Berkeley ADU Guide: Costs, Rules, and Where to Get Help in 2026

Berkeley's median home price runs about $1.4 million to $1.6 million, which makes adding an accessory dwelling unit (ADU) one of the most practical ways to create value and income on a lot you already own. In 2026 the rules are simpler than they have ever been: most ADUs are approved ministerially, without a public hearing, and the city must issue permits within 120 days when state standards are met. Here is what homeowners should know before they start.

The rules in plain language

On a single-family lot you may build one ADU plus one junior ADU (JADU). A JADU is capped at 500 square feet and lives inside the primary home, sharing its bathroom. ADUs must be at least 190 square feet, attached units may be up to 50 percent of the primary dwelling, and detached sizes and heights depend on zoning. Long-term rentals are permitted, but short-term rentals under 30 days are not. In July 2025 Berkeley adopted AB 1033 rules that allow the separate, condo-style sale of an ADU, with a tenant right of first refusal.

What an ADU actually costs

Expect roughly $250,000 to $500,000 for a new detached or attached build, $120,000 to $250,000 for a garage conversion, and about $200,000 to $275,000 for a typical 750-square-foot unit. The permit side is friendlier than people expect: zoning plan checks run about $250, neighbor notice about $500, and address assignment about $250, with building permit fees based on valuation. All-in permit costs typically land between $8,000 and $18,000, and roughly half that with a pre-approved plan. Berkeley charges no impact fees and no utility connection or capacity charges on ADUs.

Help that is actually available

The state CalHFA ADU Grant program reimburses up to $40,000 of predevelopment costs, including plans, permits, and soils tests. Berkeley's Pre-Approved ADU Program (under state AB 1332) cuts plan-check costs by 50 percent. And a four-year amnesty program, running since January 2025, legalizes unpermitted units built before January 1, 2020 for reduced fees.

Should you build, or buy a home that has one?

For owners, an ADU changes the numbers on a Berkeley property: rental income can offset the mortgage while you stay put, or a unit can house an aging parent or adult child. For buyers, homes with existing ADUs are increasingly sought after, and they often trade at a premium that reflects the income. Either way, financing options like FHA 203k, HELOCs, and the CalHFA grant make the project more reachable than the headline cost suggests.