Garage Conversion vs. New Construction ADU: Which Is Right for You?
Jaime Costilla ·
The Big Decision: Convert or Build New?
This is the #1 question we hear from homeowners. Both options are excellent — but which one is right for YOUR situation? Let's break it down.
Cost Comparison
| Factor | Garage Conversion | New Construction ADU |
|---|---|---|
| Total cost | $100,000-$200,000 | $200,000-$400,000 |
| Cost per sq ft | $200-$350 | $300-$500 |
| Typical size | 400-600 sq ft | 600-1,200 sq ft |
| Foundation work | Minimal (existing slab) | Full new foundation |
| Timeline | 3-5 months | 6-12 months |
Timeline Comparison
Garage Conversion: 3-5 Months
- Design & permits: 4-8 weeks
- Construction: 8-12 weeks
- Final inspections: 1-2 weeks
New Construction ADU: 6-12 Months
- Design & engineering: 6-10 weeks
- Permits: 6-12 weeks
- Site work & foundation: 3-4 weeks
- Framing through finish: 12-20 weeks
- Final inspections: 2-3 weeks
Rental Income Comparison
Garage conversions typically generate 85-90% of the rental income of a new construction ADU, at 40-50% of the cost. Here's why:
- A well-designed 500 sq ft garage conversion in Pasadena rents for $2,200-$2,600/month
- A 900 sq ft new construction ADU in Pasadena rents for $2,800-$3,400/month
- The garage conversion costs $150K but earns $2,400/month = 19.2% annual return
- The new construction costs $300K but earns $3,100/month = 12.4% annual return
When to Choose Garage Conversion
- You want to start generating income fast
- Your budget is under $200,000
- You have an existing two-car garage
- You don't need the garage for parking
- ROI is your primary goal
When to Choose New Construction
- You want a larger unit (750+ sq ft)
- You want to maximize property value increase
- You need to keep your garage
- You have a large backyard with room
- You're building for family (not primarily rental)
- You want to potentially sell it separately under AB 1033
The Best of Both Worlds
Some homeowners do BOTH — convert the garage now for immediate income, then build a new construction ADU later. California law allows an ADU + JADU on single-family lots, and some cities allow even more flexibility.
Our Recommendation
For most homeowners, we recommend starting with a garage conversion. The faster timeline, lower cost, and higher ROI make it the smarter first move. Use the rental income to fund a future new construction ADU if you want to expand later.
Not sure which option fits your property? Book a free site assessment and we'll evaluate both options for your specific lot.