Bring your San Mateo County ADU vision to life with Revival Homes!

Building an ADU is not an overnight process — planning, permitting, and construction each take time. We advise our clients to budget roughly one year from start to finish — however, some projects can reach completion in as little as eight months! Here are the major project milestones (which you can view in more detail HERE)

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• Project Planning (1 month): If you are starting from scratch, we’ll meet with you and help you quickly develop a custom project scope, floor plan, and construction estimates from three of our trusted partner builders. By the end of this stage, you’ll have a clear sense of what you can build, what it will look like, and how much it will cost. 
• Design (1-1.5 months): With a project scope finalized, we’ll create a full set of architectural and engineering plans (a “plan set”), which we then submit to the city for approval. Along the way, we share your plans with our partner builders to assure that your project design remains on budget. 
• Permitting (2-2.5 months): Once the permit application has been submitted, your city or county’s building department reviews the plans and requests any necessary revisions. Other city agencies, like the department of engineering or your electric utility, may also need to review and approve the plans. We coordinate this process with our architect and engineer to make all required revisions to the plans and get your permit approved as swiftly as possible. We have more details on the permitting process here.‍‍
• Construction (4-8 months): Once your building permit is approved, construction can begin! If you’ve selected a Revival Partner Contractor, they’ll plan accordingly to mobilize as this milestone approaches to capture valuable time. Revival works with our partner contractors to oversee the construction process, which includes site prep, building the foundation, erecting walls and a roof, installing plumbing, electrical, and HVAC, putting in insulation and drywall, and installing finishes and fixtures. Finally, the city will inspect the ADU and issue a certificate of occupancy, which means that the ADU is ready to be lived in! Overall, construction duration depends upon the size of your project, complexity of the build, and time of year.

The cost of building an ADU varies and depends on many project-specific characteristics. The construction costs for our projects have ranged from $115,000 (a 400 square foot garage conversion) to $345,000 (a 1,200 sqft ADU with 3 bedrooms and 2 baths). The cost of construction depends on factors like:

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• Size of the ADU
• 1 or 2 story ADU
• New construction or conversion of existing space
• Level of fixtures, finishes and appliances
• Unique architectural details (vaulted ceilings, custom windows, etc)
• Quality of access to the construction location
• Existing utility capacity - whether the existing panel and sewer connection require upgrades
• Whether you’re building on flat or sloped ground
• Whether demolition and removal of existing structures or hardscape is required

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When you book a free consultation with a Revival Homes ADU expert, we’ll provide a preliminary project cost estimated based upon our first conversation. When you proceed with our Project Planning Package, we’ll provide you with a clear and accurate budget based upon your custom project scope and construction estimates from three of our partner ADU builders.

At one time, the California Housing Finance Agency (CalHFA) offered an ADU Grant Program. The program reimbursed eligible homeowners up to $40,000 in pre-construction expenses that they'd already incurred on their ADU project. This typically included the cost of architectural designs and permitting fees, not actual construction.

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Unfortunately, the grant program is no longer active — all of the funding was fully allocated in 2023. We're actively monitoring the program in case the state provides future funding to the ADU Grant Program.

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Some cities and counties offer ADU funding resources through local programs. We recommend inquiring with your local Planning Department.

The number of ADUs that you can build on your property depends on whether it is a single or multi-family property:

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• Single-family: One full ADU (attached or detached) and one junior ADU (conversion of existing space). Some cities allow more than one full ADU at a one-family house under certain conditions.
• Multi-family: As of 2025, you can build up to the same number of detached ADUs as the number of existing units (up to 8). You can do so in open space or “non-livable space”, like a laundry room, garage, or carport. 

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Our experts can help you verify the number of ADUs that you may build at your property, and recommend different approaches to maximizing the ADU potential of your property!

Yes! Revival Homes provides an in-person site meeting with one of our ADU experts as part of our $299 Project Planning Package. We’ll meet with you to survey your property and discuss your project vision, which we’ll then quickly translate into a customized project scope, design, and construction cost estimates from our partner ADU contractors. 

This depends on your city’s local regulations of short-term rentals. Many cities in California strictly limit your ability to rent an ADU on a short-term (less than 30 days) basis. We recommend that you research your city’s short-term rental regulations during your initial project planning. Our blog post here has additional information.