Phase Six
Construction
- Get bids
- Hire a contractor
- Understand everyone's roles during construction
Project timeline
The Construction phase typically takes 6-12 months. Most ADU projects take 12-18 months to complete, but some extend to 24 months or more.
Step-by-Step
Hire Your Contractor
Construction Step 1
If you are not using a design/build firm, you will need to hire a contractor for the construction phase of your ADU. Often, people who are their own general contractors have a difficult time. Building an ADU is more like building an entire home than a renovation. A professional team will manage the project, including contract negotiation, payment schedules, quality checks, and working with local departments and staff and other agencies. While it may cost more up front, you might save a lot of money by reducing delays or change orders, and get your ADU rented sooner too.
You will use drawings from your designer to get bids from contractors and make sure you are specific about what you want each bid to include (license details, insurance information, examples of past work, etc.). Your design team may be able to help you with this.
It’s a good idea to select between at least three bids, and it’s okay to ask contractors clarifying questions about their bid. Your designer may be able to help you compare the bids. It’s a good idea to reach out to references and to consider your personal interactions with the contractor – you’ll want to feel like you work well together and that they understand your goals.
See our free ADU Guidebook for more details on hiring a contractor.
Key Resources
Monitor construction
Construction Step 2
Once you have building permits, the contractor you hire will lead the construction of your ADU. Be sure you have all funding in place before you start construction.
Communicate frequently with your contractor to make decisions about fixtures and finishes as needed and verify progress before making payments. Schedule a weekly check-in meeting with your contractor to stay up to date on the progress and any changes to the schedule or budget.
Get Inspections
Construction Step 3
During construction, your ADU will be inspected multiple times to ensure it is being built according to the permitted plans (typical inspections include foundations/footings, framing, electrical/plumbing, and exterior finishes).
Many Building Departments have online portals or direct phone numbers for scheduling inspections. Generally, it is your and your contractor’s responsibility to schedule all required inspections. For a list of inspections and how to schedule, contact your Building Department. After your final inspection is approved, you may be issued a certificate of occupancy. Your ADU is ready for move-in!
Frequently Asked Questions
Here are a few of the most frequently asked questions about construction. See the content above for more guidance, resources, and tips for all steps of the process.
How do I find a contractor?
If you are not using a design/build firm, you will need to find a contractor to take over for the construction phase of your ADU.
First, you’ll solicit bids. You will want to get at least three bids for comparison.
When you have bids, you can begin selecting your contractor.
Before you hire a contractor, make sure to check their license and insurance and when they present you with a contract, review everything carefully.
How much does construction cost?
Construction costs (also called “hard costs”) for your ADU will vary significantly depending on personal preferences, site conditions, location, and many other factors. Hard costs typically total around 85% of your total project budget.
See the Budgeting and Finance page for more details and visit our Stories to see real-world cost examples for ADUs built in San Mateo County. Also check out our ADU Calculator to create a construction cost estimate based on your location.
How long does construction take?
Traditional construction will take 6-12 months, though this will vary depending on the specifics of the project. Stages of construction include:
- Site preparation: 1-2 months
- Foundation: 1 month
- Walls, roof, doors: 1-2 months
- Plumbing & electrical: 1-2 months
- Insulation & drywall: ½-1 month
- Fixtures & finishes: 1-2 months
- Final touches: ½-2 months
What are my responsibilities during construction?
While your contractor will lead the construction process, you will have the following responsibilities:
- Keep in touch with your contractor and set up a schedule for checking in.
- Regularly walk through the construction area to monitor the quality of the work and make sure the work is progressing the way you expect.
- Be prepared to make decisions about the details—light fixtures, appliances, and other materials—in a timely manner so your contractor can stay on schedule.
- Follow the contract you agreed to, including any changes as described specifically in a change order form.
- Although your contractor will usually arrange the required inspections, it is your responsibility as the property owner to make sure that the inspections are conducted as required.
Build your adu with confidence
Learn how to hire a contractor and your role during construction
