1. The Bottom Line Up Front
A typical 600 sq ft detached ADU in Los Angeles County costs between $147,000 and $231,000 all-in — from the first permit application to the day you hand over the keys. That range is wide because LA is a wide market: labor costs in Bel Air are not the same as in Gardena, and a hillside lot with a retaining wall is a fundamentally different project than a flat lot in Torrance.
What this article gives you is a real, line-by-line breakdown of where that money goes — not the $80K fantasy numbers you see in some contractor ads, and not the $400K horror stories from people who hired the wrong team. This is what a transparent, well-managed ADU project actually costs in 2026.
Garage Conversion
$60K – $110K
Existing structure, limited permits
Attached ADU
$90K – $160K
Shares walls, combined utilities
Detached ADU
$147K – $231K
600 sq ft, full new construction
2-Story Detached
$200K – $320K
800–1,200 sq ft, premium finishes
2. Cost by ADU Type
The type of ADU you build is the single biggest driver of total cost. Garage conversions are cheapest because the structure already exists. Detached new construction is most expensive because you are building a complete home from scratch — foundation, framing, roofing, all utilities.
| ADU Type | Typical Size | Cost Range | Key Cost Driver |
|---|---|---|---|
| Garage Conversion | 400–600 sq ft | $60,000 – $110,000 | Insulation, electrical, HVAC, bathroom addition |
| Basement Conversion | 500–800 sq ft | $75,000 – $130,000 | Egress windows, waterproofing, HVAC |
| Attached ADU | 400–800 sq ft | $90,000 – $160,000 | Shared wall framing, separate entrance, utilities |
| Detached ADU (1-story) | 400–800 sq ft | $120,000 – $200,000 | Full foundation, framing, roofing, all utilities |
| Detached ADU (2-story) | 800–1,200 sq ft | $200,000 – $320,000 | Structural engineering, staircase, larger footprint |
| Junior ADU (JADU) | Up to 500 sq ft | $30,000 – $75,000 | Interior conversion only, shared utilities allowed |
3. Full Cost Breakdown: 600 sq ft Detached ADU
The table below reflects actual costs for a standard 600 sq ft detached ADU on a flat lot in LA County in 2026. These are not national averages — they are sourced from real LA County permit records, local supplier pricing, and Skyline Builders project data.
| Cost Category | Low Estimate | High Estimate | Notes |
|---|---|---|---|
| Architectural Plans & Design | $6,000 | $10,000 | Includes structural drawings |
| Permit Fees (LA County) | $5,000 | $8,000 | Varies by jurisdiction |
| Soils Report / Geotechnical | $1,500 | $3,500 | Required on hillside lots |
| Foundation | $12,000 | $22,000 | Slab vs. raised foundation |
| Framing & Structural | $18,000 | $28,000 | Lumber, labor, hardware |
| Roofing | $8,000 | $14,000 | Composition shingle standard |
| Exterior (Stucco/Siding/Windows) | $12,000 | $20,000 | Matching existing home style |
| Electrical (Panel + Wiring) | $8,000 | $14,000 | 200A sub-panel typical |
| Plumbing (Rough + Finish) | $10,000 | $16,000 | Full bath + kitchen |
| HVAC (Mini-Split System) | $5,000 | $9,000 | Per zone, energy efficient |
| Insulation | $3,000 | $5,000 | Title 24 compliance required |
| Drywall & Texture | $5,000 | $8,000 | Includes tape, mud, paint |
| Flooring | $4,000 | $8,000 | LVP standard, tile in wet areas |
| Kitchen (Cabinets + Counters + Appliances) | $8,000 | $18,000 | See Section 6 for detail |
| Bathroom (Tile + Fixtures + Vanity) | $5,000 | $10,000 | See Section 6 for detail |
| Utility Connections (Water/Sewer/Gas) | $8,000 | $18,000 | See Section 7 for detail |
| Landscaping & Site Work | $3,000 | $8,000 | Grading, drainage, walkway |
| Contingency (10%) | $12,150 | $19,950 | Always budget this |
| TOTAL | $133,650 | $219,450 | 600 sq ft detached ADU, flat lot |
4. Plans & Permits: The Real $13,000 Number
One of the most common ways homeowners get surprised is by underestimating the cost of plans and permits. Many contractors quote construction costs only — then the client discovers they owe another $10,000–$15,000 before a single nail is driven.
For a standard 600 sq ft detached ADU in LA County, expect to spend approximately $13,000 on plans and permits. Here is where that money goes:
| Item | Typical Cost | Who Charges It |
|---|---|---|
| Architectural drawings (floor plan, elevations, sections) | $4,000 – $7,000 | Architect or designer |
| Structural engineering calculations & stamp | $1,500 – $3,000 | Licensed structural engineer |
| Title 24 energy compliance report | $500 – $1,000 | Energy consultant |
| LA County building permit | $2,500 – $5,000 | LA County DRP or city |
| School fees (LA Unified) | $1,500 – $3,000 | LAUSD (charged per sq ft) |
| Fire department review | $300 – $600 | LA County Fire |
| Plan check (first submission) | Included in permit fee | Building department |
| Plan check corrections (if required) | $0 – $1,500 | Architect revision time |
Plan check timelines in LA County currently run 8–14 weeks for over-the-counter review and up to 6 months for projects requiring discretionary approval. Skyline Builders submits complete, code-compliant packages on the first attempt, which eliminates costly correction cycles and keeps your project on schedule.
