How Long Does It Take to Build an ADU in Los Angeles?

One of the most common questions homeowners ask when planning an ADU is: “How long will this take?” The complete timeline from initial planning to move-in ready typically ranges from 6-18 months in Los Angeles, depending on project complexity, permit processing times, and construction type. This comprehensive guide breaks down every phase of ADU construction so you know exactly what to expect.

Quick Timeline Overview

ADU Type	Fastest Possible	Typical Timeline	Complex Projects
Pre-Approved Plans (New Construction)	5-7 months	7-10 months	10-14 months
Custom Design (New Construction)	8-10 months	10-14 months	14-18 months
Garage Conversion	4-6 months	6-9 months	9-12 months
Attached ADU	5-7 months	7-11 months	11-15 months
JADU (Interior Conversion)	3-5 months	5-7 months	7-10 months
Prefab/Modular ADU	4-6 months	6-9 months	9-12 months

Complete Phase-by-Phase Timeline

Phase 1: Initial Planning & Decision Making

Duration: 2-6 weeks

Task	Time Required	Details
Research & education	1-2 weeks	Learning about ADUs, regulations, options
Budget development	3-5 days	Determining financing, getting estimates
Property assessment	1-2 weeks	Understanding your lot’s potential, constraints
Contractor selection	1-3 weeks	Interviewing, comparing bids, checking references
Contract negotiation	3-7 days	Finalizing scope, pricing, timeline

Pro Tip:Use our ADU Eligibility Check and Cost Calculator to accelerate this phase.

Phase 2: Design & Engineering

Duration: 4-12 weeks

Option A: Pre-Approved Standard Plans

Duration: 4-6 weeks

Select from LA’s Standard Plan Program
Plans already reviewed and approved by LADBS
Minimal customization (mainly site-specific details)
Architectural review: 1-2 weeks
Site-specific engineering: 2-3 weeks
Survey and civil work: 1-2 weeks

Typical cost: $5,000 – $12,000

Option B: Custom Design

Duration: 8-12 weeks

Design Stage	Duration	Deliverables
Initial Consultation	1 week	Program requirements, preliminary concepts
Schematic Design	2-3 weeks	Floor plans, elevations, design direction
Design Development	2-3 weeks	Refined plans, materials selection, 3D renders
Construction Documents	3-4 weeks	Detailed plans for permitting and construction
Structural Engineering	2-3 weeks	Foundation, framing calculations (concurrent)
MEP Engineering	2-3 weeks	Mechanical, electrical, plumbing (concurrent)
Civil/Survey	1-2 weeks	Site plan, grading, utility locations

Typical cost: $12,000 – $30,000

Time-Saving Strategy: Many of these tasks can run concurrently with experienced design teams.

Phase 3: Permit Application & Approval

Duration: 6-16 weeks

Ministerial ADU Approval (Most ADUs)

Target: 60 days per state law, Reality: 8-16 weeks

Step	Timeline	Notes
Plan check submission	1-3 days	Online submission via LADBS
Initial review	2-4 weeks	LADBS first review cycle
Corrections/resubmittal	1-2 weeks	Address review comments
Second review	2-3 weeks	Verify corrections
Additional reviews (if needed)	2-4 weeks	Complex projects may need 3rd review
Permit issuance	3-5 days	After final approval

Common Delays:

Incomplete plan sets: +2-4 weeks
Hillside/coastal zone properties: +4-8 weeks additional review
HPOZ (Historic) districts: +3-6 weeks for design review
Easement issues: +2-6 weeks to resolve
Unpermitted work discovered: +4-12 weeks to remediate

Note:If you have existing code violations or unpermitted construction, these must be resolved before ADU permits are issued. As code compliance specialists, we can help expedite this process.

Discretionary Review Projects

Duration: 4-9 months (rare for standard ADUs)

Required if your ADU needs:

Variance
Conditional Use Permit
Environmental review
Coastal Commission approval

Most standard ADUs avoid discretionary review thanks to state law.

