A garage conversion is usually the lowest-cost path to an ADU in Boulder — $80,000-$180,000, versus $160,000-$320,000 for a new detached build — because the shell already exists.
Garage Conversion Cost in Boulder
Converting an existing garage in Boulder runs $80,000-$180,000. That's well under the $160,000-$320,000 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 $1,900-$3,200. A converted unit rents for about $1,600-$2,100/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: Streamlined review process The review timeline is 40-60 days, with plan check: 2-3 weeks. Pre-approved plans: Available.
- Confirm eligibility — ADUs are allowed in All single-family and multi-family zones.
- Prepare conversion plans — layout, egress windows, insulation, ventilation, smoke/CO detectors, plus a kitchen and bathroom.
- Submit for plan check — 2-3 weeks.
- Pull permits and build — fees run $1,900-$3,200; then framing, electrical, plumbing, and final inspection.
Parking Rules for a Garage Conversion
Not required (no parking minimum for ADUs per Ordinance 8650, eff. March 8, 2025; consistent with CO HB24-1152) 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 does not use a separate JADU category 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.