What is a casita? Casita vs ADU vs guest house in California

What is a casita?

Casita is the Spanish diminutive of casa, house. Dictionary.com defines it as a small house, especially one built alongside or as an addition to a larger main home, and notes the word is especially common in the Southwest. In California real estate it's a friendly name for a backyard cottage, a guest house or a granny flat, often in a Spanish or Mission style that matches the main house.

Planners treat it as one more name for an ADU. California's housing department says ADUs have been known by many names, including granny flats, in-law units and backyard cottages, and the Association of Bay Area Governments adds “casitas” to that list. Our guide to granny flat vs ADU sorts out the rest of the nicknames, and what an ADU is covers the basics.

Casita vs ADU vs guest house

When you apply for a permit, your casita has to be one of the categories the code recognizes. State law defines an ADU as a unit with complete independent living facilities, including permanent provisions for living, sleeping, eating, cooking and sanitation. That's the line: a casita with a kitchen is an ADU.

The ADU rows come from San Diego Municipal Code § 141.0302; guest quarters from § 141.0307 in the same division; junior ADUs from Government Code § 66333. The city's guest quarters rule says the building “shall not contain a kitchen or facilities for the storage and preparation of food,” though a bar sink and a miniature refrigerator may be permitted, and the quarters can't be rented. In unincorporated areas, the County's guest living quarters rules also bar kitchens, wet bars and laundry.

For a backyard unit you'll rent or live in full-time, building it as an ADU nearly always wins. We cover the trade-off in detail in guest house vs ADU.

Casita permits in San Diego

A casita built as an ADU gets the state's ADU protections. A city must review it ministerially, with no hearing, and approve or deny within 60 days of a complete application. Every city must approve a detached ADU of up to 800 sq ft with 4-foot side and rear setbacks.

Rules from the city's ADU code; the fee exemption from SDMC § 142.0640. Guest quarters take a different path: they're a limited use under § 141.0307, and before the building permit is issued the owner must sign and record a Habitable Accessory Structure Agreement promising not to sell the two buildings separately. The city's ADU bulletin says guest quarters are allowed in addition to ADUs. Step-by-step instructions are in our ADU permit guide for San Diego, and the state rules are in California ADU laws.

How much a casita costs

A casita costs what an ADU of the same size costs. Snap ADU's published San Diego prices (March 2026) put a detached 500 sq ft ADU at about $300,000 and a 750 sq ft unit at about $350,000. Its guest house guide puts a detached guest house at $300,000 to $500,000 all-in, or about $375 to $600 per square foot. Dropping the kitchen saves cabinets and appliances, but the foundation, framing, bathroom and utilities stay.

Figures from Snap ADU, Lars Remodel's cost guide and Snap ADU's fee table; they're builder estimates, not quotes. Snap's base prices include design, permit management and about $35,000 of level-lot site work, but not fees, demolition or retaining walls. Put your own numbers into our ADU cost calculator, or see what an ADU costs in San Diego for the full breakdown.

Casita design styles

“Casita” suggests a look as much as a use. These are the styles you'll see most around San Diego. None is required by code; they're choices your designer can draw on any ADU plan.

• Spanish Colonial and Mission. Smooth stucco walls, a low-pitched clay tile roof, arched openings and wood beams. Clay tile is heavy, so it shapes the roof framing and the budget.
• Hacienda courtyard. The casita sits across a patio or courtyard from the main house, so the outdoor space works as a shared room. Good for family, harder to make private for a tenant.
• Modern Spanish. Stucco and tile accents with larger windows, cleaner lines and a flat or shallow roof, which also helps keep a single-story unit low.
• Desert or Santa Fe. Flat roof, rounded parapets and earth-tone stucco.
• Matching the house. Many owners simply repeat the main home's siding, roof and trim so the casita reads as part of the property.

For layouts at each size, start with ADU floor plans or the County of San Diego's free plan sets. If you're in a high fire hazard area, materials rules apply; see ADUs in fire zones. More inspiration is in ADU design ideas.

Buying a house with a casita

Listings for a house with a casita don't always say whether the casita was permitted, or permitted as what. Before you count on rental income:

• Pull the permit history. Confirm the casita was permitted as an ADU, not as guest quarters, a workshop or nothing at all. A recorded Habitable Accessory Structure Agreement on title is a sign it was permitted as guest quarters.
• Look at the kitchen. A kitchen in a building permitted as guest quarters is a violation, not a rentable unit.
• Ask about legalizing. The City of San Diego has a path for legalizing unpermitted ADUs, and state law limits when a city can deny a permit for an older unpermitted unit. Our guide to unpermitted ADUs in California explains the process.

See buying a home with an ADU for the full checklist. If you're building rather than buying, compare verified ADU builders in San Diego or our list of the best ADU builders in San Diego, then check a contractor's license and read how to hire an ADU contractor.

Common questions