The short answer
In 2026, converting an existing garage into a fully permitted ADU in Washington State typically costs $60,000–$120,000 for an attached garage, or $90,000–$160,000 for a detached garage (DADU). That's roughly $150–$300 per square foot — about half the cost of building a new detached unit from scratch, because the slab, roof, and shell already exist. A basic garage finishing project without a kitchen or bathroom runs $15,000–$30,000.
Why now
The cheapest square footage you'll ever add
Washington's housing shortage pushed the legislature to act, and the 2023 ADU law (HB 1337) changed the math for homeowners. Cities planning under the Growth Management Act must now allow accessory dwelling units on most residential lots, owner-occupancy mandates have been rolled back in most jurisdictions, and ADU impact fees are capped well below what a primary residence pays.
The practical result: the cheapest square footage you can add is the footage you already own. A two-car garage is 400–550 sq ft of foundation, roof, and walls that's already built and already tied to your utilities. Converting it into a legal studio or one-bedroom costs a fraction of new construction — and in the Puget Sound rental market, a permitted ADU typically rents for $1,300–$1,900 per month.
See our Tacoma garage & ADU service
2026 pricing
Cost by project type
Basic finishing
$15k–$30k
2–3 weeks
Insulation, drywall, and flooring — a comfortable finished room, no kitchen or bathroom.
Attached → full ADU
$60k–$120k
8–14 weeks
Kitchenette, bathroom, and separate entrance — a legal, rentable dwelling unit.
Detached → DADU
$90k–$160k
10–16 weeks
A stand-alone unit with its own utility connections and site work.
Construction timelines exclude design and permit review (typically 4–10 additional weeks by jurisdiction).
Where the money goes
Line-item breakdown
A typical attached-garage ADU conversion in Western Washington. Bar length shows each line's share of a mid-range budget — the wet areas dominate, which is exactly where finish quality pays you back.
The biggest quality-and-value lever in that list is the wet areas. A properly waterproofed tile installation in the shower and durable tile flooring in the kitchen zone are what make an ADU feel like a real home at appraisal — and keep a rental low-maintenance for the next decade.
Inside the build
What your budget actually buys
Cabinets, counters, and appliances scaled to a compact footprint.
A waterproofed tile shower — the single biggest value lever in the unit.
Clean transitions are what separate "converted garage" from "nicest unit on the block."
The variables
What drives the price up or down
Electrical panel capacity. Many 1970s–1990s homes run 100–125A service. Adding a kitchen and heat often needs a panel upgrade or dedicated subpanel — budget $3k–$8k if yours is maxed.
Distance to plumbing. If the garage sits far from your main drain — or the lot is on septic — trenching and connections can add $5k–$15k. Detached garages feel this most.
Slab & ceiling condition. Habitable rooms need code-compliant ceiling heights; a cracked or sloped slab needs leveling before finished flooring goes down.
Wet zones on one wall. Stacking the bathroom and kitchenette against the house-side wall shortens every pipe run and can save five figures on a detached unit.
Attached over detached. An attached garage shares heat, walls, and utilities with your home. Given the choice, the attached conversion nearly always pencils better.
State-capped impact fees. Under Washington's ADU reforms, accessory-unit impact fees are capped at a fraction of a primary residence's — verify the current schedule before budgeting old numbers.
Paperwork
Permits & timeline in Pierce and King County
A garage conversion is not a cosmetic remodel in the eyes of your building department. Turning unconditioned garage space into habitable area triggers requirements for insulation and energy code, egress windows, minimum ceiling height, ventilation, smoke and CO detection, and inspected electrical and plumbing work. That permit trail is what makes the unit legal to rent and countable at appraisal.
In unincorporated Pierce County — including Lake Tapps, where we're headquartered — permits run through Pierce County Planning & Public Works. Tacoma, Auburn, Bonney Lake, and King County cities each have their own review queues. Realistic 2026 review times run 4–10 weeks by jurisdiction and drawing completeness.
As a licensed general contractor (WA #604-916-590), we run the whole path — zoning check, drawings, submission, inspections, and final sign-off — so the timeline risk sits with us, not you.
The return
What a garage ADU earns back
Two numbers matter: rent and resale. In 2026, permitted studio and one-bedroom ADUs in Pierce County typically rent for $1,300–$1,900 per month; closer to Seattle and Bellevue, $1,800–$2,500 is common. Against a $75,000–$100,000 conversion, that's a gross payback of roughly 4–7 years — before counting added property value.
On resale, appraisers increasingly credit permitted ADUs as income-producing square footage, and a well-finished unit typically adds $40,000–$80,000 in appraised value depending on market and finish. The keyword is permitted — an unpermitted conversion can subtract value and stall a sale.
Multigenerational living is the return that doesn't show up on a spreadsheet: a parent aging in place, a college kid staying close, a home office that isn't the kitchen table. The same unit serves all three over its life.
Play it smart
Five ways to keep your conversion on budget
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1
Verify zoning before design. A one-hour feasibility check against your parcel beats redrawing plans after a rejection.
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2
Fix scope before demolition. Mid-project changes are the #1 budget killer — lock the kitchenette layout and tile selections up front.
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3
Put money in the envelope and wet areas. Insulation, windows, waterproofing, and tile are the layers you can't cheaply redo. Paint and fixtures you can upgrade any year.
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4
Use one design-build contractor. Separate designers, plumbers, and GCs mean three schedules and three markups. One accountable team compresses both.
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5
Match the exterior to your home. Infilling the garage door with siding that matches the main house is what keeps the conversion from looking like one — and protects resale value.
Good to know
Frequently asked questions
Is converting a garage to an ADU cheaper than building a new one?+
Yes, usually by a wide margin. A conversion reuses the existing slab, roof, and shell, saving $30,000–$60,000 versus a ground-up detached ADU. Most attached conversions land between $60,000 and $120,000, while new-construction DADUs often start around $150,000.
How much do ADU permits cost in Washington?+
Plan on $4,000–$12,000 all-in for drawings, applications, and plan review, depending on jurisdiction and complexity. Washington's 2023 ADU law (HB 1337) also capped ADU impact fees at a fraction of a primary residence's, lowering soft costs in many cities.
How long does a garage-to-ADU conversion take?+
Expect 4–10 weeks for design and permitting, then 8–14 weeks of construction. A realistic start-to-finish timeline in the Puget Sound area is 4–6 months, driven mostly by permit queues and material lead times.
Can I rent out my garage ADU in Washington?+
Yes. Once permitted and passed final inspection, it can be rented long-term in virtually every Washington jurisdiction, and owner-occupancy requirements have been rolled back in most cities. Short-term rental rules vary by city, so verify locally before listing on Airbnb-style platforms.
Does a garage ADU increase property taxes?+
Usually yes — permitted living space raises your home's assessed square footage, and the county assessor reflects that in a higher valuation. For most owners, the rental income ($1,300–$1,900/month for a typical Pierce County unit) far outweighs the tax increase.
Do I need an architect to convert my garage into an ADU?+
Not always. Simple attached-garage conversions can usually be permitted with drafted plans rather than architect-stamped drawings. Structural changes, additions, or detached units may require an engineer's stamp. A design-build contractor like ViOrigin prepares and submits the drawings as part of the project.
Get an exact number for your garage
Ranges are for articles — your parcel deserves a real quote. We'll check your zoning, walk the space, and give you a written estimate. Free, and usually within days: we're based in Lake Tapps and serve all of Pierce and King County.
Or call (253) 339-3784