How to Build an ADU in Los Angeles: A Step-by-Step Guide for Homeowners

Why Los Angeles Homeowners Are Racing to Build ADUs

Accessory dwelling units have become one of the most talked-about construction projects across Los Angeles County. Rising rents, multigenerational living needs, and state-level legislation that streamlined ADU approvals have converged to make backyard cottages, garage conversions, and junior ADUs an attractive option for homeowners who want to maximize their property's value without selling. Whether your goal is rental income, housing an aging parent, or creating a private home office, understanding the full process before you break ground is essential.

At ADU Builders & Foundation Repairs, we manage every phase of the ADU journey for Los Angeles homeowners, from the first site visit through the certificate of occupancy. Below, we break down exactly what you can expect.

Step 1: Assess Your Property's ADU Potential

Not every lot is immediately ready for an ADU, but Los Angeles zoning changes have made it possible for the vast majority of single-family and multi-family properties to add at least one unit. During your initial site assessment, a contractor will evaluate the following:

• Lot size and setbacks — State law generally allows ADUs up to 800 sq ft regardless of lot coverage limits, but larger units require meeting rear and side setbacks (typically 4 feet).
• Existing utilities — Water, sewer, and electrical capacity must support the new unit. In some cases, a service upgrade or separate meter is required.
• Foundation conditions — If you are converting a garage or adding a detached structure, the existing slab or soil conditions must be evaluated. Our foundation repair and retrofitting team can assess whether any structural work is needed before ADU construction begins.
• Garage or existing structure — A detached garage is often the fastest path to an ADU because the footprint, slab, and roof structure already exist.

Step 2: Choose Your ADU Type

Los Angeles recognizes several ADU categories, and the right choice depends on your goals, budget, and property layout:

• Detached ADU — A freestanding structure in the backyard, offering maximum privacy for tenants or family members.
• Attached ADU — Built as an addition connected to the main house, sharing at least one wall.
• Garage conversion ADU — Converting an existing attached or detached garage into living space, often the most cost-efficient option.
• Junior ADU (JADU) — Carved from existing interior square footage, capped at 500 sq ft, and typically faster to permit.

If you are also considering expanding your home's primary footprint, our room addition services can be bundled with an ADU project to reduce overall mobilization costs.

Step 3: Architectural Design and Engineering

Once you have selected an ADU type, the design phase begins. Your contractor or design team will prepare architectural drawings that reflect your unit's layout, exterior materials, window placement, and roofline. For detached ADUs and any project involving a new foundation, a licensed structural engineer must stamp the plans. These stamped drawings are required for permit submission to the Los Angeles Department of Building and Safety (LADBS).

Design decisions made at this stage — ceiling heights, kitchen layout, bathroom placement, natural light sources — directly affect your long-term rental appeal and livability, so it pays to be thorough before the plans are finalized.

Step 4: Permit Submission and Approval

All ADUs in Los Angeles require permits. The permit set typically includes building, electrical, plumbing, and mechanical permits. For standard detached ADUs, the LA Department of Building and Safety offers a pre-approved standard plan program that can significantly reduce plan-check review time. Custom designs go through a standard plan check, which can take several weeks to a few months depending on complexity and current LADBS workload.

Our team handles the complete permit application process on behalf of homeowners throughout Los Angeles and surrounding communities including Montebello, Alhambra, and Monterey Park. We respond to any plan-check corrections promptly to keep your timeline on track.

Step 5: Construction Phases

Once permits are in hand, construction moves through a well-defined sequence:

• Site preparation and foundation work — Grading, excavation, formwork, and concrete pours for footings and slabs.
• Framing — Wall framing, roof framing, and sheathing bring the structure to life.
• Rough mechanical, electrical, and plumbing — Trades install systems inside the walls before they are closed up; city inspections occur at this stage.
• Insulation and drywall — Walls and ceilings are insulated to meet California Title 24 energy standards, then drywalled and textured.
• Interior finishes — Flooring, cabinetry, countertops, tile, fixtures, and appliances are installed.
• Final inspection and certificate of occupancy — A city inspector signs off on all systems and issues the CO, making the unit legally habitable and rentable.

Step 6: Timeline and Cost Expectations

A detached ADU in Los Angeles typically takes 4 to 6 months from permit approval to move-in. Garage conversions can be completed in 3 to 4 months. Permit processing adds additional time on the front end — often 2 to 4 months for a standard plan check, though pre-approved plans can compress that window considerably. Budget-wise, ADU construction in Los Angeles generally ranges from $150,000 to $350,000 depending on size, finish level, and site conditions.

Ready to Start Your ADU Project?

Adding an ADU is one of the smartest property investments available to Los Angeles homeowners today. Our team at ADU Builders & Foundation Repairs is ready to walk you through a site assessment and produce an honest cost estimate with no pressure. We serve homeowners across East Los Angeles, Glendale, South Gate, and the broader LA metro area.

Learn more about our ADU Construction & Design services or call us at (213) 583-5800 to schedule your consultation. Our team is available Monday through Sunday, 8:00 AM to 6:00 PM.