Phase 4: Pre-Construction

Duration: 2-4 weeks

Task	Duration	Details
Finalize material selections	1 week	Finishes, fixtures, appliances, colors
Order long-lead items	Ongoing	Windows, doors, special materials
Schedule subcontractors	1 week	Coordinate trades, timelines
Site preparation planning	3-5 days	Access, staging, protection of existing
Underground utility location	1-2 weeks	Call 811, private locates if needed
Tree protection (if required)	1-3 days	Fencing, protective measures

Phase 5: Construction

Duration: 16-32 weeks

Detailed Construction Timeline (800 sq ft Detached ADU Example)

Construction Phase	Duration	Key Activities
Week 1-2: Site Preparation	1-2 weeks	– Establish access routes – Set up temporary fencing – Demolition if needed – Clear and grade site – Tree protection
Week 2-3: Rough Grading & Utilities	1-2 weeks	– Excavation for utilities – Trenching for water, sewer, electric – Underground conduit installation – Rough grading – Compaction testing
Week 3-6: Foundation	3-4 weeks	– Foundation excavation – Rebar installation – Plumbing under-slab – Foundation inspection – Concrete pour – Cure time (7+ days) – Backfill and compact
Week 7-12: Framing	5-6 weeks	– Floor framing (if raised) – Wall framing – Roof framing – Sheathing – Framing inspection – Windows and exterior doors – House wrap/weather barrier
Week 13-14: Roofing	1-2 weeks	– Underlayment – Roofing material installation – Flashing – Gutters – Roof inspection
Week 13-17: Rough Mechanicals	4-5 weeks	– Rough plumbing – Rough electrical – HVAC installation – Ductwork – Gas lines (if applicable) – Rough inspection (critical milestone)
Week 17-19: Insulation & Drywall	2-3 weeks	– Insulation installation – Insulation inspection – Drywall hanging – Taping and mudding – Sanding – Texture
Week 19-21: Exterior Finishes	2-3 weeks	– Siding installation – Exterior paint/stain – Trim work – Soffit and fascia – Exterior lighting
Week 21-26: Interior Finishes	5-6 weeks	– Interior paint – Flooring installation – Cabinets – Countertops – Trim and doors – Tile work (bathroom/kitchen) – Hardware installation
Week 26-28: Finish Mechanicals	2-3 weeks	– Plumbing fixtures – Electrical fixtures – HVAC registers/thermostats – Appliance installation – Final connections
Week 28-30: Final Details	2-3 weeks	– Touch-up painting – Hardware adjustments – Landscaping restoration – Driveway/walkways – Final cleaning – Punch list items
Week 30-32: Inspections & Close-out	2-3 weeks	– Final building inspection – Final electrical inspection – Final plumbing inspection – Final mechanical inspection – Corrections if needed – Certificate of Occupancy

Total Construction: 20-32 weeks (5-8 months)

Construction Timeline Variations by ADU Type

Garage Conversion (600 sq ft):

Site prep: 1 week (minimal)
Foundation: Already exists (repairs only: 1-2 weeks)
Framing: 2-3 weeks (interior partitions, openings)
Utilities: 2-3 weeks (shorter runs)
Finishes: 4-6 weeks
Total: 12-20 weeks

Attached ADU (700 sq ft):

Site prep: 1 week
Foundation: 2-3 weeks (ties into existing)
Framing: 4-5 weeks (one wall exists)
Roof integration: 1-2 weeks
Utilities: 3-4 weeks
Finishes: 5-7 weeks
Total: 16-24 weeks

Two-Story ADU (1,200 sq ft):

Site prep: 2 weeks
Foundation: 4 weeks (larger, more complex)
Framing: 8-10 weeks (two stories)
Utilities: 5-6 weeks (two floors)
Finishes: 8-10 weeks (twice the area)
Total: 28-40 weeks

