Can my detached garage be legally converted to a rental in Seattle?

Most can. SDCI treats a detached garage conversion as a DADU when it adds a kitchen and bath. The slab must meet frost-depth and moisture-barrier requirements (often retrofitted), and the structure typically needs new shear walls, a foundation upgrade, and full insulation per WSEC 2021.

Do I have to keep a parking space if I convert my garage?

No. Seattle removed off-street parking minimums for ADUs in 2019, and HB 1337 prevents cities from requiring replacement parking for an ADU within a half-mile of major transit. Bellevue, Kirkland and Redmond follow the same rule.

How do I deal with the uninsulated concrete slab during a garage conversion?

We saw-cut for plumbing, install a 10-mil vapor barrier and 2 in. of XPS rigid insulation, then pour a new wear slab or float a self-leveling underlayment. That meets WSEC 2021 R-10 under-slab requirement and stops the cold-floor and condensation issues garages are notorious for.

Will a garage conversion need a new electrical service?

Usually a dedicated 100A or 125A sub-panel from the main is enough. Seattle City Light only requires a service upgrade when total demand exceeds existing capacity (often 200A). We do a load calc as part of feasibility so the number is firm before permit.

How long does a garage conversion take in the Seattle area?

3–4 months on site once SDCI issues the permit. Permit review for a garage-to-DADU conversion is typically 2–4 months at SDCI, faster in Bellevue and Kirkland. Total contract-to-keys is usually 5–8 months.

Can I convert an attached garage instead of a detached one?

Yes — that's classified as an AADU (attached) rather than a DADU. The fire-rated wall between the new unit and the rest of the house must be upgraded to 1-hour rated assembly, and a separate entry is required. Cost is usually 10–15% lower than a comparable detached conversion.

What is included in GARAGE CONV.?

Our GARAGE CONV. scope includes design through completion: feasibility, schematic design, construction documents, permit submittal and review management, construction with one self-performed framing crew plus L&I-licensed MEP subcontractors, all required WA inspections, certificate of occupancy, and warranty. One contract, one license number, one warranty — not a coordination headache across five vendors. Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide (/guides/garage-conversion-timeline).

How is GARAGE CONV. different from a generic remodel?

GARAGE CONV. carries code, permit, and construction details that a one-off remodeler hasn't repeated enough times to optimize. Examples: IECC R406 envelope path selection, fire separation when units are within 5 ft, side-sewer slope requirements, IRC Appendix AQ when permitted as a tiny house, separate utility metering rules. We do this scope every month — repetition is what makes our first-cycle approval rate and our schedule reliability stand out.

What is the typical price range for GARAGE CONV.?

GARAGE CONV. pricing in 2026 lands $330–$380/sqft all-in depending on size, lot conditions, finish tier, and AHJ. The wide range is real — small lots with difficult access, soils requiring pier-and-beam, or service upgrades push the upper end; flat lots with good access and a catalog plan land at the lower end. Our feasibility report gives you a ±15% number tailored to your specific lot in two weeks. Go deeper: Seattle ADU cost breakdown (/cost/seattle).

What permits does GARAGE CONV. require?

Standard GARAGE CONV. permit stack: building permit (covers structural, mechanical, plumbing under combined review), side-sewer permit, water meter capacity check, electrical permit, drainage review where applicable, addressing application. Critical-areas review triggers on lots mapped for steep slope, wetland, riparian, or landslide hazard. We pull all permits as a pass-through line in our contract — not marked up. Go deeper: Read the King County side sewer permits for ADUs: cost & timeline (2026) guide (/guides/king-county-side-sewer-permits).

How long does GARAGE CONV. take from contract to completion?

9–14 months end-to-end is typical for GARAGE CONV.: 6–8 weeks design, 8–16 weeks permit, 18–26 weeks construction. Faster on catalog plans with pre-app meetings. Schedule variance is driven by AHJ workload, owner selection pace, and any field-discovered conditions. We publish a Gantt at contract and update it weekly. Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide (/guides/garage-conversion-timeline).

What's the warranty on GARAGE CONV.?

One year workmanship, two years mechanical (HVAC, plumbing rough, electrical rough), 10 years structural per RCW 4.16.310. Manufacturer warranties pass through directly: LP SmartSide siding 50-year, GAF Timberline HDZ shingles, Marvin window 20-year, Bosch/GE appliances 1-year. Documented in a written warranty packet at closeout. Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide (/guides/garage-conversion-timeline).

Do you self-perform GARAGE CONV. work or subcontract everything?

We self-perform framing, exterior weather barrier, interior trim, and project supervision with W-2 carpenters. MEP trades (plumbing, electrical, HVAC) are subcontracted to L&I-licensed specialty contractors we've worked with 5+ years — WA requires separate PL, EL, HVAC/R licenses that a GC cannot legally self-perform without them. Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide (/guides/garage-conversion-timeline).

What's the change-order policy on GARAGE CONV.?

