envelope work to meet code.
CostWhat's the price per square foot — and why is that number misleading?
What's the price per square foot — and why is that number misleading?
Our DADUs pencil to roughly $400–$525/sqft, AADUs $325–$425/sqft, and garage conversions $300–$425/sqft. The number is useful for sanity checks, but smaller ADUs always cost more per sqft because kitchens, baths, and utility hookups don't scale down. Compare total project cost against scope, not /sqft against /sqft.
CostDo you bid fixed-price or time-and-materials?
Do you bid fixed-price or time-and-materials?
Every contract is a fixed-price agreement signed after design and engineering are complete. We don't bid T&M for ADUs because the scope is knowable — anyone who insists on T&M is asking you to absorb their risk. The only variable line items are owner-selected allowances (appliances, plumbing fixtures, flooring) that you control.
CostHow accurate is your free consultation budget range?
How accurate is your free consultation budget range?
Our consult-stage range is typically ±15% of the eventual fixed-price contract. We tighten that to ±3% during schematic design after the survey and geotech are in. If a competitor is offering ±0% before you've paid for engineering, they're either padding the number or about to write change orders.
Financing
FinancingHow do most clients pay for an ADU?
How do most clients pay for an ADU?
Roughly 55% use a HELOC or cash-out refi against existing home equity, 30% use a renovation construction loan (Fannie HomeStyle, FHA 203k, or a local credit union ADU product), and 15% pay cash. We don't lend, but we make warm intros to four Puget Sound lenders who actually understand ADU draws.
Financing optionsFinancingWhat's an ADU construction loan and when does it make sense?
What's an ADU construction loan and when does it make sense?
It's a single-close loan that funds construction in draws and converts to a permanent mortgage at handover, underwritten on the post-construction appraised value of your property (house + ADU). It makes sense when you don't have enough existing equity to cover the build but the finished-value math pencils — common for newer purchases.
FinancingWill an ADU appraise for what it costs to build?
Will an ADU appraise for what it costs to build?
In most King and Pierce County neighborhoods, a well-built DADU appraises for 80–110% of build cost — better when there are recent comparable ADU sales nearby. The 'appraisal gap' is real but shrinking fast as ADU comps accumulate; we share recent appraisal data for your zip during the consult.
FinancingAre there grants, rebates, or tax incentives for building an ADU?
Are there grants, rebates, or tax incentives for building an ADU?
Seattle's pre-approved DADU program waives ~$3K in plan-review fees. Puget Sound Energy and Seattle City Light offer heat-pump and induction rebates ($500–$2,500). Washington has no state income tax, but ADU rental income is federal-taxable; bonus depreciation on the structure can shelter much of it — talk to a CPA.
Design
DesignDo you have in-house architects or use outside firms?
Do you have in-house architects or use outside firms?
Architecture, interior design, and structural engineering are in-house. MEP (mechanical, electrical, plumbing) and civil are long-term partners we've worked with for 8+ years. One contract, one accountable schedule, no finger-pointing when something needs to change.
Our processDesignHow many design revisions are included?
How many design revisions are included?
Three rounds of schematic revisions are baked into the design fee, which is enough for 95% of projects. We deliberately front-load the first round with three distinct floor-plan options so you're choosing between real alternatives, not nudging a single plan around.
DesignCan you match the architecture of my existing house?
Can you match the architecture of my existing house?
Yes — we routinely match Craftsman, mid-century, Tudor, and contemporary primary homes. Roof pitch, eave depth, window proportions, siding rhythm, and trim profiles are documented from your house at the site visit and carried into the ADU drawing set so the result reads as one property, not two.
DesignCan the ADU be designed for aging-in-place or accessibility?
Can the ADU be designed for aging-in-place or accessibility?
Yes, and we recommend it for primary-home owners over 55. Standard accessible upgrades — 36" doors, zero-step entry, blocking for future grab bars, roll-in shower, accessible kitchen heights — add $8K–$18K to a DADU and keep the unit useful for the next 40 years.
DesignShould I use a pre-approved plan or design from scratch?
Should I use a pre-approved plan or design from scratch?
Seattle's pre-approved DADU plans save 4–8 weeks of permitting and ~$15K–$25K in design fees, but they're sized and styled for typical lots. Custom design wins when the lot is unusual (sloped, narrow, view-driven) or when you want the ADU to match a specific architectural language. We build both.
Permitting
PermittingWho pulls the permits — me or you?
