Square footage that follows the property
A permitted, inspected unit is on record with the county. It raises what your property is worth and what it can earn, and it is there when you sell.
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The numbers
A 500 sq ft detached unit, standard finish. Payback counts rent only; the value added to the property is on top. Change every assumption in the calculator →
500 sq ft detached, standard finish, including design, engineering and construction.
Fully financed at 7.75% over 20 years.
Years of net rent to cover the project cost, before any value added to the property.
Where the value comes from
Permitted and on record
Unpermitted space is discounted or ignored by appraisers and lenders. A permitted unit is counted, insured and financeable.
Taxes on the addition only
Building an ADU does not reassess your whole property. The county adds the new construction's value to your existing base.
More →Income, if you want it
A unit built for value can still be rented. A licensed broker on the founding team can place the tenant when the time comes.
More →The rules that matter here
State law, which no city can go under. Full guide →
Sold separately, sometimes
Under AB 1033 a city may allow an ADU to be sold as a condominium. Some Santa Clara County cities have opted in.
No impact fees under 750 sq ft
Prohibited below 750 square feet, proportional above it.
Ministerial approval
Reviewed against an objective checklist, no hearing, no discretion, so the value is not hostage to a board.
A 60-day decision
The city has 60 days on a complete application, 30 with a pre-approved plan.
Plans that fit
Questions this comes with
From the 2026 HCD handbook. All answers →
Does an ADU actually add value?
It adds permitted, on-record square footage that follows the property, which is a different thing from a renovation that only changes how the house feels. Beyond resale, the common reasons our clients build are rental income against a mortgage, room for aging parents or adult kids who need to be close but not in the house, and a dedicated office or studio.
Brad is a licensed Real Estate Broker with ten years helping investors, so the conversation about what the unit adds in income and long-term value is one we have properly rather than hand-wave.
Will building an ADU reset my property taxes?
Not on the whole property. Under Proposition 13, adding an ADU triggers a reassessment of the new construction only — the assessor adds the value of what you built to your existing assessed value. The original house keeps its existing base year value and is not reassessed.
The county assessor is the authority on your specific bill, and it is worth a call to them before you plan around a number. Brad can walk you through how the arithmetic usually shapes up against the rental side.
Can I sell the ADU separately from my house?
Only if your city has opted in. By default an ADU cannot be sold separately. A city may adopt an ordinance allowing the primary dwelling and the ADU to be sold separately as condominiums, but that requires the city to act — it is not automatic.
San José is the notable local example. Worth asking about specifically if separate sale is part of your plan, because it changes the financing and title picture substantially, not just the paperwork.
How much does an ADU cost?
The honest answer is that we do not quote a price without seeing the property, and we will not give you a cost-per-square-foot number over chat. Two lots on the same street can differ by a lot once utility runs, grade, access, and the condition of what is already there come into it, and a number pulled from a blog is not a quote.
What we will do is give you a real number after the free site walk, with the scope written down. Bayfront's model is fixed scope and fixed schedule, with no change-order surprises — which only works if the number is built on an actual look at the property.
If you want to work the numbers yourself in the meantime, the feasibility calculator gives you a cost range, the monthly payment, and whether the rent covers it, with every assumption adjustable.
Find out what your lot is worth with a unit on it
A free site walk and feasibility check. So you can have a straight & honest answer.