Every change order is written, priced, and signed before work proceeds. We never charge T&M without a not-to-exceed. Owner-initiated changes carry 15% OH&P; field-discovered conditions (rotted sheathing, undocumented buried oil tank, unmapped sewer) are priced at cost +10% with photo documentation. Average GARAGE CONV. project sees 4–7 change orders totaling 3–6% of contract value. Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide (/guides/garage-conversion-timeline).

What financing works for GARAGE CONV.?

HELOC (fastest, 8.0–9.5% APR), renovation loan (Fannie HomeStyle / Freddie CHOICERenovation, 7.1–7.9%), construction-to-perm (best for ground-up), or cash-out refi (only if existing rate above market). WSHFC's ADU pilot at ~3.5–4.25% applies to ADU-scoped GARAGE CONV. projects for income-qualified owners. Go deeper: Seattle ADU financing options (/financing/seattle).

Do you provide references for GARAGE CONV. work?

Yes — we provide 5+ GARAGE CONV. references on request: past clients in your target city, your target neighborhood when possible, and at your target scope. References include name, phone, project address, and a one-paragraph project summary. We refresh the reference list quarterly so the contacts are recent and reachable. Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide (/guides/garage-conversion-timeline).

SPEC_03 / Garage

GARAGE CONV.

Garage conversions are the fastest path to an income-producing or family-flex space on a small lot. We address the issues every garage has — uninsulated slab, no vapor barrier, undersized electrical, single-pane glass — and deliver a quiet, dry, code-legal living space.

START THIS PROJECT COST GUIDE

Deliverables

SPEC_03.A

01Slab inspection + moisture mitigation
02Wall & ceiling insulation upgrades
03Window/door re-framing
04Sub-panel + dedicated circuits
05Mini-split HVAC system
06Finish carpentry + paint

Spec sheet

SPEC_03.B

+Closed-cell spray foam (R-21 walls)
+Self-leveling moisture-barrier underlayment
+Mitsubishi Hyper-Heat mini-split
+Marvin Essential black-clad windows
+Engineered LVT or polished concrete

ADJACENT_SPECS

01 //

DETACHED ADU

Stand-alone backyard cottages built from the ground up — engineered for rental income, multi-generational living, or your home office.

02 //

ATTACHED ADU

Seamlessly integrated additions — basement, ground-floor, or wing conversions that maintain the architectural integrity of your existing home.

04 //

MODERN ADDITIONS

Structural expansions for growing families — second stories, primary suites, kitchen extensions. Steel, glass, and Pacific Northwest materials.

ARCHIVE_02 / Field Reports

Recent Garage projects

Full archive →

REF_4218 · Mar 2024
Kirkland Garage Studio
Kirkland, WA · 480 sqft
Two-car garage transformed into a high-end work-from-home studio with skylight.

Full archive →

Garage questions

SPEC_03.FAQ

Real questions from Seattle, Bellevue, Kirkland and Eastside owners evaluating a garage conv. project. Code references are current as of 2025 — confirm with us during feasibility.

Q.01
Can my detached garage be legally converted to a rental in Seattle?
Most can. SDCI treats a detached garage conversion as a DADU when it adds a kitchen and bath. The slab must meet frost-depth and moisture-barrier requirements (often retrofitted), and the structure typically needs new shear walls, a foundation upgrade, and full insulation per WSEC 2021.
Q.02
Do I have to keep a parking space if I convert my garage?
No. Seattle removed off-street parking minimums for ADUs in 2019, and HB 1337 prevents cities from requiring replacement parking for an ADU within a half-mile of major transit. Bellevue, Kirkland and Redmond follow the same rule.
Q.03
How do I deal with the uninsulated concrete slab during a garage conversion?
We saw-cut for plumbing, install a 10-mil vapor barrier and 2 in. of XPS rigid insulation, then pour a new wear slab or float a self-leveling underlayment. That meets WSEC 2021 R-10 under-slab requirement and stops the cold-floor and condensation issues garages are notorious for.
Q.04
Will a garage conversion need a new electrical service?
Usually a dedicated 100A or 125A sub-panel from the main is enough. Seattle City Light only requires a service upgrade when total demand exceeds existing capacity (often 200A). We do a load calc as part of feasibility so the number is firm before permit.
Q.05
How long does a garage conversion take in the Seattle area?
3–4 months on site once SDCI issues the permit. Permit review for a garage-to-DADU conversion is typically 2–4 months at SDCI, faster in Bellevue and Kirkland. Total contract-to-keys is usually 5–8 months.
Q.06
Can I convert an attached garage instead of a detached one?
Yes — that's classified as an AADU (attached) rather than a DADU. The fire-rated wall between the new unit and the rest of the house must be upgraded to 1-hour rated assembly, and a separate entry is required. Cost is usually 10–15% lower than a comparable detached conversion.

AUTHORITY / Verify the spec

Official resources & sources

PLAYBOOK / GARAGE_CONVERSION

What a code-legal garage conversion actually needs

Slab is the limiting factor 80% of the time — we core-sample, then decide whether to topping-slab or tear-and-pour.

