Building an ADU in San Luis Obispo
What the City of San Luis Obispo and California law let you build: backyard cottages, garage conversions and junior units. Covers sizes, parking, renting, fees and the permit process, with every rule linked to its source.
The short version
| Allowed where | Most lots with a home, including R-1 single-family lots |
|---|---|
| ADU size | 150–850 sq ft (studio/1 bed) · up to 1,000 sq ft (2+ beds) · up to 1,200 sq ft with Director approval |
| Junior ADU (JADU) | Up to 500 sq ft, inside the walls of the main house |
| Detached height | 16 ft (18 ft on some multifamily lots) |
| Side & rear setbacks | 4 ft for new ADUs · none for conversions of existing space |
| Parking | None required, even for garage conversions |
| Renting | 30 days minimum · no Airbnb or homestay |
| Impact fees | None for ADUs of 750 sq ft or less of interior living space |
| City decision | Within 60 days of a complete application, with no public hearing |
Rules for the City of San Luis Obispo. If you're outside city limits, see county rules below.
ADU vs. JADU: what's the difference?
An accessory dwelling unit (ADU) is a complete second home on your lot, with its own kitchen, bathroom and entrance. It can be a detached backyard cottage, an addition attached to your house, or a conversion of existing space like a garage.
A junior accessory dwelling unit (JADU) is smaller, up to 500 square feet, and must be carved out of space inside your existing or new main house. It needs its own exterior entrance and an efficiency kitchen with cooking appliances, a prep counter and storage. It can share a bathroom with the main house. A deed restriction must be recorded before the city issues the permit. [City code]
How many units can you add?
On a single-family lot, the city allows one ADU. You can add a JADU as well if any one of these is true: the ADU is built at the same time as the house; the ADU is a conversion of existing space; or the ADU is detached, no larger than 800 square feet, no taller than 16 feet, and at least 4 feet from the side and rear lot lines. [City code]
State law sets the floor for what every California city must approve. On a single-family lot that includes one ADU plus one JADU inside the house, and one new detached ADU of up to 800 square feet with 4-foot setbacks. SB 543, effective January 1, 2026, confirmed that these can be combined. [Gov. Code §66323] [2025 bills]
On a multifamily lot, state law requires cities to allow ADUs converted from non-living space like storage rooms and garages (at least one, and up to 25% of the existing units), plus detached ADUs: up to eight on a lot with existing apartments, but no more than the number of existing units. [Gov. Code §66323]
Tip: the city and state rules overlap. If a combination you want isn't clearly allowed by the city code, ask City Planning whether state law requires them to approve it. It often does.
Size, height and setbacks
| Standard | City of San Luis Obispo rule |
|---|---|
| Minimum size | 150 sq ft |
| Maximum size, studio or 1 bedroom | 850 sq ft |
| Maximum size, 2+ bedrooms | 1,000 sq ft |
| Director exception | Up to 1,200 sq ft; in R-1 the lot must be at least 12,000 sq ft |
| JADU | Up to 500 sq ft |
| Detached ADU height | 16 ft; 18 ft on a lot with a multifamily, multistory building |
| Attached ADU height | 4-ft setbacks apply to attached ADUs up to 25 ft tall; otherwise the zone's standards apply |
| Side and rear setbacks | 4 ft for new ADUs; none for ADUs in existing structures |
| Front setback | Same as the underlying zone |
Source: SLO Municipal Code §17.86.020. As of 2026, state law measures ADU size by interior livable space (SB 543).
Parking
None. The city requires no additional parking for an ADU or JADU, and if you convert a garage into an ADU you don't have to replace the lost spaces. [City code]
Renting it out
- 30-day minimum. ADUs and JADUs in the city can't be rented for less than 30 days, and homestay use of an ADU is prohibited. [City code]
- No owner-occupancy for ADUs. You can rent an ADU whether or not you live on the property.
- JADU owner-occupancy is in flux. The city code requires the owner to live in the main house or the JADU. AB 1154, effective January 1, 2026, narrowed the state requirement so it applies only when the JADU shares a bathroom with the main house. Ask City Planning which rule applies before you plan around it. [2025 bills]
Fees
- Impact fees: none for an ADU with 750 sq ft or less of interior livable space, and none for a JADU. Larger ADUs can only be charged impact fees in proportion to the size of the main home. [SB 543]
- School fees: starting in 2026, ADUs and JADUs under 500 sq ft of interior livable space are exempt. Larger units can be charged by the school district. [2025 bills]
- Permit fees: building permit and plan check fees still apply. Get a current estimate from the City's Community Development Department.