Common Delays and How to Avoid Them

Top 10 Timeline Killers

Delay Cause	Typical Impact	Prevention Strategy
Permit plan corrections	+4-8 weeks	Hire experienced designers; submit complete, accurate plans
Unpermitted existing work	+6-16 weeks	Identify and resolve before ADU application
Material delivery delays	+2-6 weeks	Order long-lead items early; have backup options
Weather delays	+1-4 weeks	Plan around rainy season; have weather contingencies
Failed inspections	+1-3 weeks each	Work with experienced contractors; pre-inspect internally
Subcontractor scheduling	+2-6 weeks	Lock in subs early; have backup trades lined up
Design changes mid-project	+2-8 weeks	Finalize all decisions before breaking ground
Utility connection delays	+3-8 weeks	Apply for utility services early; coordinate with DWP
Easement/title issues	+4-12 weeks	Order title report during design phase
Soil/foundation issues	+2-6 weeks	Geotechnical survey for hillside/problem soils

Seasonal Considerations

Season	Pros	Cons	Timeline Impact
Spring (Mar-May)	Good weather, full work days	Contractor availability tight	Standard timeline
Summer (Jun-Aug)	Long days, minimal rain	Very hot, vacation schedules	Standard timeline
Fall (Sep-Nov)	Ideal weather, good availability	Holiday slowdowns late	Standard to +1 week
Winter (Dec-Feb)	Better contractor availability	Rain delays, holidays, short days	+2-4 weeks typical

Best time to start permitting: Fall (Oct-Nov) to get permits by spring

Best time to start construction: Late spring (Apr-May) to finish before winter

Timeline Acceleration Strategies

How to Shorten Your ADU Timeline

Use Pre-Approved Plans
- Saves 4-6 weeks in design
- Faster permit approval (as low as 30-60 days)
- Plans already vetted for code compliance
- Total time savings: 6-10 weeks
Hire Design-Build Contractor
- Single point of contact
- Concurrent design and permitting prep
- Better coordination = fewer delays
- Total time savings: 3-6 weeks
Resolve Existing Violations Early
- Don’t wait for plan check to discover issues
- Proactively legalize unpermitted work
- We specialize in code compliance and violation remediation
- Total time savings: 6-12 weeks
Pre-Order Long-Lead Materials
- Windows: 6-12 week lead time
- Custom doors: 8-14 weeks
- Appliances: 4-8 weeks
- Order during permitting phase
- Total time savings: 4-8 weeks
Consider Prefab/Modular
- Manufactured while permits process
- Faster on-site installation (2-4 weeks vs 20-30)
- Weather-independent factory construction
- Total time savings: 8-16 weeks
Fast-Track Financing
- Get pre-approved before design
- Have funding ready when permits issued
- Avoid construction delays waiting for loan
- Total time savings: 2-6 weeks
Make All Decisions Early
- Finalize finishes before permits submitted
- No mid-construction changes
- Keeps project on schedule
- Total time savings: 2-4 weeks
Work with Experienced ADU Specialist
- Knows LADBS processes and inspectors
- Anticipates and prevents issues
- Established trade relationships
- Total time savings: 4-8 weeks

Combined potential time savings: 3-6 months off total timeline

Realistic Timeline Expectations by Project Complexity

Simple/Fast-Track Project

Total: 5-8 months

Characteristics:

Pre-approved plans or simple custom design
Flat lot, no easements or unusual constraints
No existing violations
Standard finishes, readily available materials
Garage conversion or small detached ADU
Experienced contractor
No weather delays

Timeline breakdown:

Planning: 2-3 weeks
Design: 4-6 weeks
Permits: 8-12 weeks
Pre-construction: 2 weeks
Construction: 12-20 weeks

Typical/Average Project

Total: 10-14 months

Characteristics:

Custom design, moderate complexity
Standard residential lot
Some site challenges (slope, access, utilities)
Mid-range finishes
Detached or attached ADU, 600-900 sq ft
Normal permitting timeline
Some minor delays expected

Timeline breakdown:

Planning: 3-6 weeks
Design: 8-12 weeks
Permits: 12-16 weeks
Pre-construction: 3 weeks
Construction: 20-28 weeks

Complex/Extended Project

Total: 14-20 months

Characteristics:

Complex custom design
Hillside, coastal zone, or HPOZ property
Easement issues or lot constraints
Existing violations requiring remediation
High-end finishes, custom materials
Two-story or large ADU (1,000-1,200 sq ft)
Additional agency approvals needed
Winter construction period

Timeline breakdown:

