ADU construction in Hayward is a very straight forward process. You will have your feasibility meeting, then the building plans are created. Then you will submit it to the city to be reviewed using the E-Permits portal. Finally you will have your ADU built and inspected. The average time frame to complete a freestanding backyard unit is between 8-15 months from initial phone call to keys. A garage conversion moves faster because the walls, slab and roof already exist.
By Ray, Owner & General Contractor · Last updated November 5, 2026
The lot will dictate what type of unit you can have. While both a garage conversion and backyard cottage Hayward are complete ADUs (with their own kitchen, bathroom and entry), the starting point will be very different.
Use this grid to see where each option lands:
ADU type | Size rules in Hayward | CRBA typical cost (2026) | Best fit |
Garage conversion | Existing footprint, no added setback or height limit for the conversion | $120,000 to $220,000 | Detached or attached garages on lots with tight backyards |
Detached backyard cottage | 850 sq ft (studio or 1-bed) or 1,000 sq ft (2+ beds) always allowed; 16 ft tall | $250,000 to $450,000 | Deep lots with rear access and sewer within reach |
Attached ADU | Up to 50% of the main home, with 850 or 1,000 sq ft always allowed | Priced after a feasibility visit | Owners who want family close by with a shared wall |
JADU | Up to 500 sq ft inside the existing home | Lowest of the four | An attached garage or a large bedroom suite |
Why the lot matters in Hayward. Flat post-war lots in neighborhoods like Southgate and Mt. Eden leave room behind the house for a detached unit, as long as the sewer line can reach it by gravity. Hillside parcels in the Hayward Highlands add grading, retaining walls and tougher equipment access. Our earlier post on which garage conversion fits a Hayward home covers the conversion route in depth.
Spacing and power. Hayward requires a new detached or attached ADU to sit at least 6 feet from other buildings on the lot, which rules out some narrow side yards before design starts. New detached units also have to be all-electric, with a heat pump for heating and hot water. On older homes with a 100-amp panel, that means a service upgrade in most cases before ADU construction can start, so we price the panel during the first site visit instead of discovering it at plan check.
Most of the calendar goes to planning, not building. Homeowners ask “how long does an ADU take to plan and build,” and for accessory dwelling unit construction Hayward projects follow the same three stages.
Design and feasibility come first. We check setbacks, utilities and the sewer route, then draw the plans and Title 24 energy report. That takes about one to three months, faster with one of Hayward’s pre-approved ADU plan sets.
City review comes next. Hayward’s ADU process handout commits to a first review in 15 business days and resubmittals in 10 business days. State law also requires the city to act on a complete application within 60 days.
Construction is the last stage. The city’s own handout says 6 to 12 months is common for the build, and a detached unit with new utility lines sits at the long end. New detached ADUs in Hayward must be all-electric, so PG&E service upgrades can add weeks that are outside anyone’s control.
City fees and utility work land on top of construction. Hayward’s handout puts total fees between $6,000 and more than $25,000, with garage conversions at the low end and new detached units at the high end.
Size moves the fee line. ADUs under 750 square feet skip impact fees under state law. All structures over 750 sq ft incur a Park Dedication Fee. Additionally, Hayward Unified School District charges a school fee of $4.79/sf prior to issuing a permit. Therefore, designs that are 740sqft and 760sqft will result in thousands of difference in fees.
Utilities are the other variable. A new water meter, a sewer lateral run across a long backyard or a PG&E panel upgrade can add cost that a headline per-square-foot price never shows. The city’s ADU and JADU permit page lists the current checklist and links to the pre-approved plans gallery.
A permitted ADU does, because it’s a legal second dwelling an appraiser can count. People ask “does an ADU add value to a property,” and the answer turns on two things: the permit and the rent. A unit with a final inspection and a certificate of occupancy can be appraised and rented. An unpermitted conversion adds risk at resale instead.
It helps to look at the rental market. Hayward is located between Oakland and San Jose with BART stations either end of the town meaning your renter pool will include people travelling to and from these towns. A one bedroom unit with a private laundry and entry will compete with these renters.
The flexibility of having the same unit available for your parent, adult child or carer in the future is also key. This is why buyers are paying for this unit. However, build quality is important. Sound insulation, a private entrance and a full kitchen decide whether the unit rents at the top of the market or sits empty between tenants. Our post on why an ADU is a smart Bay Area investment walks through rent and return in more detail.
Look for one license on the whole job, from plans to final inspection. When people search for the best ADU builder near Hayward, the real question is who carries the project through plan check, utilities and inspections without handing it off.
Ask any contractor who builds accessory dwelling units in Hayward for a CSLB license you can check online, a written, itemized quote that shows site work and utilities as separate lines, and photos of finished units. If you’re wondering which contractor near me handles ADU design and build, the answer should be a company that draws the plans, answers plan-check comments and builds with its own crew. That’s how we work as an ADU builder Hayward homeowners can reach by phone at our Jackson Street shop.
Red flags to walk away from:
A lower price up front can cost more over the life of the unit. These are the trades we see most:
Where cheaper wins. If the goal is space for a family member, a JADU or garage conversion inside the existing footprint costs far less than a detached cottage. Our garage conversion service covers that route, and our ADU service page lists every unit type we build. We also build in Castro Valley, San Leandro and Union City.
An ADU built by CRBA as a backyard detached unit will cost approximately $250,000 to $ 450,000, or approximately $400 to $ 650 per square foot. A converted garage unit will cost around $120,000 to $ 220,000. City fees in Hayward will be approximately $6,000 to more than $ 25,000 depending on the size and type of ADU unit.
The minimum size for an ADU in Hayward is 850 square feet for a single bedroom detached unit. Alternatively 1,000 square feet for a double bedroom. The maximum size you can go to is half of the ground floor area of the main house or 1,200 square feet. Detached units can be up to 16ft high and have 4ft side and rear set back. They also need to be a minimum of 6ft from any other buildings.
You start with a planner meeting, then submit plans through Hayward’s E-Permits portal and pay plan check fees. The city reviews in 15 business days and resubmittals in 10, and state law requires action within 60 days of a complete application. After construction and a final inspection, you receive a certificate of occupancy.
Yes. California law allows garage conversions by right, and Hayward can’t require replacement parking for the lost garage. An attached garage can also become a JADU of up to 500 square feet inside the home.
Yes, an ADU can be rented to long-term tenants, and state law lets cities require rentals of 30 days or more. HUD’s 2026 Fair Market Rent for the neighboring Castro Valley ZIP code is $2,460 for one bedroom and $3,000 for two. A unit renting at $3,000 a month brings in $36,000 a year before taxes, insurance and upkeep.
Construction Remodeling in Bay Area
Address: 111 Jackson St, Hayward, CA 94544
Phone: (510) 990-9243
Email: constructionremodelinginbay@gmail.com
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Serving Hayward, Castro Valley, San Leandro, Fremont, Union City and the greater Bay Area. Call for a free estimate, or use our contact page to book a visit.