Budget tip: 750 sq ft is a meaningful line. Staying at or under it avoids impact fees, and a two-bedroom layout fits in that size.
The permit process
- Check your lot. Confirm your zoning and whether you're in city limits, the coastal zone or a fire hazard severity zone.
- Design to the objective standards. Size, height, setbacks and the JADU requirements above.
- Submit to the City. Under SB 543 the city has 15 business days to tell you whether your application is complete, and to list anything missing. [SB 543]
- Approval. ADUs are approved ministerially, with no public hearing. The city must approve or deny within 60 days of a complete application. [City code]
- Build and final inspection. JADUs also need their deed restriction recorded before the permit is issued.
Fire safety: a firefighter's notes
Sprinklers: an ADU or JADU doesn't need fire sprinklers unless the main house is required to have them. [City code]
Fire hazard zones: parts of SLO and much of the county sit in state fire hazard severity zones. New construction there may have to meet California's wildfire building standards, such as ember-resistant vents, ignition-resistant siding and decking, and fire-rated roofing. Look up your address before you design, because it affects materials and cost. [CAL FIRE / State Fire Marshal]
Access: a backyard ADU should have a clear, lit path from the street that a crew can find at night with a hose line. Put the ADU's address number where it's visible from the street. Minutes matter when we're hunting for a unit behind a house.
Selling an ADU separately
Generally not allowed. The city code doesn't allow a subdivision that separates an ADU from the main home "except as provided in state law," and a JADU can never be sold separately. State law (AB 1033) lets cities opt in to allowing ADUs to be sold as condominiums. Check with the City before counting on that option. [City code]
Outside city limits: county rules
If your property is in unincorporated San Luis Obispo County (Los Osos, Nipomo, Templeton, Avila Beach, Cambria and other communities), the County's rules apply instead. The County offers pre-reviewed ADU plans that can speed up permitting for single-family lots in unincorporated areas; the plans can't be modified. See the County ADU page. Cities like Paso Robles, Atascadero, Arroyo Grande, Pismo Beach, Grover Beach and Morro Bay each have their own ADU ordinances.
Common questions
Can I build an ADU in San Luis Obispo?
Yes, on most lots with an existing or proposed home, including R-1 single-family lots. The City of San Luis Obispo must approve an ADU that meets the objective standards in its code, without a public hearing, within 60 days of a complete application.
How big can an ADU be in San Luis Obispo?
Up to 850 square feet for a studio or one-bedroom and up to 1,000 square feet for two or more bedrooms. The Community Development Director can approve up to 1,200 square feet; in the R-1 zone that exception requires a lot of at least 12,000 square feet. A junior ADU (JADU) is capped at 500 square feet.
Do I need extra parking for an ADU in SLO?
No. The city code says no additional parking spaces are required for an ADU or JADU, and converting a garage into an ADU does not require replacement parking.
Can I rent my ADU on Airbnb in San Luis Obispo?
No. ADUs and JADUs in the city cannot be rented for less than 30 days, and homestay use of an ADU is prohibited.
Do I have to live on the property to build an ADU?
Not for an ADU. For a JADU, the city code requires the owner to live in the main house or the JADU. Under AB 1154, effective January 1, 2026, state law requires owner-occupancy only when the JADU shares a bathroom with the main house, so confirm with City Planning which rule the city is applying.
What fees do ADUs pay in San Luis Obispo?
Under state law, ADUs with 750 square feet or less of interior livable space are exempt from development impact fees, and larger ADUs can only be charged in proportion to the size of the main home. ADUs and JADUs under 500 square feet of interior livable space are also exempt from school fees. Building permit and plan check fees still apply.
Can I sell my ADU separately from my house?
Generally no. The city code does not allow a subdivision that separates an ADU from the main home, except where state law allows it, and a JADU can never be sold separately from the main house.
Sources
- San Luis Obispo Municipal Code §17.86.020 (ADUs and JADUs)
- California Government Code §66323 (ADU combinations the city must approve)
- California HCD: Accessory Dwelling Units and ADU Handbook
- SB 543 (2025): ADU fees, measurement and permit timelines
- Summary of 2025 ADU bills (SB 543, AB 1154, AB 462, SB 9)
- City of San Luis Obispo Planning & Zoning
- County of San Luis Obispo: Accessory Dwelling Units
- County of San Luis Obispo: Pre-reviewed ADU plans
- CAL FIRE / State Fire Marshal: Fire Hazard Severity Zones
This guide is general information, not legal or permitting advice. ADU law changes often. Confirm your project with the City of San Luis Obispo Community Development Department before you design or buy. Last reviewed September 22, 2026.