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Call (916) 436-3776Build an ADU San Bernardino County
How Do I Build an ADU in San Bernardino County and Pay for It?
Building an ADU in San Bernardino County typically costs $150 to $400 per square foot, most projects run $180,000 to $360,000, financed with home equity, a renovation loan, or a construction loan. California's 2026 rules help: a CalHFA grant of up to $40,000 covers predevelopment costs, SB 937 lets you defer most impact fees until final inspection, and units under 750 sq ft skip most impact and school fees. With rents of $1,200 to $2,300 a month, a well-planned ADU often returns 8 to 12% a year. Ashlar Lending arranges the financing; Serve First values the result.
San Bernardino County ADU-build snapshot (2026)
$180K to $360K
Typical ADU build cost
Up to $40,000
CalHFA grant for predevelopment costs
$1,200 to $2,300/mo
Typical ADU rent in this market
~8 to 12%/yr
Typical return on a well-planned ADU
Figures reflect 2026 rules and typical costs and change over time. Serve First Realty is a licensed California real estate brokerage, not a lender or contractor. Loan terms are set by the lender; construction is performed by your licensed contractor.
How to fund and build an ADU in San Bernardino County
An ADU is mostly a money-and-permits project, the construction is the easy part once those are handled. Here's the path, with Ashlar Lending on the financing and Serve First on the value:
Know what it costs
Most ADUs run $150 to $400 per square foot, putting a typical build in the $180,000 to $360,000 range depending on size, finishes, and whether it's a garage conversion (cheaper) or new detached construction. Get a real contractor bid before financing so the loan matches the true cost.
Choose how to pay for it
The main routes are a cash-out refinance or HELOC (tapping existing home equity), a renovation loan (based on your home's after-improvement value), or a construction loan (funds released in draws as work completes). Ashlar Lending can walk you through which fits your equity, budget, and timeline, and model the payment against expected rent.
Tap the CalHFA grant and fee breaks
California's CalHFA ADU program offers up to $40,000 toward predevelopment costs, plans, permits, soil tests, impact fees, with priority for lower-income applicants; it was renewed with expanded funding for 2026. Separately, SB 937 lets you defer most impact fees until final inspection (easing cash flow during the build), and units under 750 sq ft are exempt from most impact and school fees. Ashlar Lending can point you to these programs.
Move fast on permits
Your local agency must act on a complete ADU application within 60 days or it's deemed approved, and pre-approved plan sets (required statewide by 2026 under AB 434) can cut design time and cost. No owner-occupancy is required for a standard ADU, so you can plan to rent it from day one in San Bernardino County.
Make the rent cover the payment
The whole game is cash flow: if the ADU rents for $1,200 to $2,300 a month in San Bernardino County and the financing payment is below that, the unit pays for itself and then some. Ashlar Lending models this rent-vs-payment math up front so you build with confidence, and Serve First confirms the value the ADU adds to your property.
Get a real bid and a real rent estimate before you finance. ADU budgets slip when the loan is sized off a rough guess. Have a licensed contractor bid the actual scope, and have Serve First estimate realistic rent and added value for your specific San Bernardino County location, so Ashlar Lending can size financing to numbers that hold up, not optimistic ones.
One family. Financing, property, and paperwork.
Fund the build, and make the numbers work
Building an ADU is largely a financing project. The Ashlar Brands family helps you pay for it and put it to work:
- Ashlar Lending Inc. (NMLS #2699657) can arrange construction or renovation financing to build your ADU, tapping home equity, a renovation loan, or a construction loan, and can model the rent-vs-payment math so the project pencils. We can also point you to programs like the state’s CalHFA ADU grant.
- Serve First Realty can tell you how much an ADU will add to your property’s value and rentability, useful before you spend, and essential if you may sell later.
- Ashlar LDA, Inc., a bonded and registered Legal Document Assistant, can prepare related deeds and documents at your direction.
These are separate businesses in the Ashlar Brands family. Serve First is a real estate brokerage, not a lender or contractor; loan terms are set by the lender and construction is performed by your licensed contractor. A Legal Document Assistant prepares documents at your direction and is not a substitute for an attorney.
Building an ADU in San Bernardino County: the steps
Get a contractor bid and rent estimate
Start with a real construction bid and a Serve First rent-and-value estimate for your San Bernardino County property, so every number that follows is grounded.
Structure the financing
Ashlar Lending matches you to the right tool, equity, renovation loan, or construction loan, and models the payment against expected rent, factoring in the CalHFA grant and deferred fees.
Permit and build
Use pre-approved plans where possible, submit for the 60-day approval, and build. SB 937 lets you defer most impact fees to final inspection, easing cash flow.
Rent it and enjoy the return
Once it's finaled, the ADU can start generating $1,200 to $2,300 a month, covering the payment and adding lasting value to your home.
Free calculator
ADU Cost & ROI Calculator
Estimate build cost, rental income, and payback for an ADU.
Estimate cost & returnFrequently asked questions
How much does it cost to build an ADU?
Most ADUs cost $150 to $400 per square foot, so a typical build lands between $180,000 and $360,000. Garage conversions sit at the lower end; new detached units with high-end finishes run higher. Always base your financing on an actual contractor bid rather than a rule of thumb, since site conditions and finishes move the number a lot in San Bernardino County.
How do I finance an ADU if I don't have cash?
Three common routes: tap existing home equity (cash-out refinance or HELOC), use a renovation loan based on your home's after-improvement value, or use a construction loan that releases funds in draws as work is completed. Ashlar Lending can explain which fits your situation and model the payment against the ADU's expected rent.
What is the CalHFA ADU grant?
It's a California program offering up to $40,000 toward an ADU's predevelopment costs, plans, permits, soil tests, and impact fees, with priority for lower-income homeowners. It was renewed with expanded funding for 2026. Funds are limited and program terms change, so check current availability; Ashlar Lending can point you to it as part of structuring your financing.
Do I have to pay impact fees upfront?
Usually not anymore. SB 937 lets you defer most development impact fees until final inspection or certificate of occupancy, rather than paying them at permit application, a real cash-flow help during construction. In addition, ADUs under 750 square feet are exempt from most impact and school fees entirely. Rules vary by city, so confirm locally.
Will an ADU pay for itself?
Often, if the rent exceeds the financing payment. With ADU rents of $1,200 to $2,300 a month in this area and typical returns around 8 to 12% a year, a well-planned unit can cover its own loan and add lasting value. The key is sizing the build and financing to realistic rent, which is exactly the math Ashlar Lending runs with you before you commit.
Thinking about building an ADU in San Bernardino County?
Serve First Realty Inc. is a licensed California real estate brokerage that helps San Bernardino County homeowners understand what an ADU adds, and, with Ashlar Lending, how to finance it.
California DRE# 02133513
ADU-build guides for nearby areas
Or start with the statewide overview: Building an ADU in California: Cost & Financing.
More guides for this area: all San Bernardino County real estate guides.