Who pulls the permits — me or you?
We do, every time. Golden acts as the permit applicant, manages all city corrections, schedules inspections, and closes the permit at final. You'll see every submission and correction in your project portal, but you never wait in line at SDCI.
PermittingHow does Seattle's SDCI ADU permit process actually work?
How does Seattle's SDCI ADU permit process actually work?
Two parallel tracks: a building permit (structural, envelope, energy) and a side-sewer/water permit. SDCI typically issues a first correction round at week 6–8, a second at week 11–13, and approval at week 14–16. Pre-approved plans skip the first review entirely.
Seattle permits guidePermittingHow is Bellevue different from Seattle for ADU permits?
How is Bellevue different from Seattle for ADU permits?
Bellevue review is faster (8–12 weeks) but stricter on tree retention, impervious-surface limits, and design review for ADUs over 800 sqft. Setback rules are also more conservative on R-1 lots. We pre-flight every Bellevue submittal against the current bulletin set.
Bellevue permits guidePermittingWhat about Kirkland, Redmond, and Tacoma?
What about Kirkland, Redmond, and Tacoma?
Kirkland (6–10 weeks) and Redmond (8–12 weeks) both allow DADUs by right in most residential zones with relatively predictable review. Tacoma (8–14 weeks) is the friendliest for AADUs and basement conversions thanks to recent zoning reform. Each city has its own quirks — we maintain an internal cheat-sheet per jurisdiction.
PermittingDo I need a land-use or design review before the building permit?
Do I need a land-use or design review before the building permit?
For most single-family ADUs in Seattle, Bellevue, and Kirkland: no. Design review kicks in for ADUs in landmark districts, environmentally critical areas (steep slope, wetland, liquefaction), or shoreline jurisdiction. We screen for all three on day one of the consult.
Zoning & Lot
Zoning & LotWhat's the minimum lot size for a DADU?
What's the minimum lot size for a DADU?
Seattle removed minimum lot-size requirements for DADUs in 2019 — if you have a single-family lot, you almost certainly qualify. Bellevue requires 5,000 sqft, Kirkland 7,200 sqft (with exceptions), and Tacoma 5,000 sqft. We confirm your lot's eligibility for free during the consult.
Zoning lookupZoning & LotWhat are the setback and height rules?
What are the setback and height rules?
Seattle: 5 ft side/rear setbacks, 18 ft height (23 ft with pitched roof). Bellevue: 5 ft sides, 10 ft rear, 24 ft height. Kirkland: 5/10/25. These shrink your buildable footprint more than people expect — we plot the buildable envelope on day one before drawing anything.
Zoning & LotHow much square footage am I allowed to build?
How much square footage am I allowed to build?
Seattle allows DADUs up to 1,000 sqft (1,200 sqft with a green-building bonus). Bellevue caps at 1,000 sqft. Kirkland at 800–1,200 sqft depending on lot size. The cap and the lot's FAR (floor-area ratio) interact — large existing houses on small lots sometimes hit FAR before they hit the ADU cap.
Zoning & LotDoes Seattle's tree code affect where I can build?
Does Seattle's tree code affect where I can build?
Yes, and it's the single most common surprise. Trees ≥6" diameter in single-family zones are protected; building within their critical root zone requires an arborist report and may require relocation of the ADU. We run a tree-survey overlay before schematic design so you never invest in a plan the trees won't allow.
Zoning & LotWhat if my side sewer or electrical service isn't big enough?
What if my side sewer or electrical service isn't big enough?
Side-sewer capacity is checked against existing fixture count plus ADU fixture count; if you're over, a sewer-cap calc or full sewer replacement is required ($8K–$25K). Electrical: most ADUs need a 100A or 200A subpanel; if the main service is 100A you'll likely upsize ($4K–$12K). We diagnose both at the site visit.
Rentals & Income
Rentals & IncomeCan I rent out the ADU long-term?
Can I rent out the ADU long-term?
Yes — long-term rentals (30+ day leases) are allowed in every city we build in. Seattle, Bellevue, Kirkland, and Tacoma all require a basic rental registration ($55–$175/year) and a periodic inspection (every 5–10 years depending on city).
Rentals & IncomeCan I run it as a short-term rental (Airbnb)?
Can I run it as a short-term rental (Airbnb)?
