ADU Construction Guide
Everything you need to know about building your ADU in California
Getting Started with ADU Construction
Pre-Construction Checklist
Documentation
- Approved building permits
- Construction drawings
- Engineering calculations
- Site survey
- Utility plans
Site Preparation
- Property line verification
- Utility locating
- Soil testing
- Tree protection
- Access planning
Team Assembly
- General contractor selection
- Subcontractor coordination
- Material suppliers
- Inspection scheduling
- Project management plan
Construction Methods
Traditional Site-Built
Advantages
- Maximum customization
- Adaptable to site conditions
- Local contractor availability
- Phased construction possible
Timeline
4-8 months typical
Cost Range
$300-400/sq ft
Modular/Prefabricated
Advantages
- Faster construction
- Quality control
- Weather-independent building
- Predictable costs
Timeline
2-4 months typical
Cost Range
$250-350/sq ft
Panelized Systems
Advantages
- Reduced on-site time
- High energy efficiency
- Structural integrity
- Design flexibility
Timeline
3-6 months typical
Cost Range
$275-375/sq ft
Materials & Systems
Structural Systems
Foundation Systems
Finding Qualified Contractors
Contractor Requirements
In California, ADU contractors must meet specific requirements:
- Valid California Contractor's License (B-General Building)
- Workers' compensation insurance
- Liability insurance
- Local business licenses
- Bonding requirements
Selection Process
1
Research
- Check CSLB license status
- Read online reviews
- View completed projects
- Verify insurance
2
Interview
- ADU experience
- Local code knowledge
- Project timeline
- Communication style
3
Verify
- Contact references
- Visit past projects
- Check complaints
- Review licenses
4
Compare
- Detailed bids
- Scope of work
- Timeline commitments
- Payment terms
Red Flags to Watch For
Pricing Issues
- Unusually low bids
- Large upfront payments
- Cash-only deals
- Pressure tactics
Documentation
- No written contract
- Missing licenses
- No insurance proof
- Vague proposals
Communication
- Poor responsiveness
- Unclear timeline
- No references
- Evasive answers
Construction Timeline
Phase 1: Site Preparation
1-2 Weeks
- Site clearing
- Utility locating
- Grading
- Erosion control
Phase 2: Foundation
2-3 Weeks
- Excavation
- Forming
- Reinforcement
- Concrete placement
Phase 3: Framing
3-4 Weeks
- Wall framing
- Roof framing
- Sheathing
- Weather barrier
Phase 4: Systems
3-4 Weeks
- Electrical
- Plumbing
- HVAC
- Insulation
Phase 5: Finishes
4-6 Weeks
- Drywall
- Flooring
- Cabinets
- Fixtures
Phase 6: Completion
1-2 Weeks
- Final inspections
- Punch list
- Cleaning
- Certificate of occupancy
Inspections & Compliance
Required Inspections
Foundation
- Soil compaction
- Forms and reinforcement
- Drainage systems
- Waterproofing
Framing
- Wall construction
- Roof structure
- Shear walls
- Hardware installation
Mechanical
- Electrical rough-in
- Plumbing rough-in
- HVAC installation
- Gas lines
Final
- Life safety systems
- Energy compliance
- Accessibility
- Site work completion
Ready to Start Your ADU Project?
Let us help you find qualified contractors and guide you through the construction process.