Adding square footage to your California home is a significant investment. Here's what you can expect to pay for various types of additions.
Average Home Addition Costs
| Addition Type | Cost per Sq Ft | Total Range |
|---|---|---|
| Basic Room Addition | $250-$400 | $50,000-$100,000 |
| Bedroom + Bathroom | $350-$500 | $70,000-$150,000 |
| Second Story | $300-$500 | $150,000-$500,000 |
| ADU (Detached) | $350-$600 | $150,000-$350,000 |
What Drives Costs?
Foundation Work
- Slab-on-grade: $5-$12 per sq ft
- Raised foundation: $10-$20 per sq ft
- Second story (structural reinforcement): Varies widely
Roofing Integration
Tying into existing rooflines adds complexity and cost. Budget $10,000-$30,000 for roof work.
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California's ADU laws make building easier, but costs remain significant:
- Garage conversion: $100,000-$180,000
- Attached ADU: $150,000-$250,000
- Detached ADU: $180,000-$350,000
- Prefab ADU: $120,000-$200,000
Timeline Expectations
- Planning and permits: 2-4 months
- Construction (small addition): 3-4 months
- Construction (large addition): 4-8 months
- Second story: 6-12 months
Permit and Soft Costs
Don't forget non-construction expenses:
- Architecture/design: 5-15% of construction cost
- Engineering: $2,000-$10,000
- Permits: $3,000-$20,000
- Utility connections: $2,000-$10,000
Regional Variations
California costs vary by location:
- Bay Area: $400-$700 per sq ft
- Los Angeles: $350-$550 per sq ft
- San Diego: $300-$500 per sq ft
- Central California: $250-$400 per sq ft
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