Construct
Get bids and hire a contractor | Understand your role during construction
Project TIMELINE
Most ADU projects take 12-18 months to complete, but some extend to 24 months or more. Construction takes 6-12 months, depending on the size, type, and complexity of your project.
Construction FAQs
Here are a few of the most frequently asked questions about ADU construction. See the content below and our ADU Guidebook for more guidance, resources, and tips for all steps of the process.
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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. Start by asking around your community for recommendations, and use social media like Nextdoor and Instagram to search for local businesses and find examples of their work.
Next, you’ll solicit bids. See our Guidebook for more details on what you want to see in a bid, what other documentation to collect from potential contractors, and what to look for in your bidding candidates. You will want to get at least three bids for comparison.
When you have bids, you can begin selecting your contractor. See our Guidebook for more details on how to compare bids and choose the best option for you.
Before you hire a contractor, make sure to check their license and insurance and when they present you with a contract, review everything carefully. See our Guidebook for more details.
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Site-built/Traditional: A traditionally constructed ADU is designed and built specifically to your preferences and property and built on site (“stick-built”). This option allows for a lot of customization and smaller changes to be made throughout the construction process.
Prefabricated/panelized/modular: These ADUs are partially or mostly built in a factory, then shipped to your site to be put together. Sometimes the company will include all services in their fee (“turn-key”), including help with permitting and all on-site construction tasks (e.g., laying the foundation, utility hookups, etc.). Other times you’ll need to hire additional professionals to help.
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Construction costs for your second unit will vary significantly depending on personal preferences, site conditions, location, and many other factors.
Size: Despite what many think, smaller ADUs may cost almost the same as larger ones. Many costs like foundation, kitchen and bathroom work only increase slightly for larger ADUs. Kitchen costs will range from $25,000–$50,000 with each bathroom ranging from $15,000–$25,000.
Type: New construction, both detached and attached, tend to be the most expensive. Garage conversions are not much cheaper than new construction if at all. Conversions of interior space (basement or otherwise) are often the cheapest.
Other factors:
Quality of interior finish work and amenities
Architectural form and details
Extent of utility, structural, mechanical, electrical, and plumbing upgrades required
Required site upgrades (sidewalks, sewer and water)
Whether sprinklers are required
Whether doors and windows meet emergency exit standards
Lot complexity (slope, trees, fault lines, etc.)
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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
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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 city or utility inspections, it is your responsibility as the property owner to make sure that the inspections are conducted as required.
Building your ADU
Permit in hand, you’re ready to break ground and see your project become a reality! From site preparation to passing your final inspection, you’ll stay in touch with your contractor and make final decisions about project details.
KEEP in mind
Managing the construction process is a complex, constant responsibility, so take serious consideration of any plans to be your own general contractor. If you’re working with a design/build team or have hired a general contractor, they’ll manage the project (including negotiation, payment schedules, quality checks, and working with the City and necessary agencies). Often, people who are their own general contractors have a difficult and unpleasant time.
Hire your contractor
If you are not using a design/build firm, you will need to hire a contractor for the construction phase of your ADU. Start by asking around your community for recommendations, and use social media like Nextdoor and Instagram to search for local businesses and find examples of their work. You can also ask your architect or design team to recommend a contractor they’ve previously worked with. You will use drawings from your designer to solicit 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 Guidebook for many more details on getting bids and hiring a contractor.
Monitor construction
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. Timelines for construction vary, but 6-12 months is fairly common. See more details about managing construction in our Guidebook.
Get inspections
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, exterior finishes, etc.).
It is your and your contractor’s responsibility to schedule all required inspections, which you can do online through the City of Upland’s CSS Portal. Your building permit includes a list of all necessary inspections.
Note: If your ADU is less than 5 feet from the property line and/or if your ADU is close to 750 square feet (the cutoff for impact fee exemptions), the City will require you to provide an official survey of the property and/or the ADU measurements. The City will notify you about this and you’ll need to provide the survey information around the time of your foundation inspection.
If your ADU requires a sprinkler system, be sure to schedule an inspection by the Office of the Fire Marshal before your final inspection by the city, as the city building inspector will need to see verification of their approval.
After your final inspection is approved, the inspector will provide final sign-off on your building permit and then your ADU is ready for move-in!
Building costs
ADU construction costs vary significantly depending on materials, site conditions, location, and other factors.
The cost to build an ADU typically ranges from $30,000 for a simple interior conversion JADU to $400,000+ for a large detached ADU with high-end finishes on a hillside lot. Cost per square foot is a good way to estimate – in the City of Upland this typically ranges from $100-200 per square foot depending on your project. You can use $150 per square foot as a rough average for construction costs (compared to $175 per square foot as a rough estimate of TOTAL project cost).
Despite what many think, smaller ADUs may cost almost the same as larger ones because construction costs are not related to size. Many costs like foundation, kitchen and bathroom work only increase slightly for larger ADUs. Kitchen costs will range from $25,000–$50,000 with each bathroom ranging from $15,000–$25,000.
Visit our Stories to see real-world cost examples for ADUs built in the City of Upland.
KEY Resources for construction
ADU Guidebook
Your comprehensive guide to building an ADU in the City of Upland, from initial inspiration through move-in.
ADU GUIDEBOOk →
Explore the construction process in detail with our ADU Guidebook
Our in-depth guide to building an ADU in the City of Upland, from inspiration to move-in
