What an ADU actually costs in Los Angeles
Across Los Angeles, the all-in cost of a permitted ADU in 2026 typically ranges from about $180,000 for a modest garage conversion to well over $450,000 for a fully custom 1,200-square-foot detached unit. That spread is wide because the term 'ADU cost' bundles together very different work — design, plans, permits, demolition, foundation, framing, MEP (mechanical, electrical, plumbing), finishes, landscaping restoration, and utility upgrades. Understanding which line items drive your number is the difference between a project that pencils out and one that surprises you mid-construction.
The four cost drivers that matter most
First, size: every additional 100 square feet adds roughly $25,000–$40,000 depending on finish level. Second, type: a garage conversion reuses an existing slab and walls, while a detached ADU requires a fresh foundation, full envelope, and new utility runs — typically a 25–40% premium per square foot. Third, utilities: if your existing electrical panel can't accept the additional load, a service upgrade alone can add $8,000–$15,000. Fourth, site conditions: hillside lots, narrow access, mature trees, and existing hardscape removal all add cost.
Soft costs you should budget for
Architectural design and structural engineering typically run 8–12% of construction cost. City permit fees in LA range from a few thousand dollars for a JADU up to $15,000+ for a larger detached ADU once school fees, plan check, and impact fees are included. Add a contingency of 8–10% for unforeseen site conditions — older homes in LA frequently surface knob-and-tube wiring, asbestos, or undersized water lines once walls open up.
How financing changes the math
Many homeowners finance ADU construction through a HELOC, cash-out refinance, or a specialized renovation loan. Because an ADU typically generates $2,000–$5,000/month in rent and adds significant property value, the long-term ROI almost always exceeds the cost of capital — but it's still essential to model debt service against realistic rental income for your specific neighborhood.
Get a real number for your property
Online calculators give you a wide range; only a site visit gives you a real one. AER Builders provides free in-person property assessments throughout Los Angeles, including a feasibility review, ballpark cost, and an honest discussion of whether an ADU makes sense for your specific lot, budget, and goals.