Hercules, CA Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Hercules, CA, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Setback requirement
- Only enough for fire/safety
- Garage door
- Must be replaced with rated wall/window/door
- Replacement parking
- Not required after conversion
- Fee exemption
- If unit stays under 750 sq ft
- Fire Marshal review
- Required for door/window features
Summary
Converting a Hercules garage into an ADU is allowed with no setback or design-review hurdles beyond fire safety, but the garage doors must be replaced with code-rated walls, windows, or doors built for habitable space.
ADUs Within Existing Space. An ADU within existing space and a JADU within existing space are permitted as long as the side and rear setbacks are sufficient for fire and safety... Garage spaces converted to ADUs shall replace garage doors with walls, windows, and/or doors rated by building code for habitable spaces.
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 555, passed March 25, 2025).
Full Breakdown
320(5)(A) governs ADUs built within existing space, including converted garages, and sets minimal standards: side and rear setbacks need only be sufficient for fire and safety, and no other development standard in the section applies except two carve-outs. First, only one ADU within existing space and one JADU within existing space are allowed per lot, unless the owner separately obtains permits for multiple ADUs under the multifamily provisions of subsection (10)(A)(4). Second, and specific to garages, subsection (5)(A)(2) requires that 'garage spaces converted to ADUs shall replace garage doors with walls, windows, and/or doors rated by building code for habitable spaces,' converting the opening into a code-compliant exterior wall rather than leaving a garage door in place.
Subsection (6) adds that when an existing garage is converted, window and door features may be required for consistency with fire and building codes, in consultation with the Fire Marshal, and the finished unit must match the architectural features, materials, and paint color of the existing residence. Subsection (9) separately confirms that when a garage is demolished or converted for an ADU, the City does not require replacement parking for the space that was lost, removing what is otherwise the biggest parking obstacle to garage conversions.
Because a garage-converted ADU is treated as 'within existing space,' it also qualifies for the fee exemption in subsection (4)(B)(2) if it stays under 750 square feet.
Violations & Fines
Garage conversions performed without a building permit, or that leave the garage door in place instead of installing code-rated walls, doors, or windows as subsection (5)(A)(2) requires, are Municipal Code violations subject to the citywide default in Section 1-4.01: a misdemeanor punishable by up to a $1,000 fine, up to six months' imprisonment, or both, with continuing violations counted daily. The City may also require the Fire Marshal to review the conversion before final sign-off.
Frequently Asked Questions
Do I need to keep the garage door if I convert my garage to an ADU in Hercules?
Will I have to build new parking to replace the garage I converted?
Are there setback requirements for a garage-converted ADU?
Sources & Official References
Other rules in Hercules
California rules heatmap·Compare Hercules to another location·View the California accessory structures overview
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Garage Conversions in Nearby Cities
How other cities in Contra Costa County handle garage conversions.