5. Construction Costs: What You're Actually Paying For
Construction costs in Los Angeles are among the highest in the nation. Prevailing wage rates, high insurance costs, and the complexity of building on infill lots all push prices up. Here is what drives the numbers:
| Trade | LA Hourly Rate (2026) | Typical Hours for 600 sq ft ADU | Estimated Labor Cost |
|---|---|---|---|
| Framing carpenter | $75 – $95/hr | 160–200 hrs | $12,000 – $19,000 |
| Electrician (journeyman) | $90 – $115/hr | 80–120 hrs | $7,200 – $13,800 |
| Plumber (journeyman) | $95 – $120/hr | 80–100 hrs | $7,600 – $12,000 |
| HVAC technician | $85 – $110/hr | 40–60 hrs | $3,400 – $6,600 |
| Tile setter | $70 – $90/hr | 40–60 hrs | $2,800 – $5,400 |
| Painter | $55 – $75/hr | 60–80 hrs | $3,300 – $6,000 |
These are licensed, insured, W-2 employee rates — not day labor. Any contractor quoting significantly below these rates is either using unlicensed workers (which voids your homeowner's insurance and exposes you to liability) or they are planning to cut corners on materials.
6. Kitchen & Bathroom: The Detail That Matters
Kitchen and bathroom finishes are where ADU budgets vary most dramatically — and where the biggest gap between a "rental-grade" and "premium" finish lives. Here is a realistic breakdown for both a budget-conscious and a premium finish level:
Kitchen
| Item | Budget (Rental Grade) | Premium |
|---|---|---|
| Prefab cabinets (Home Depot / IKEA) | $2,500 – $3,500 | $6,000 – $12,000 (custom) |
| Quartz countertop (installed) | $1,800 – $2,800 | $4,000 – $7,000 |
| Cabinet assembly & installation labor | $2,500 – $3,000 | $3,500 – $5,000 |
| Appliances (range, dishwasher, fridge) | $1,500 – $2,500 | $4,000 – $8,000 |
| Backsplash tile & installation | $600 – $1,200 | $1,500 – $3,000 |
| Sink & faucet | $300 – $600 | $800 – $2,000 |
| Kitchen subtotal | $9,200 – $13,600 | $19,800 – $37,000 |
Bathroom
| Item | Budget (Rental Grade) | Premium |
|---|---|---|
| Shower tile & installation | $1,200 – $2,000 | $3,000 – $6,000 |
| Vanity (36" with sink) | $400 – $700 | $1,200 – $3,000 |
| Toilet | $200 – $350 | $500 – $1,200 |
| Shower fixtures & hardware | $400 – $800 | $1,500 – $4,000 |
| Floor tile & installation | $600 – $1,000 | $1,500 – $3,000 |
| Mirror & accessories | $150 – $300 | $400 – $1,000 |
| Bathroom subtotal | $2,950 – $5,150 | $8,100 – $18,200 |
7. Utility Connections: The Line Item That Surprises Everyone
Utility connections are consistently the most underestimated cost in ADU budgets. Many homeowners assume their existing service can simply be extended to the ADU — but LA County has specific requirements that often require significant upgrades.
| Utility | Typical Cost | Common Surprise |
|---|---|---|
| Water meter (new service) | $3,000 – $6,000 | LADWP connection fees vary by zone |
| Sewer connection / lateral upgrade | $4,000 – $10,000 | Old clay pipe may require full replacement |
| Electrical service upgrade (2-gang meter) | $4,000 – $8,000 | LA County requires separate meter for ADU |
| Gas service extension | $1,500 – $4,000 | SoCalGas connection + trenching |
| Solar interconnection (if applicable) | $500 – $2,000 | NEM 3.0 may affect sizing |
8. Hidden Costs to Budget For
Beyond the line items above, there are several costs that experienced ADU builders know to budget for — but that rarely appear in a first-pass estimate from a less experienced contractor.
| Hidden Cost | Typical Range | When It Hits |
|---|---|---|
| Temporary power during construction | $800 – $1,500 | Before permanent service is connected |
| Porta-potty rental (4–6 months) | $600 – $1,200 | Required by OSHA on active job sites |
| Dumpster / debris removal | $1,500 – $3,000 | Multiple hauls during construction |
| Soil compaction testing | $500 – $1,000 | Required before foundation pour |
| Special inspection fees | $1,000 – $2,500 | Required for certain structural elements |
| Landscaping restoration | $2,000 – $5,000 | Trenching for utilities damages yard |
| Furnishings (if renting furnished) | $5,000 – $15,000 | Post-construction, optional |
| Property tax reassessment | $1,200 – $3,600/yr ongoing | ADU adds assessed value |
9. Financing & Grants: How to Pay for It
Most homeowners finance their ADU through one of four mechanisms. The right choice depends on your current equity, credit profile, and timeline.
