If you are planning to add an accessory dwelling unit to your California property, the first big question is usually about money. Should you go with a prefab ADU vs stick built with traditional on-site construction? Both options come with real trade-offs, and the sticker price you see online rarely tells the full story.
At Nestadu, we walk California homeowners through this decision every week. Here is an honest look at what each option actually costs, what gets left out of most quotes, and how to figure out which path makes sense for your property and your goals.
What Is a Prefab ADU?
A prefab (or modular) ADU is built off-site in a factory setting. Once the unit is finished, it gets delivered to your property on a truck and placed onto a prepared foundation. Some prefab companies build the entire unit as one piece, while others ship it in panels that get assembled on-site.
Prefab ADUs appeal to homeowners who want a faster timeline and fewer surprises with pricing. The factory environment means weather delays are not a factor during construction, and quality control tends to be consistent since the same crews build units on a repeating schedule.
What Is a Stick-Built ADU?
A stick-built ADU is constructed the traditional way, right on your property from the ground up. Framing, roofing, plumbing, electrical, and finishes all happen on-site, just like building a small home.
This method gives you complete control over the design. You can match the architecture of your existing house, adjust room layouts to fit an unusual lot, or add custom features like vaulted ceilings or specialty finishes. If your property has access challenges or you want something truly one-of-a-kind, stick-built is often the better fit.
Breaking Down the Real Costs: Prefab ADU
The base price for a prefab ADU in California typically falls between $150 and $300 per square foot, depending on the size, model, and level of finishes you choose. For a standard 500 to 800 square foot unit, that puts the starting range somewhere around $100,000 to $240,000 for the unit itself.
But the unit price is not the whole picture. Here is what often gets left out of prefab quotes:
- Foundation and site preparation can add $15,000 to $40,000 depending on your lot’s grading and soil conditions
- Utility hookups for water, sewer, and electrical typically run $10,000 to $30,000 or more
- Permits and city fees in many California cities range from $5,000 to $20,000+
- Crane and delivery fees vary based on access to your backyard, sometimes costing $5,000 to $15,000
- Finish upgrades beyond the base package can quickly add another $10,000 to $25,000
When you add everything up, a typical all-in cost for a prefab ADU in California lands somewhere between $180,000 and $350,000 for most projects. That is a significant jump from the base price many homeowners see when they first start shopping.
Breaking Down the Real Costs: Stick-Built ADU
Stick-built ADUs in California generally cost between $250 and $500 per square foot, depending on the region, complexity of design, and material choices. For a comparable 500 to 800 square foot unit, you are looking at $150,000 to $400,000 or more for the full build.
The additional expenses to plan for are similar but tend to be more visible in the bidding process:
- Architecture and design fees usually run $5,000 to $15,000
- Permits and impact fees follow the same California fee structures
- Site work, grading, and foundation costs overlap with prefab but can be more flexible since the builder adapts the design to your lot
- Utility connections and potential panel upgrades are comparable to prefab costs
- Landscaping restoration after months of on-site work can add $3,000 to $10,000
The realistic all-in range for a stick-built ADU in California sits between $200,000 and $450,000, depending on your choices and location. The higher end reflects fully custom designs with premium finishes.
Side-by-Side Comparison: Prefab ADU Cost vs Stick Built
When you compare the two approaches for a typical 600 to 800 square foot ADU in California, the gap is smaller than most people expect once you factor in all the extras. Here is how the numbers stack up across every major category.
| Category | Prefab ADU | Stick-Built ADU |
| Cost Per Square Foot | $150 – $300 | $250 – $500 |
| All-In Total Cost | $180,000 – $350,000 | $200,000 – $450,000 |
| Foundation & Site Prep | $15,000 – $40,000 | $15,000 – $45,000 |
| Permits & City Fees | $5,000 – $20,000+ | $5,000 – $20,000+ |
| Utility Hookups | $10,000 – $30,000 | $10,000 – $30,000 |
| Typical Timeline | 3 – 5 months | 6 – 12 months |
| Design Customization | Limited to available plans | Fully custom |
| Neighborhood Integration | Moderate | Seamless |
| Long-Term Appraisal Value | Good | Higher |
| Backyard Disruption | Minimal | Significant |
Prefab tends to save 10% to 20% on total cost for straightforward projects. But that savings shrinks fast once you start adding upgrades, dealing with a tricky lot, or running into delivery access problems.
Which Option Gives You Better Long-Term Value?
Cost is just one part of the equation. If you are building an ADU as a long-term investment, the value it adds to your property matters just as much as what you spend today.
Stick-built ADUs generally appraise higher because they are fully custom and blend seamlessly with the main home. Buyers and appraisers tend to view them the same way they view any well-built addition. For homeowners planning to sell or refinance down the road, this can make a meaningful difference.
Prefab ADUs, on the other hand, get you to rental income faster. If your primary goal is cash flow from a rental unit or providing housing for a family member quickly, the shorter timeline can be worth the trade-off in long-term appraisal value.
How Nestadu Helps You Make the Right Call
At Nestadu, we believe the right choice depends entirely on your property, your budget, and what you want the space to do for your life. Our team specializes in building high-quality ADUs across California, and we are upfront about pricing from the very first conversation. No hidden fees, no surprise line items.
Whether you are leaning toward a prefab approach or a fully custom stick-built design, we can walk you through the numbers for your specific lot and help you make a decision you feel confident about. Reach out to Nestadu for a personalized consultation and get a clear picture of what your ADU project will actually cost.