Planning: 6-8 weeks
Design: 12-16 weeks
Permits: 16-24 weeks
Pre-construction: 4 weeks
Construction: 28-40 weeks

Month-by-Month: What to Expect

Typical 12-Month ADU Project Calendar

Month	Phase	What’s Happening	Your Involvement
Month 1	Planning	Research, contractor selection, initial meetings	HIGH – Many decisions to make
Month 2	Design Start	Schematic design, preliminary drawings	HIGH – Design input and approvals
Month 3	Design Completion	Final plans, engineering, material selections	MEDIUM – Finalize finishes and details
Month 4	Permit Submission	Plans submitted to LADBS, initial review	LOW – Waiting for city review
Month 5	Permit Review	Plan check corrections, resubmittals	LOW – Contractor handles corrections
Month 6	Permit Approval	Final permit issued, pre-construction prep	MEDIUM – Final material orders, scheduling
Month 7	Early Construction	Site prep, utilities, foundation	LOW – Progress monitoring
Month 8	Framing	Structure goes up, big visual progress	LOW – Weekly check-ins
Month 9	Rough Mechanicals	Plumbing, electrical, HVAC, roofing	LOW – Occasional site visits
Month 10	Drywall & Exteriors	Insulation, drywall, siding, windows	MEDIUM – Color/finish confirmations
Month 11	Finishes	Paint, flooring, cabinets, fixtures	MEDIUM – Walkthrough, punch list
Month 12	Final & Closeout	Final touches, inspections, Certificate of Occupancy	HIGH – Final inspection, move-in prep

Inspection Timeline & Requirements

Required Inspections During Construction

Inspection Type	When Required	Typical Wait Time	Common Issues
Foundation	Before concrete pour	1-3 days	Rebar spacing, embedments
Under-Slab Plumbing	Before foundation pour	1-2 days	Pressure test, proper slope
Framing	After framing complete	1-3 days	Structural connections, blocking
Rough Plumbing	After rough-in, before insulation	1-3 days	Proper venting, water test
Rough Electrical	After rough-in, before insulation	1-3 days	Box fill, wire sizing, grounding
Rough Mechanical	After HVAC install, before insulation	1-3 days	Duct sizing, proper installation
Insulation	After insulation, before drywall	1-2 days	R-value, coverage, air sealing
Final Building	After completion	3-7 days	Code compliance, safety features
Final Plumbing	After fixtures installed	1-3 days	Fixture installation, water test
Final Electrical	After all electric complete	1-3 days	GFCI/AFCI, panel labeling
Final Mechanical	After HVAC complete	1-3 days	Proper operation, Title 24

Total inspection time built into schedule: 2-4 weeks

After Construction: Move-In Timeline

Duration: 1-3 weeks after final inspection

Final cleaning: 1-2 days
Utility activation: 3-5 days
Landscaping completion: 1-2 weeks
Furnishing (if applicable): 1-2 weeks
For rentals: Marketing and tenant screening: 2-6 weeks

Project Management: Staying On Schedule

Critical Success Factors

Experienced Contractor– Single biggest factor in on-time completion
Clear Communication– Weekly updates, immediate issue resolution
Buffer Timeline– Add 15-20% contingency to estimates
Decision Readiness– Make choices quickly when needed
Inspection Coordination– Don’t let inspections create delays
Weather Planning– Have rain delay contingencies
Material Management– Order early, have backups ready
Trade Coordination– Keep subcontractors on schedule

Get Started with Realistic Timelines

Understanding the ADU timeline helps you plan accordingly – whether you’re timing a rental income start, coordinating with family moves, or budgeting for temporary housing during construction.

As experienced Los Angeles ADU contractors, we help you navigate every phase:

Accurate timeline projections for your specific project
Streamlined permitting and code compliance
Resolution of existing violations before starting
Proactive project management to prevent delays
From initial concept to Certificate of Occupancy

Start your ADU journey with our ADU Eligibility Check and Cost Calculator to understand your project timeline and budget.

Bottom line: Plan for 10-14 months for a typical ADU project, hope for 8-10 months with good luck and planning, and be prepared for 14-18 months if complications arise.

ADU Eligibility Check

ADU Cost Calculator