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An ADU is the most valuable thing most Bay Area homeowners can build on land they already own. Here’s when it’s the right move:
Not sure your lot qualifies, or whether a detached unit, a JADU, or a garage conversion is the right path? Call (510) 990-9243. We’ll ask about your lot, setbacks, utilities, and goal, and tell you honestly which option fits — and roughly what each costs.
Six ADU paths, each suited to a different lot and goal.
A standalone dwelling in the backyard — full kitchen, bathroom, living space, and private entry, typically 400–1,200 square feet. The highest rental value and the most privacy for family. We handle foundation, framing, utility trenching from the main house, and every inspection.
A smaller unit created within the existing home’s footprint — often a converted bedroom or portion of the house with an efficiency kitchen and its own entry. Lower cost and faster permitting than detached construction, with fewer utility requirements. A strong first step for family housing.
Converting an existing garage into a legal ADU is often the fastest and least expensive path to a rentable unit, because the foundation, walls, and roof already exist. Full details on our garage conversion page.
A unit built onto the existing house with its own entrance — sharing a wall but not a doorway. Useful on lots where a detached structure won’t fit setbacks, and often cheaper for utilities than a detached build. Related: room additions.
Before you commit: lot feasibility analysis (setbacks, coverage, utilities, easements, fire access), architectural plans, structural engineering, and Title 24 compliance, prepared and submitted with plan-check responses handled. The stage where DIY ADU projects most often stall.
The unglamorous work that decides whether your ADU is legal: city submittal, plan check, sewer and water connections, electrical subpanel and metering decisions, gas where applicable, and every required inspection through final sign-off.
Don’t see your project? Call (510) 990-9243— we handle it all.
Call (510) 990-9243. We ask lot size, where the utilities run, whether there’s a garage in play, your target unit size, and whether it’s for rent or family. From that we can usually tell you which ADU type fits and a working cost range.
Free on-site feasibility visit: setbacks, lot coverage, utility locations and capacity, panel size, sewer access, grade and drainage, fire-access requirements. Then plans and structural drawings, and a written itemized quote — plans, permits, site work, utilities, construction, finishes, timeline — before submittal.
We submit and manage plan check. Then site work and foundation, framing, utility trenching and connections, rough trades, inspections, insulation and drywall, kitchen and bath, finishes — through final inspection and certificate of occupancy where required. You end with a legal dwelling you can rent, house family in, or count in an appraisal.
Realistic timeline:
Feasibility and plans 1–2 months
City permitting 2–5 months in most Bay Area cities
Construction 4–8 months for detached, less for JADU/conversion.
Total commonly 8–15 months from first call to keys.
On prefab and modular ADUs: they advertise a lower headline price, but that price rarely includes site work, foundation, utility connections, permits, delivery, or crane placement — which is where a large share of ADU cost actually lives. We build custom because it fits real Bay Area lots, but we’ll give you an honest comparison at your feasibility visit rather than a sales pitch.
What you won’t pay for:
Call (510) 990-9243 with your lot size and what you want to build.
ADU quotes vary more than almost any residential project, because half the cost is invisible — site work, utilities, and permitting rather than the building itself. Our structure:
Phone range first. Unit type, target size, and where utilities run gets you a working range on the call.
Free feasibility visit and written quote. No fee. And if your lot genuinely can’t support the ADU you’re imagining, you’ll hear it at the visit — before you’ve spent anything on plans.
Six things drive the price on a Bay Area ADU:
Based in Hayward, building ADUs across the East Bay and South Bay:
Core service area: Hayward · Castro Valley · San Leandro · Fremont · Union City · San Jose
Also serving: Oakland · Los Gatos · Los Altos · Palo Alto · Mountain View · Sunnyvale · Cupertino · Santa Clara · San Francisco
In 2026, a detached new-construction ADU in the Bay Area typically runs $250,000–$450,000, or roughly $400–$650 per square foot. Garage conversion ADUs are less expensive at $120,000–$220,000, and JADUs within the existing home start around $90,000. A large share of ADU cost is site work, utilities, and permitting rather than the structure itself.
Plan on roughly 8–15 months total: 1–2 months for feasibility and plans, 2–5 months for city permitting, and 4–8 months of construction for a detached unit. Garage conversion ADUs and JADUs are faster on both permitting and construction.
An ADU is a fully independent dwelling with its own kitchen, bathroom, and entrance — detached, attached, or converted from existing space. A JADU (junior ADU) is smaller and created within the existing home's footprint, with an efficiency kitchen and separate entry, and may share a bathroom depending on current requirements. JADUs cost less and permit faster; full ADUs rent for more.
Yes — renting is the most common use, and a permitted ADU can be rented long-term throughout California. Short-term rental rules (under 30 days) vary significantly by city and many Bay Area jurisdictions restrict them. Renting requires that the unit be permitted and signed off; unpermitted units can't be legally rented. Check your city's specific short-term rental ordinance.
Both. A permitted ADU adds appraisable square footage and rental income potential, which typically increases property value. It also triggers a California property tax reassessment — but only on the new construction's value, not the whole property; your existing Proposition 13 basis is preserved. Your county assessor can estimate the increase.
Prefab units advertise lower base prices, but those figures typically exclude site work, foundation, utility connections, permits, delivery, and crane placement — costs that often close most of the gap. Prefab can be faster and works well on flat, accessible lots; custom construction fits irregular Bay Area lots and matches your existing home. We'll give you an honest comparison at feasibility rather than pushing one path.
Often no. California has substantially limited when cities can require replacement or additional parking for ADUs, particularly near transit. Requirements depend on your location and the type of ADU. We confirm your city's current rules during feasibility, before plans are drawn.
Size limits depend on state law, your city's ordinance, your lot, and whether the unit is detached, attached, or a JADU. Detached ADUs in most Bay Area cities can reach 800–1,200 square feet, with JADUs limited to a smaller footprint. Setbacks, lot coverage, and height limits also constrain the envelope — all verified at feasibility.
Most single-family and many multifamily lots in California can accommodate some form of ADU, but feasibility depends on setbacks, lot coverage, existing structures, utility access, fire access, and easements. Some lots support only a JADU or garage conversion rather than a detached unit. That's exactly what the free feasibility visit determines.
Yes — feasibility, architectural plans, structural engineering, Title 24, city submittal, and plan-check responses are all part of the project, through final inspection and certificate of occupancy. If you have plans already, we build to them.
Yes, with engineering. Sloped Bay Area lots require additional foundation design, retaining, and drainage work, which adds cost but rarely makes an ADU impossible. Soil conditions and grade are assessed at feasibility so the quote reflects the real site.
Build an ADU if you want rental income, a fully independent space for family, or separate legal square footage. Build a room addition if the new space needs to be part of the main house — a primary suite, extra bedrooms, or a larger kitchen. Many homeowners price both; the answer usually comes down to whether independence or connection matters more.
Read all our verified reviews on Google before you decide.
Detached ADUs, JADUs, garage conversion ADUs, and attached units across Hayward, Fremont, San Jose, Oakland, and the Bay Area. Feasibility, plans, permits, utilities, and inspections handled by a licensed general contractor. Free on-site feasibility visit and written itemized quote.
