Garage Conversion

Garage Conversions in Bellevue, Seattle and the Eastside: What to Expect

A garage is the cheapest square footage you already own. The slab, walls and roof are built, which is why converting one is usually the fastest and least expensive way to add a family room, home office, gym, guest suite or a fully self-contained ADU in Seattle, Bellevue, Kirkland, Redmond, Bothell, Renton and across King County. Blue Lake Construction handles the design, permits and construction of garage conversions under one fixed-price contract, as a licensed Washington general contractor (#BLUELLC760C3).

How much does a garage conversion cost in the Seattle area?

For a standard two-car garage of about 400–480 sq ft, converting it to insulated, heated living space with drywall, flooring and egress windows typically runs $60,000–$120,000 in 2026. Converting it to a complete ADU with a kitchen, bathroom, laundry and separate entrance typically runs $120,000–$250,000. The biggest cost drivers are leveling the sloped slab, new plumbing runs, an electrical panel upgrade or subpanel, and bringing insulation and heating up to Washington's energy code. Every project gets a fixed, itemized price before work begins.

Do I need a permit to convert a garage in Washington?

Yes, everywhere in King County. A conversion changes the use of the space from parking to habitable, so a building permit is required, plus electrical, plumbing and mechanical permits for the systems you add. Add a kitchen and the space becomes an accessory dwelling unit, which brings zoning review; under Washington's HB 1337, Seattle, Bellevue, Kirkland, Redmond and other cities must now allow ADUs on most residential lots, and parking rules have been relaxed. We confirm the rules for your specific lot, prepare the drawings and pull every permit for you.

Garage conversion or a new DADU: which is the better choice?

A conversion wins on price and speed: reusing the shell typically saves $100,000 or more compared with ground-up construction, and construction takes about 2–4 months instead of 4–8. A new detached ADU wins on layout and value, with full-height ceilings, better siting and a purpose-designed floor plan that usually rents and appraises higher. If your garage is structurally sound, well located and you can live without the covered parking, a conversion is usually the smart first step; we price both options as fixed bids so you can compare.

What does it take to make a converted garage comfortable year-round?

Four things: a level, insulated floor over the old slab; insulated walls and ceiling that meet the Washington State Energy Code; a dedicated heat source, usually a ductless mini-split heat pump that also cools in summer; and real windows plus a code-compliant egress opening where the garage door used to be. Sound insulation and a properly flashed infill wall keep the space quiet and dry through nine months of Puget Sound rain.