How much does a garage conversion ADU cost in 2025?

Costs vary by city and scope, but garage conversions are usually the lowest-cost ADU path because you’re reusing the shell. Expect ranges that reflect foundation upgrades, new plumbing runs, and egress windows. Use our ranges as a planning baseline, then validate with local bids. {{verify locally}}

Do I need parking replacements when converting a garage?

Many jurisdictions waive replacement parking for ADUs, but rules differ. Check your local ordinance and planning portal before demo. {{verify locally}}

How long does a garage conversion take?

Typical durations: design 4–8 weeks, permits variable, construction 8–16 weeks, depending on utilities and inspections. Allow lead time for panel upgrades and trenching.

Will my slab and walls meet code?

Garages often need foundation thickening at edges, vapor barrier, insulation, and shear/wall upgrades. Your engineer and inspector will define the final scope. {{verify locally}}

Can I finance a garage conversion ADU?

Yes—HELOCs, cash-out refis, and construction loans are common. Compare payment options and draw structures with your lender.

Costs

Garage Conversion ADU (2025): Costs, Permits, Timeline

The most budget-friendly way to add housing—what it really costs, the permit steps to expect, and how to prevent scope creep.

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Quick table of contents

Garage conversions are often the fastest, lowest-cost ADU path because you’re reusing the shell. Plan for slab upgrades, new plumbing and electrical, proper insulation, and egress. Get two apples-to-apples bids and tie payments to inspected milestones.

Typical cost ranges (2025)

Scope	Low	Mid	High
Design & engineering	$6k	$12k	$20k+
Permits & fees	$2k	$5k	$12k+
Slab/foundation upgrades	$3k	$9k	$18k+
Framing/shear & insulation	$6k	$12k	$20k+
Electrical & panel	$4k	$10k	$18k+
Plumbing (new bath/kitchen)	$8k	$18k	$35k+
Windows/egress & door	$3k	$8k	$15k+
Finishes (drywall, flooring, cabinets)	$10k	$25k	$45k+
HVAC (mini-split, ventilation)	$3k	$6k	$12k+
Estimated total	$45k	$95k	$190k+

Numbers vary by city, utility distance, and selections. Treat these as planning placeholders. Always validate with local bids and your city’s fee schedule. {{verify locally}}

320–480 sf
common garage size

8–12 yrs
typical rent payback

10–15%
recommended contingency

Scope checklist (avoid scope creep)

Structural: slab edge thickening, sill plate, shear walls, garage door infill framing.
Envelope: continuous insulation, moisture barrier, air sealing, Title 24/IECC compliance.
Life safety: egress window sizes, smoke/CO, bedroom egress, tempered glazing near doors.
Plumbing: new sewer tie-in, venting, trenching, backflow as required. Camera-scope existing laterals.
Electrical: dedicated circuits, AFCI/GFCI, subpanel or main panel upgrade, exterior lighting.
HVAC: properly sized mini-split and bath fan with continuous ventilation mode.
Sound & comfort: insulation at demising walls, resilient channels if attached.
Finish: cabinets with clear allowances ($/lf), durable flooring, wet-area tile waterproofing.

Pro tip: Ask bidders for an Inclusions & Exclusions exhibit and an Allowance Schedule with unit costs. That single page prevents most cost drift.

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Permit steps (typical)

Feasibility: Confirm zoning, setbacks, parking, utilities on your planning portal. Screenshot requirements. {{verify locally}}
Plans: Hire designer/engineer; include structural notes for slab and wall upgrades; note egress sizes.
Submittal: Apply for building permit; include Title 24/energy forms; pay plan check fees.
Corrections: Respond to comments; update sheets; resubmit.
Construction: Inspections at rough MEP, insulation, drywall, and finals; schedule utility work windows.
Closeout: Final inspection, smoke/CO verification, address assignment if applicable, utility sign-offs.

Timeline & ROI quick math

Typical durations

Design: 4–8 weeks
Permits: variable (plan check + corrections)
Construction: 8–16 weeks

Buffer for panel upgrades, trenching, and special-order windows/doors.

Project cost ($) Expected monthly rent ($) Vacancy/maint. %

Payback ~ 4.6 years (rough). Financing will change this; use our payment calculator next.

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Case study: 420 sf garage → studio ADU

Garage conversion ADU with kitchenette and egress window — Scope included trenching 42 ft for new sewer, panel upgrade to 200A, garage door infill with window, and sound-insulated demising wall.

Primary home with landscaped path to ADU — Owner handled selections early, staying 5% under allowances by choosing in-stock flooring and fixtures.

Results

Construction: 12 weeks; 3 inspection cycles
Total cost: $102k (incl. fees) — contingency used: 9%
Rented in 2 weeks at $1,850/mo; projected payback ~4.9 years

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FAQ

Do I have to replace the lost parking?

Many cities waive replacement parking for ADUs, especially near transit, but not all. Confirm on your city planning portal before removing doors or slab. {{verify locally}}

Can I keep laundry or storage in the converted space?

Most ADUs must be fully habitable space; shared laundry/storage may not count. Ask your planner how they treat accessory uses. {{verify locally}}

Is my existing slab good enough?

Inspect for cracks and edges; many garages need edge thickening, vapor barrier, and anchorage upgrades. Your engineer will specify details. {{verify locally}}

Will I need a separate address and meter?

Addressing and metering policies vary. Some cities allow shared meters; others require separate. Check local utility rules. {{verify locally}}

What if I want a bedroom?

Bedrooms add egress and ventilation requirements. Confirm window sizes and sill heights; consider layouts that preserve parking/clearances if attached. {{verify locally}}

Next steps

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