What a garage conversion costs in Seattle in 2026 — by scope. In Kolmo's calculators a 1- or 2-car garage runs from about $10,800 for a kept-door bonus room to about $98,500 for a full ADU-style suite, a legal unit priced by our ADU calculator. Figures include permits and the base contingency. For the room conversions, garage-door infill, cladding match and new windows are quoted after a site visit; the suite's price includes the door infill. Pre-1978 homes add 8–10%.
This page is a cost guide, not a calculator of its own. For an instant number on a full legal-unit conversion, use the ADU calculator and choose its Garage-conversion ADU type. For a room-only conversion, use the basement calculator (closest scope). For other project types, see the full calculator hub.
Tell us the garage footprint and target scope (bonus room, guest suite, or ADU) and we'll come back with a detailed line-item estimate within 48 hours. No obligation, no sales pressure.
Ranges run from a typical 1-car (~250 sq ft) to a 2-car (~450 sq ft) garage, permits and base contingency included. The three room conversions come from our basement calculator; the ADU-style suite comes from our ADU calculator's garage-conversion type. For the room conversions, garage-door infill, cladding match and new windows are quoted on site; the suite's price includes the door infill. Homes built before 1978 add 8–10% contingency for asbestos, lead, and knob-and-tube risk.
$10,800-$12,800
Garage door stays in place (with upgraded insulated panels). The space is conditioned and finished but isn't habitable living space by code — great for a gym, workshop, or playroom.
$14,200-$21,300
Garage-door-to-wall infill creates a permanent room. No bath, no kitchen — just a clean conditioned bonus space. Seattle's most common garage conversion.
$29,900-$37,000
Adds a full bath with rough plumbing and a sub-panel if needed. Often used as a guest suite or in-law setup. Triggers SDCI permit and inspection.
$76,500-$98,500
A legal ADU inside the existing garage shell, priced by our ADU calculator's garage-conversion type: one rate per sq ft set by the finish tier, plus permit, design and contingency. Requires SDCI ADU permit.
Line items a garage conversion has that a basement or bathroom remodel doesn't.
In Kolmo's calculators a 1- or 2-car Seattle garage conversion runs about $14,200-$21,300 for a conditioned bonus room (no bath), $29,900-$37,000 with a full bath, and $76,500-$98,500 for a full ADU-style suite, a legal unit priced by the ADU calculator. For the room conversions, garage-door infill, cladding match and new windows are quoted after a site visit; the suite's price includes the door infill. Pre-1978 homes add 8-10% contingency.
Remove door + tracks, frame a stud wall matching exterior, install window or patio door, match exterior cladding, patch drywall. For a room conversion we quote it after a site visit because the cladding match drives the cost; the ADU-style suite's price includes it. Most Seattle conversions add a 4-ft window so the room doesn't feel cave-like. A dedicated entry door is quoted separately.
Almost always yes. Converting garage to habitable space triggers SDCI review — you're adding assessed sq ft. Legal bedroom needs egress window (IRC R310). A full ADU permit is larger: energy-code envelope compliance, soundproofing to main home, potentially separate address. Check /permits for your specific project.
Yes. A kept-door bonus room with wall and ceiling insulation, drywall, and an LVP floor runs about $10,800-$12,800; the insulated garage door, electrical and heat are quoted separately. Seattle doesn't treat this as habitable living space (can't be a bedroom, doesn't count toward home sq ft), but it's legal and useful for a gym, workshop, or playroom.
Two paths. Extend main-home ductwork (about $2,520) if existing HVAC has 500-800 sq ft of spare capacity. Or a ductless mini-split (about $4,520 installed) — dedicated zone, independent temperature control, HOMES-rebate eligible when paired with envelope upgrades. Mini-splits are the default for full ADU conversions.
Yes, for a full legal unit: the ADU calculator at /calculator/adu has a Garage-conversion ADU type that prices the conversion per sq ft, door infill included, plus permit, design and contingency. For a room-only conversion, the basement calculator at /calculator/basement prices the conditioned finish (~80% scope overlap); garage-door infill and other garage-specific items are quoted after a site visit. Best path for a firm number: request a quote via the button above — 48-hour response.
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Seattle garage conversion costs in 2026: $10.8K for a bonus room to $129K+ for a full ADU. Real $ by scope, SDCI permit rules, egress, and a line-item breakdown.
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Permit fees, utility separation, soundproofing, attached-vs-detached tradeoffs.
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