Standard scope · what's in the price

Lift + thermal-image existing slab to assess vapor drive and crack pattern.
Install 10-mil retarder + 2" rigid (R-10) + new 4" topping slab if R-value can't otherwise be met.
Frame interior walls 2×6 @16" o.c., R-21 cavity + R-5 c.i. on exterior face.
New header at former overhead-door opening, brace pack per engineer.
Mini-split heat pump (Mitsubishi / Daikin) on dedicated circuit.
WSEC-compliant whole-house ventilation tied to bath fan.

Code references we work to

IRC R302.6: Garage-to-dwelling separation must be removed when occupancy changes — full thermal & fire-rated assembly.
WSEC R402.2.10: Slab-on-grade in heated space requires R-10 perimeter insulation to 24" below grade or full under-slab.
IRC R310 / R311: New habitable space requires emergency escape opening and code-compliant egress door.

KNOWLEDGE_CENTER / GARAGE CONV.

In-depth guides on garage conv.

Browse the full Knowledge Center →

FAQ

Frequently asked

What is included in GARAGE CONV.?
Our GARAGE CONV. scope includes design through completion: feasibility, schematic design, construction documents, permit submittal and review management, construction with one self-performed framing crew plus L&I-licensed MEP subcontractors, all required WA inspections, certificate of occupancy, and warranty. One contract, one license number, one warranty — not a coordination headache across five vendors.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
How is GARAGE CONV. different from a generic remodel?
GARAGE CONV. carries code, permit, and construction details that a one-off remodeler hasn't repeated enough times to optimize. Examples: IECC R406 envelope path selection, fire separation when units are within 5 ft, side-sewer slope requirements, IRC Appendix AQ when permitted as a tiny house, separate utility metering rules. We do this scope every month — repetition is what makes our first-cycle approval rate and our schedule reliability stand out.
What is the typical price range for GARAGE CONV.?
GARAGE CONV. pricing in 2026 lands $330–$380/sqft all-in depending on size, lot conditions, finish tier, and AHJ. The wide range is real — small lots with difficult access, soils requiring pier-and-beam, or service upgrades push the upper end; flat lots with good access and a catalog plan land at the lower end. Our feasibility report gives you a ±15% number tailored to your specific lot in two weeks.
Go deeper: Seattle ADU cost breakdown
What permits does GARAGE CONV. require?
Standard GARAGE CONV. permit stack: building permit (covers structural, mechanical, plumbing under combined review), side-sewer permit, water meter capacity check, electrical permit, drainage review where applicable, addressing application. Critical-areas review triggers on lots mapped for steep slope, wetland, riparian, or landslide hazard. We pull all permits as a pass-through line in our contract — not marked up.
Go deeper: Read the King County side sewer permits for ADUs: cost & timeline (2026) guide
How long does GARAGE CONV. take from contract to completion?
9–14 months end-to-end is typical for GARAGE CONV.: 6–8 weeks design, 8–16 weeks permit, 18–26 weeks construction. Faster on catalog plans with pre-app meetings. Schedule variance is driven by AHJ workload, owner selection pace, and any field-discovered conditions. We publish a Gantt at contract and update it weekly.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
What's the warranty on GARAGE CONV.?
One year workmanship, two years mechanical (HVAC, plumbing rough, electrical rough), 10 years structural per RCW 4.16.310. Manufacturer warranties pass through directly: LP SmartSide siding 50-year, GAF Timberline HDZ shingles, Marvin window 20-year, Bosch/GE appliances 1-year. Documented in a written warranty packet at closeout.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
Do you self-perform GARAGE CONV. work or subcontract everything?
We self-perform framing, exterior weather barrier, interior trim, and project supervision with W-2 carpenters. MEP trades (plumbing, electrical, HVAC) are subcontracted to L&I-licensed specialty contractors we've worked with 5+ years — WA requires separate PL, EL, HVAC/R licenses that a GC cannot legally self-perform without them.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
What's the change-order policy on GARAGE CONV.?
Every change order is written, priced, and signed before work proceeds. We never charge T&M without a not-to-exceed. Owner-initiated changes carry 15% OH&P; field-discovered conditions (rotted sheathing, undocumented buried oil tank, unmapped sewer) are priced at cost +10% with photo documentation. Average GARAGE CONV. project sees 4–7 change orders totaling 3–6% of contract value.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
What financing works for GARAGE CONV.?
HELOC (fastest, 8.0–9.5% APR), renovation loan (Fannie HomeStyle / Freddie CHOICERenovation, 7.1–7.9%), construction-to-perm (best for ground-up), or cash-out refi (only if existing rate above market). WSHFC's ADU pilot at ~3.5–4.25% applies to ADU-scoped GARAGE CONV. projects for income-qualified owners.
Go deeper: Seattle ADU financing options
Do you provide references for GARAGE CONV. work?
Yes — we provide 5+ GARAGE CONV. references on request: past clients in your target city, your target neighborhood when possible, and at your target scope. References include name, phone, project address, and a one-paragraph project summary. We refresh the reference list quarterly so the contacts are recent and reachable.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide