California ADU rules · San Mateo County
Can I Build an ADU in Colma?
Yes — you can build an ADU in Colma. California's statewide ADU law requires every city, including Colma, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
Local rule1 detached new construction ADU + 1 conversion ADU + 1 JADU
Allows up to three accessory units per single-family lot: one detached, one conversion, and one JADU.
Units on a multifamily lot
Local ruleup to 8 detached (or up to number of existing primary units, whichever is less); conversions (>=1 or 25% of units); up to 2 detached on proposed multifamily; JADUs not allowed
Detached ADUs capped at 8 or number of existing units; JADUs prohibited on multifamily lots.
Junior ADU (JADU)
Local ruleAllowed
JADUs allowed only on single-family lots, not on multifamily.
Size & height
Max detached ADU size
CA state law1,200 sq ft
Statewide default cap for detached new-construction ADUs in the absence of a compliant local ADU ordinance. The unconditional by-right floor a city must always allow is 800 sq ft (see Guaranteed minimum size); a city with a compliant ordinance may set its own ceiling.
Max attached ADU size
Local rule50% of primary, >=850 (>=1,000 for 2+ bedrooms)
Attached ADUs further limited to 50% of primary dwelling floor area.
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
Local rule500 sq ft
JADU must be entirely within the primary dwelling or attached garage.
Max height
CA state law16 ft
16 ft baseline; cities must allow 18 ft within ½ mi of a major transit stop or where the primary dwelling is two-story, and 20 ft on a lot with a multistory multifamily building.
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
Local ruleNo more than 19 ft from front property line and 15 ft from street-facing property line; cannot preclude 800 sq ft ADU with 4 ft side/rear setbacks
Front setback rules cannot block a compliant 800 sq ft ADU.
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
Local ruleNone
No parking required for ADUs or JADUs.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
Local ruleNot required
No replacement parking required when parking is removed for ADU/JADU.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
Local rule45 days
45 days for standard ADU/JADU applications; 30 days for pre-approved plan ADUs.
Owner-occupancy
Local ruleOnly for a JADU
Owner-occupancy required only if JADU shares sanitation with primary dwelling.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Colma-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Historic properties
ADUs/JADUs on properties listed in the California Register of Historic Resources must comply with the Secretary of the Interior’s Standards for Rehabilitation.
Colma allows up to three accessory units on single-family lots (detached, conversion, and JADU), prohibits JADUs on multifamily lots, and requires no parking for ADUs or JADUs. Historic properties must meet federal rehabilitation standards.
Frequently asked questions
Can I build an ADU in Colma?
Yes. California's statewide ADU law requires Colma to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Colma?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Colma?
Side and rear setbacks are limited to 4 ft. No more than 19 ft from front property line and 15 ft from street-facing property line; cannot preclude 800 sq ft ADU with 4 ft side/rear setbacks.
Is parking required for an ADU in Colma?
None. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Colma?
A complete application must be acted on within 45 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Colma?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Colma Zoning Code, Chapter 5.03 (Accessory Dwelling Units), last amended March 2026
- Colma Zoning Code § 5.03.110, Table 2
- Colma Zoning Code § 5.03.113(c), Definitions
- Colma Zoning Code § 5.03.111, Table 3
- Colma Zoning Code § 5.03.113(c)
- Colma Zoning Code § 5.03.109, Table 1; § 5.03.111, Table 3
- Colma Zoning Code § 5.03.109, Table 1; § 5.03.105(a)
- Colma Zoning Code § 5.03.105(a)
- Colma Zoning Code § 5.03.104(b)
- Colma Zoning Code § 5.03.113(h)
- Colma Zoning Code § 5.03.112(c)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated March 2026. This is an AI-assisted summary of Colma's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Colma Planning before relying on it.
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