Boulder County, CO Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Boulder County, CO, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Permit
- Building permit required
- Second-floor unit
- Treated as accessory dwelling
- Counts toward
- Parcel Residential Floor Area
- Wastewater
- May need larger OWTS
- Governing code
- BCLUC Articles 4-405 & 4-516
Summary
Converting a garage into living space, or into an accessory dwelling, requires a building permit and must comply with the Boulder County Land Use Code. A detached garage designed with habitable space (such as a second-floor unit) is treated as an accessory dwelling and counts toward the parcel's Residential Floor
Accessory Dwelling Units (including detached garages designed with Habitable Space on the second floor) must meet the above requirements of 4-405(C)(2) for residential buildings.
Full Breakdown
There is no separate 'garage conversion' section in the Land Use Code; a conversion is regulated as either added Residential Floor Area or a new accessory dwelling. The BCLUC expressly treats a detached garage designed with habitable space (for example, living quarters on the second floor) as an Accessory Dwelling Unit that must meet the county's residential building and floodplain standards. Converting an attached or detached garage to a bedroom, office, or apartment therefore requires a building permit, may require added onsite wastewater capacity (CDPHE Reg 43), and must stay within the parcel's maximum Residential Floor Area. In floodplain areas, converted space below the flood protection elevation faces additional restrictions.
Violations & Fines
Occupying a converted garage as living space without permits is a zoning and building code violation; the county may order the space returned to non-habitable use or bring enforcement and fines under Article 4-1300.
Frequently Asked Questions
Is converting my garage to a bedroom allowed?
Does an apartment over my garage count as an ADU?
Sources & Official References
Other rules in Boulder County
Compare Boulder County to another location·View the Colorado accessory structures overview
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