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Detached ADUs in Modesto

A separate small house behind yours, built new. Where a free regional plan fits your yard we start there; where it does not, we draw one that does. Licensed and insured.

Check my yard Free regional plans

What counts as a detached ADU?

It is a full second dwelling in its own building on your lot, with a kitchen, a bathroom and a private entry. It stands apart from the main house, so tenants and family each get their own walls.

Can I build one of the free regional plans?

Very likely, if the footprint fits. Stanislaus County and its partner cities, Modesto among them, offer pre-drawn detached ADU plans at no charge, as of October 2026. The county's page lists plan sets of 405, 744 and 1,192 sq ft, and some city pages list more sizes. Details are in our free plans guide.

How close to the property line can it go?

California caps the side and rear setback at 4 feet for a detached ADU of up to 800 sq ft, and a city's front setback cannot block that unit. In 2023, HCD told Modesto that its 15-foot street-side setback could not apply to ADUs. The city adopted an amended ADU code in late 2024.

Does a detached ADU need solar?

Generally, yes. California's energy code applies the solar requirement to most new detached ADUs, and Turlock's submission list asks for photovoltaic plans with every new detached ADU. A pre-drawn plan does not remove this step.

Which costs are unique to new construction?

A new slab or foundation, walls and roof.
Trenching for water, sewer and power across the yard.
Truss calculations where the plan uses engineered trusses.
Solar panels and the energy paperwork that goes with them.

Will I pay impact fees?

Not at 750 sq ft of interior living space or less. As of October 2026, Government Code §66311.5 removes impact fees below that line, and units under 500 sq ft also skip school fees. The 405 and 744 sq ft regional plans both sit under 750 sq ft.

Should I build new or convert the garage?

It depends on the garage. If it is sound, a conversion usually costs less. If it is failing or there is none, a detached unit may be the better use of the money. Where both work, we put both prices in front of you in writing.

Find out if a detached ADU fits

Share the address. We map setbacks, easements and the utility route, and test the free plan footprints against your yard.