ADU Builders

Many properties in California qualify for some type of an ADU, but the answer depends on your lot, zoning, existing structures, wall setbacks, utilities, fire access, easements, and your local city requirements. Detached ADU is usually easier and faster to get permits for, especially if it’s small, standard, or uses pre-approved plans. Detached, attached ADUs, conversions and additions – all have different requirements, that also vary by city, so it is important to check all possibilities individually.

Yes, ADUs can be used as long-term rental housing. California does not generally allow ADUs to be used as short-term rentals. For example, San Jose states the minimum rental term for an ADU is 30 days, including Airbnb rentals. Before planning an ADU for income, confirm the current rental requirements in your city. If rental income is the goal, it is also important to think through privacy, parking, utility access, sound control, storage, and long-term maintenance before building.

An ADU can increase property taxes, but not too much, since it doesn’t trigger a full reassessment of your existing home. In California, the new ADU or new construction portion is typically assessed separately and just added to the existing assessed value of the property.

Example: Current market value of whole property: $1,800,000
But you bought the house decades ago, so current assessed value for taxes: $600,000

Then you build an ADU. The assessor does not say: “Now the whole property is worth $2,000,000, so we will tax the whole thing at today’s value.” Instead, the assessor looks at the new portion – the ADU – and adds it to the existing tax base.

Example: Existing assessed value: $600,000
New ADU assessed value: $200,000
New total assessed value: $800,000

So your taxes will increase a bit but won’t jump violently. The exact tax impact depends on the value of the improvement and your county assessor’s calculation.

Yes. A legal ADU requires permits, plan review, inspections, and code-compliant construction. Depending on the project, the city may review zoning, setbacks, structure, fire safety, will have energy, electrical, plumbing, sewer, drainage, ventilation safety and quality requirements. Even smaller JADU or interior conversion projects must be permitted if it is being turned into a legal living unit.

In San Jose and nearby Bay Area cities, a simple interior conversion or JADU may start around $80,000–$150,000, while a garage conversion ADU often falls around $120,000–$200,000+, depending on the existing garage condition and required upgrades.

Attached ADUs commonly require a larger budget, often around $150,000–$300,000+, because they may involve additions, structural work, utilities, kitchen and bathroom construction, roofing, exterior work, and finish installation. Detached ADUs are usually the most expensive option because they are essentially small new homes. A standard detached ADU in the Bay Area may fall around $250,000–$450,000+, and larger or higher-end detached units can go above that.

There’s no “right budget”. Final cost depends on multiple factors. ADUs under 750 sq. ft. may avoid some impact fees, but permits, plans, engineering, utilities, and inspections still need to be included in the budget.

So, How to plan the budget? First – identify the what type of ADU fits your property. Then ask few local contractors to estimate the actual site conditions, square footage, the scope of labor and give you the realistic ballpark figure for labor, materials, for city permit, for engineering/ architectural plans. Be caucious if they give you exact cost immediately, without plans ready and approved by the city – after this new important info and details their price may increase later in the middle of the project.