| Financing Option | Typical Amount | Rate (2026) | Best For |
|---|---|---|---|
| Cash-out refinance | $50K – $200K+ | 6.5% – 7.5% | High equity, long-term hold |
| HELOC (Home Equity Line) | $50K – $150K | Prime + 0.5–1% | Phased construction draws |
| Construction-to-perm loan | $100K – $300K | 7% – 8.5% | New builds, converts to mortgage |
| CalHFA ADU Grant | Up to $40,000 | 0% (grant, not loan) | Owner-occupants, income limits apply |
| Personal loan / unsecured | $20K – $50K | 9% – 15% | Garage conversions, smaller projects |
10. ROI: When Does It Pay Off?
At current LA County rental rates, a well-built ADU typically achieves full payback in 7–12 years — and then generates pure passive income for the life of the property. Here is how the math works for a typical Skyline project:
| Scenario | All-In Cost | Monthly Rent | Annual Income | Payback Period |
|---|---|---|---|---|
| Garage conversion (400 sq ft, 1BR/1BA) | $85,000 | $1,600 – $2,000 | $19,200 – $24,000 | 4–5 years |
| Detached ADU (600 sq ft, 1BR/1BA) | $165,000 | $2,200 – $2,800 | $26,400 – $33,600 | 5–7 years |
| Detached ADU (800 sq ft, 2BR/2BA) | $210,000 | $2,800 – $3,500 | $33,600 – $42,000 | 5–7 years |
| Premium detached (1,000 sq ft, 2BR/2BA) | $280,000 | $3,500 – $4,500 | $42,000 – $54,000 | 6–8 years |
11. Red Flags in Contractor Bids
The LA ADU market has attracted a wave of contractors who are either inexperienced with the permitting process or deliberately lowballing to win the job. Here are the red flags that should make you walk away from any bid:
🚩 Bid under $100K for a detached ADU
Impossible at current LA labor and material costs without cutting corners or excluding permits.
🚩 No mention of permit fees in the estimate
Permits and plans are $8,000–$15,000. If they're not in the bid, you'll be surprised later.
🚩 No licensed architect or engineer on the team
LA County requires stamped drawings from a licensed professional. If they're skipping this, they're building without permits.
🚩 Asking for more than 10% upfront
California law limits deposits to 10% or $1,000, whichever is less, for home improvement contracts.
🚩 No mention of the 2-gang meter requirement
Any experienced LA ADU contractor knows about this. If they don't mention it, they haven't done many ADUs in LA County.
🚩 Vague timeline with no milestone schedule
A professional contractor provides a week-by-week schedule. Vague timelines are how projects drag from 6 months to 18 months.
12. Frequently Asked Questions
Can I build an ADU for under $100,000 in LA?
A Junior ADU (JADU) converting existing interior space can be done for $30,000–$75,000. A garage conversion can come in at $60,000–$110,000. But a new detached ADU with a foundation, full utilities, and separate meter will not be done properly for under $120,000 in LA County in 2026.
How long does the whole process take?
Plan to budget 12–18 months from first consultation to move-in. Plans and permits take 2–5 months depending on jurisdiction and project complexity. Construction takes 4–8 months. Skyline Builders' average timeline for a 600 sq ft detached ADU is 14 months from contract to keys.
Do I need to move out during construction?
No. ADU construction on a detached unit does not require you to vacate your main home. There will be noise, dust, and contractor activity on your property, but you can remain in residence throughout the build.
Will my property taxes go up?
Yes, but only on the value of the ADU — not the entire property. Under California's Prop 13 rules, only the new construction is reassessed. A $165,000 ADU might add $1,800–$2,200 per year in property taxes, which is easily offset by rental income.
Can I use the ADU for short-term rentals (Airbnb)?
LA City and most LA County jurisdictions allow short-term rentals only in owner-occupied properties, and only for the primary unit. ADUs are generally not permitted for short-term rental unless you live on-site. Always verify with your local jurisdiction before listing.
What's the best ADU layout for maximum rental income?
A 2-bedroom, 2-bathroom layout in 700–800 sq ft consistently commands the highest rent-per-square-foot in LA County. Placing the second bathroom adjacent to the laundry room saves on plumbing costs and improves livability. A private entrance, covered parking, and in-unit laundry are the three amenities that most increase rental value.
Ready to Get Your Real Number?
Every property is different. The only way to know what your ADU will actually cost is a site visit from an experienced LA County ADU builder. Skyline Builders provides a detailed, line-item estimate within 48 hours of your free consultation — no obligation, no pressure.