ADU Cost Guide · California
Prefab ADU Cost California — Starting at $79K All-In
Full cost breakdown for California prefab ADUs — what drives the price, what's included in our all-in quote, and how factory-built saves you 30–50% over site-built.
Prefab ADU vs Site-Built — What It Actually Costs in California
Real numbers. No ranges so wide they're useless.
Site-Built ADU in California
Epic Modulars Prefab ADU
Why Factory-Built ADUs Cost Less — Not Because They're Cheaper
Same materials. Same codes. Different economics.
Bulk Purchasing
Factories buy lumber, fixtures, flooring, and appliances at volume contractor-plus pricing. A general contractor buying materials for one custom ADU pays retail or single-job contractor rates — we pay significantly less per unit.
No Subcontractor Stack
Site-built ADUs pass through a general contractor who marks up every subcontractor — framing, electrical, plumbing, tile, paint. Our factory employs all trades in-house, eliminating 15–25% markup at each layer.
Zero Weather Delay
A site-built ADU loses days — sometimes weeks — to rain, wind, and heat. Factory builds run on a fixed schedule regardless of weather. Those delays cost real money in contractor overhead, equipment rental, and extended timelines.
Every Dollar in Your All-In Price Covers
This is what “all-in” actually means at Epic Modulars.
Prefab ADU Cost FAQs
What is the total cost breakdown for a prefab ADU in California?
An Epic Modulars prefab ADU all-in price covers: permits and plan check fees ($5,000–$15,000 depending on city), factory construction ($55,000–$90,000 depending on size), delivery and crane set ($3,000–$6,000), foundation and site preparation ($8,000–$15,000), utility connections — water, sewer, electric ($5,000–$12,000), and final inspections. Everything is bundled into one contract price starting at $79,000. No line items hit you separately.
What is included in an all-in prefab ADU price?
At Epic Modulars, all-in means: full permit management from submittal to sign-off, HCD-certified factory construction, LVP flooring, quartz countertops, stainless steel appliances, delivery to your California property, foundation and site prep, all utility connections, final city inspection coordination, HOA coordination where required, 1-year workmanship warranty, and manufacturer warranties on all major components. Nothing is excluded and then billed back at the end.
How is a prefab ADU cheaper than a site-built ADU?
Factory construction cuts costs in three ways: bulk material purchasing (factories buy at contractor-plus volume), consistent labor (the same crews repeat the same builds efficiently, with no subcontractor markups), and weather-independent scheduling (no rain delays, no idle days). Site-built ADUs in California typically run $180–$450 per square foot before permitting and site work. Factory-built units run significantly less because the overhead structure is different. You're not paying for a contractor's project management markup on top of every subcontractor.
Are there financing options for a prefab ADU in California?
Yes. Most Epic Modulars buyers use one of three paths: a home equity line of credit (HELOC) or cash-out refinance on their existing home equity, a construction-to-permanent loan specifically for ADUs, or California's ADU financing programs through the CalHFA ADU Grant Program (up to $40,000 for qualifying homeowners) and local ADU loan programs in cities like San Jose, Oakland, and LA. We can connect you with lenders experienced in ADU financing — ask during your quote call.
Are there hidden costs in a prefab ADU project?
With Epic Modulars, no — we build everything into the contract price before you sign. However, there are costs outside any builder's control: property tax reassessment (your assessed value increases by the ADU's value — typically $500–$1,500/year additional), impact fees in some cities (we include standard permit fees; if your city charges extraordinary impact fees we'll flag them upfront), and utility connection upgrades if your existing service panel needs expansion. We identify site-specific issues during our initial site assessment so you know the full picture before committing.
Get an Exact Price for Your Property
Every lot is different. Tell us your address and we'll give you a real number — not a range so wide it means nothing.
Get My All-In ADU Price