Rules vary sharply by city. Seattle: yes, with a short-term rental license and operator's license — owner doesn't need to live on site, but the unit must be one of only two STR licenses per operator. Bellevue and Kirkland: only with owner-occupancy of either the primary house or the ADU. Tacoma is the most permissive. Always verify current code before counting on STR income.
Rentals & IncomeShould the ADU have separate utility meters?
Should the ADU have separate utility meters?
For long-term rentals: usually yes for electric ($3K–$5K), optional for water and gas. For STR or family use: a single meter with sub-billing software ($400–$800) is usually cheaper. Separate meters increase appraised value modestly and simplify future sale or condo-conversion.
Rentals & IncomeDo I have to live on the property to build an ADU?
Do I have to live on the property to build an ADU?
No. Seattle removed owner-occupancy requirements in 2019. Bellevue, Kirkland, and Tacoma also allow non-owner-occupied ADUs, though some cities require it if you want a short-term rental permit (see above). This means ADUs are a legitimate investment-property play, not just a backyard cottage for relatives.
Construction
ConstructionHow disruptive is construction to my daily life?
How disruptive is construction to my daily life?
Plan on 16–24 weeks of weekday site activity (7am–5pm), peak noise during demo, foundation, and framing (~4 weeks total). We provide a job-site contact, weekly written progress reports, and a single point of escalation. Driveway access is preserved except for 1–2 short closures we schedule with you in advance.
ConstructionWill my utilities (water, power, internet) be interrupted?
Will my utilities (water, power, internet) be interrupted?
Brief planned shutoffs only: typically one 4–6 hour water shutoff for the side-sewer tie-in, and one 2–4 hour power interruption when the meter is upgraded or the subpanel is energized. Internet is never affected. All shutoffs are scheduled with you at least 5 business days ahead.
ConstructionWhat happens to parking and street access during the build?
What happens to parking and street access during the build?
We secure a city right-of-way permit when a dumpster, port-a-john, or storage container needs the curb. Crew vehicles park off-site when possible. On tight urban lots we coordinate with neighbors before mobilization and provide a written disruption schedule — most complaints come from surprises, not the work itself.
ConstructionDo you notify the neighbors?
Do you notify the neighbors?
Yes. We hand-deliver a project intro letter to immediate neighbors before mobilization with the schedule, our site supervisor's direct line, and the city permit number. Cities like Seattle also post a public notice of construction — we handle that filing as part of the permit package.
Warranty & Trust
Warranty & TrustWhat warranty do I get on the finished ADU?
What warranty do I get on the finished ADU?
1-year comprehensive workmanship warranty on everything we built and installed, 2 years on mechanical/electrical/plumbing systems, and 10 years on the structural envelope (foundation, framing, roof). Manufacturer warranties on appliances, windows, and roofing pass through to you directly.
Warranty termsWarranty & TrustAre you licensed, bonded, and insured?
Are you licensed, bonded, and insured?
Yes — active Washington general contractor license GOLDNAB882L2 (verifiable at lni.wa.gov), $25,000 contractor bond, $2M general liability, and full workers' comp coverage on every employee and subcontractor. Certificates of insurance are sent to you and your lender before mobilization.
Warranty & TrustHow do change orders work?
How do change orders work?
Any scope change goes through a written change order with a fixed price and schedule impact before any work happens — no exceptions. About 70% of our projects close with zero owner-initiated change orders. The remaining 30% usually add owner upgrades (better appliances, an extra skylight) rather than fix surprises.
Process
ProcessWhat happens during the free consultation?
What happens during the free consultation?
A 45-minute on-site or video walkthrough. We review your zoning, plot a buildable envelope, identify any tree/sewer/setback constraints, and give you a written budget range and timeline within 48 hours. No deposit, no obligation, no upselling.
Book a consultationProcessWhat's the payment schedule once we sign?
What's the payment schedule once we sign?
Standard schedule: 10% at design kickoff, 15% at permit submittal, 20% at foundation, 20% at framing dry-in, 20% at drywall, 10% at substantial completion, 5% at final/punch-list closeout. Construction-loan draws are billed on the same milestones.
ProcessHow do I know my project is on schedule and on budget?
How do I know my project is on schedule and on budget?
Every client gets access to a project portal with the live schedule, weekly photo logs, every permit submission and correction, every signed change order, and a real-time budget tracker. The same data is summarized in a Monday morning email so you don't have to log in to know where things stand.
Didn't find your answer?
Talk to a senior builder, not a sales rep. 45-minute consult, written budget within 48 hours, no obligation.