A garage conversion is usually the lowest-cost path to an ADU in Boulder — $100,000-$250,000, versus $200,000-$450,000 for a new detached build — because the shell already exists.
Garage Conversion Cost in Boulder
Converting an existing garage in Boulder runs $100,000-$250,000. That's well under the $200,000-$450,000 typical cost of a ground-up detached ADU, because you're reusing the foundation, walls, and roof. The biggest variables are whether the slab and framing are sound, what utility/electrical upgrades are needed, and your finish level. Permit fees add Valuation-based (2026 schedule): $1,059 + $5.95 per $1,000 over $100,000, plus 25% plan check and $83.90 energy fee: about $1,700 for an 800 sq ft unit at the city's $170.80/sq ft floor, about $2,900 on a $300,000 contract. Use tax, trade permits, impact fees and excise tax are extra.. A converted unit rents for about $1,900-$2,400/mo (1BR) in Boulder.
The Boulder Garage Conversion Permit Process
A garage-to-ADU conversion in Boulder needs building permits even if the exterior is unchanged. Approval process: Building permit only: since Sept. 1, 2023 (Ord. 8571) there is no separate ADU or administrative review. Apply in the Customer Self-Service Portal with the ADU Application Form, stamped plans by a licensed design professional, the roof pitch (detached) or lockable separation and house floor plans (attached). Detached units need an automatic fire sprinkler on a bypass meter and an In-Property Wet Utility Permit; affordable ADUs record a Declaration of Use; lots under an old PUD or site review need a minor modification first. The review timeline is Not fixed. P&DS posts 6 business days for the completeness check, then 7 weeks of review for new construction (4 weeks for other scopes) and 'full review up to 9 weeks' (Sept. 2026); a permit application expires after 180 days without progress., with plan check: 25% of the building permit fee for single-family residential, paid at application and nonrefundable (2026 schedule, Sec. 4-20-4(f)7); the completeness check and plan-check invoice take about 6 business days.. Pre-approved plans: None. The city publishes no pre-approved ADU plan set (Sept. 2026); the ADU Guide only lists the required drawings and forms..
- Confirm eligibility — ADUs are allowed in By right on a lot with one detached house in every residential district (RR-1, RR-2, RE, RL-1, RL-2, RM-1/2/3, RMX-1/2, RH-1/2/3/7), the MU-1 to MU-4, BT, BC, BR and DT-1 to DT-5 business and downtown districts, IG, A and P (Table 6-1 as amended by Ord. 8650; use standards in BRC 9-6-3(n)). Not allowed in RH-6, MH, BMS, BCS or IS-1 (the ADU Guide also excludes IM), on a lot without a single detached dwelling, or on a home with a permanent affordability deed restriction..
- Prepare conversion plans — layout, egress windows, insulation, ventilation, smoke/CO detectors, plus a kitchen and bathroom.
- Submit for plan check — 25% of the building permit fee for single-family residential, paid at application and nonrefundable (2026 schedule, Sec. 4-20-4(f)7); the completeness check and plan-check invoice take about 6 business days..
- Pull permits and build — fees run Valuation-based (2026 schedule): $1,059 + $5.95 per $1,000 over $100,000, plus 25% plan check and $83.90 energy fee: about $1,700 for an 800 sq ft unit at the city's $170.80/sq ft floor, about $2,900 on a $300,000 contract. Use tax, trade permits, impact fees and excise tax are extra.; then framing, electrical, plumbing, and final inspection.
Parking Rules for a Garage Conversion
None for the ADU. Ord. 8650 (effective March 8, 2025) struck the ADU parking table from 9-6-3(n) and set the Table 9-2 requirement for attached and detached ADUs to 0; the main house keeps whatever its district requires. This is Boulder's own rule: C.R.S. 29-35-103 (HB 24-1152) only bars requiring a new space and lets a city designate an existing one. Garage conversions sometimes trigger different parking rules than new detached ADUs, so confirm replacement-parking requirements with Boulder before you start. Owner-occupancy is not required, so you can rent the converted unit out.
The JADU Option for an Attached Garage
If your garage is attached to the house, you can convert it into a junior ADU (JADU) — capped at Boulder has no junior ADU category. A unit inside the house is an attached ADU under 9-6-3(n)(2): it must be separated from the main home by a wall or lockable door, and any existing interior connection must be kept. and built within the existing walls. JADUs are cheaper and faster to permit than a full ADU, though they may share sanitation with the main home. A full ADU gives you more size and a separate unit; a JADU is the budget route.
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Boulder Garage Conversion FAQ
How much does a garage conversion cost in Boulder?
Do I need a permit to convert a garage in Boulder?
Do I have to replace the parking if I convert my garage in Boulder?
How long does a garage conversion take in Boulder?
Can I convert an attached garage into a JADU in Boulder?
Compare your options: see the full Boulder ADU rules, estimate your build with the Boulder ADU cost calculator, or read the general garage conversion guide.