Financing an ADU with a HELOC

An accessory dwelling unit can house family or earn rent. It's also the largest project most homeowners take on, so financing matters.

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Rent can carry much of the payment

If the unit rents for $2,200 a month, rent covers the 20-year payment with room for taxes, insurance and vacancy. Lenders usually won't count future ADU rent to qualify you for the HELOC itself, so qualify on today's income.

The equity problem

A HELOC is based on the home's current value. An ADU adds value, but only after it's built. If 85% of today's value minus your mortgage falls short of the budget, compare loans that lend on the after-construction value.

Plan for a long build

• Permits and plans can take months before construction starts. Interest only accrues once you draw.
• Budget a 10% contingency; utility connections and site work often surprise.
• Get the builder's payment schedule in writing and match draws to inspections.

What an ADU costs

A garage conversion is usually the least expensive path, often $80,000–$200,000 in California, because the structure and foundation already exist. A detached new-build ADU commonly runs $250,000–$450,000 or more once design, permits, utility connections and impact fees are included. Prefabricated units can shorten construction time but still need a foundation, utilities and site work.

How rent changes the math

Suppose a $200,000 ADU on a HELOC at 7.75% APR. On a 20-year payoff, the payment is about $1,642 a month. If the unit rents for $2,400 a month, rent covers the payment with room for maintenance, vacancy and the higher property tax. Lenders may count part of the expected rent toward your income on a new loan once you have a lease and a history of receiving it, but most HELOC lenders qualify you on your current income, before the ADU exists.

California rules that help

• State law lets most single-family lots add an ADU and a junior ADU, and limits how strictly cities can restrict them.
• Cities must approve or deny a complete ADU application within 60 days.
• Impact fees are waived for ADUs under 750 square feet.
• Owner-occupancy requirements for ADUs have been loosened; check your city's current rules.

Property tax goes up only for the value the ADU adds; the rest of your home keeps its existing assessed value under Proposition 13.

If equity won't cover it

A HELOC lends against today's value. If you need more than your equity supports, compare a construction-to-permanent loan or a renovation mortgage, which lend against the value after the ADU is built, and a cash-out refinance if your current rate is close to today's rates. Construction loans · HELOC vs. renovation loan.

Questions people ask

Will an ADU raise my property taxes?

Usually, yes. An ADU is assessed as new construction and added to your property's value. In California, under Proposition 13, only the value the ADU adds is reassessed; the rest of the home keeps its existing assessed value. Check your county's rules.

Can I do a garage conversion instead of a detached ADU?

Yes. A garage conversion often costs far less than a detached ADU, often $80,000–$200,000 in California versus $250,000–$450,000 or more, so it may fit within a HELOC more easily.

ADU planning checklist

• Confirm your lot's ADU rules with the city: size, setbacks, height and parking.
• Get a feasibility review for utilities: sewer capacity, water, electrical panel.
• Decide between conversion, attached and detached.
• Get design and builder bids, including impact and connection fees.
• Check how the ADU affects insurance and property tax.
• Line up financing before plans are approved, so construction isn't delayed.

Also asked

Can I rent out a junior ADU separately?

Usually yes. A junior ADU is a smaller unit within the main home, with its own entrance and a basic kitchen. California rules generally require the owner to live in either the main home or the junior ADU, which differs from detached ADUs. Check your city's current rules before planning rental income.

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