ADU Construction in Los Angeles in Santa Monica
Serving 90401 · 90402 · 90403 · 90404 · 90405 and Venice, Brentwood, Pacific Palisades
California's ADU laws have made backyard units one of the highest-leverage property improvements an LA homeowner can make. We design and build all three types — detached new builds, attached additions, and JADUs (Junior ADUs converted from existing space). End to end. Permits, plans, foundations, framing, finishes, and final inspections, all under one roof. You work directly with Onn from feasibility study through certificate of occupancy.
ADU Construction in Los Angeles specifically for Santa Monica
Every neighborhood has its own architectural character, permit jurisdiction, and finish-level expectations. Here's how we approach adu construction in los angeles in Santa Monica specifically.
Coastal climate adjustments
Salt air degrades standard hardware and cabinet hinges within a few years. We spec marine-grade or coated hardware for Santa Monica projects — small upcharge, big longevity gain.
Santa Monica permit & code
Santa Monica has its own building department, generally well-organized but slow during peak season. Coastal Commission review can apply for properties west of Lincoln Blvd in some cases.
Tenant-occupied projects
If your property has tenants under rent stabilization, scope and timing have legal implications. We coordinate with your tenants and (when needed) your attorney to keep projects compliant.
What we handle
Feasibility & site planning
Lot review, setbacks, height limits, utility access, soil assessment. We tell you up front whether your project pencils — square footage, code constraints, expected timeline.
Architectural design
Floor plans, elevations, 3D renderings. We design to maximize functional space within California's ADU size limits (up to 1,200 sq ft detached, 850 sq ft for studios/1-bedroom).
Permits & utilities
Plan check submission, energy compliance (Title 24), structural engineering, separate or shared utility service. We deal with LADBS or your municipal building department.
Foundation, framing, finish
New foundations or attached construction, framing, MEP rough-in, exterior, and full interior finishes — kitchen, bath, flooring, HVAC, electrical.
Final inspection & C of O
Final inspections, Certificate of Occupancy, and walkthrough. We hand you a unit you can live in, rent, or use as a guest house.
Pricing in Santa Monica
Typical detached ADU build cost in Los Angeles, all-in (design, permits, construction, finishes, utility hookups). Attached ADUs typically run lower; JADUs converting existing space lower still.
City of Santa Monica Building & Safety. Coastal Commission review may apply for properties near the bluffs or west of Lincoln. Plan check typically 4–8 weeks.
Frequently asked
How big can my ADU be in Los Angeles? +
California state law allows detached ADUs up to 1,200 sq ft (or larger if your local jurisdiction permits). Attached ADUs are limited to 50% of the primary home's square footage or 1,200 sq ft, whichever is less. Junior ADUs (JADUs) are capped at 500 sq ft and must be inside the existing primary structure.
How long does an ADU project take? +
Plan to design and build a detached ADU in 9–14 months total: 2–3 months for design and permits, 6–10 months for construction. Attached ADUs and JADU conversions can run shorter.
Do you work in 90402 (north of Montana)? +
Yes. North of Montana has some of the area's highest-end remodels and we've done full-home projects there.
Salt-air resistance — how do you handle it? +
Marine-grade or PVD-coated hardware on visible fixtures, stainless cabinet hinges, and corrosion-resistant fasteners on exterior work. Adds a few percent to material cost.
From the blog
ADU vs Garage Conversion: Which Makes Sense for Your LA Property?
A clear-eyed comparison of detached ADUs, attached ADUs, JADUs, and garage conversions for LA homeowners — costs, timelines, ROI, and which one fits your lot.
LA County Kitchen Permits Explained (2026 Edition)
When you actually need a permit for a kitchen remodel in Los Angeles, how the plan-check process works, typical timelines for LADBS and surrounding cities, and how to avoid the common mistakes.
ADU Construction in Los Angeles in other neighborhoods
Live in Santa Monica?
Onn personally reviews every inquiry. Tell us about your project — Onn will be in touch within one business day.