The answer to the question “How long does it take to build an ADU?” depends primarily on your ADU type. The two primary types you’ll encounter are stick-built and prefab ADUs, and the latter will make your life much easier. Stick-built ADUs come together piece by piece, whereas prefab ADUs – we like to call their process “offsite construction” – are built to preset floor plans. These units go from the factory to your lot in one piece that’s complete on both the inside and outside.
While there are theoretically infinite possibilities with traditional stick-built ADUs, Spacial’s offsite construction process results in a much shorter project timeline. Below, learn all the steps involved in building an ADU – and how offsite construction gets your ADU ready in four to nine months.
Assuming you work with an ADU design company, below are the steps that your ADU must go through before it’s ready for move-in.
Before you sign a contract with an ADU agency, you should look at the company’s floor plans to see how many square feet and bedrooms are available. You should also check for accessibility features which means the ADU can grow with you as your needs change. If you see both, you’ve chosen a reliable builder. You’ll also know you’re in good hands if your contract fully clarifies how all the responsibilities are divided between you and the ADU company. And then, you can sit back and let the ADU firm handle all the hard work.
Before your company starts building your ADU, the team will measure your site and decide which construction methods make sense. This process involves assessing whether the ADU site is flat or sloped (the latter can add some complications).
The process also encompasses determining where and how to connect your water, electrical, and sewer lines. Your team will also determine whether to remove old garages, patches of concrete, and trees (which can sometimes be trimmed instead). Then, your team will figure out where to place the crane – and, just as importantly, where the crane will reach.
Your ADU team will include a contractor and an architect. Both these roles are key to the third step of building your ADU: Researching city and county codes and planning your ADU accordingly. They’ll then put together an ADU plan based on what they see. You’ll get the final sign-off on this plan – this is your chance to ask for changes – before it goes to the city for review.
Your ADU designer will combine all your plans into a package called a permit set. Your city and county regulatory bodies will review this permit set and request changes. For ADU projects in California, you must meet additional energy-efficiency requirements based on the state’s Title 24 legislation.
Your ADU company will entirely handle any required changes – you can take a step back and trust that the process will go according to plan. Once all is in order, you can obtain your official construction permits. Although you’ll likely need to go through both city and county bodies to get proper licensure, your ADU design firm can make that easy.
That’s especially true if you choose Spacial since we deal with all authorities having jurisdiction (AHJ) on your behalf. We’ll submit your plans, answer your city’s questions and respond to their comments, and pick up your permit. We’ll also work with your regional utility providers to receive any required permission.
Doing all this work can feel like a part-time job, and that’s why we include it in our services. And as we make any necessary changes, we’ll start the offsite construction process too. This process happens without any commotion or noise in your backyard and shaves months off your timeline. We’ll tell you all about it when you contact us to share your vision for your ADU.
Once your ADU company makes all the necessary changes, the city will issue a permit. That means your team can start building – that’s a huge step toward your ADU coming to life. Your team will then schedule the contractor and get ready to bring the ADU from its offsite location into your backyard.
Site and foundation preparation is the final big step before your company builds your ADU. Site prep involves clearing obstructions and debris, demolishing any structures that are no longer necessary, and running the utility lines. After that, your ADU builder will excavate your site to receive the foundation. And then, after that, they’ll pour concrete to install your foundation. Around the same time, your water, electricity, and sewer lines get put into place. Think of this step as putting all the puzzle pieces in place.
With your site and foundation set and your offsite construction complete, everything is ready to come together on-site. Some ADU companies can make this happen in just one day. This way, your backyard is noisy and chaotic for as short a time as possible.
Spacial is a great example. Where other companies might assemble your ADU from individual panels, Spacial’s volumetric modular units ship as a singular unit. The crane literally drops them right into place – no need to connect a bunch of modular panels. That’s how we get your ADU into place in literally one day. And when you walk inside, you’ll see complete walls, flooring, and cabinets – there’s only a bit left to do.
For the most part, the interior and exterior of your ADU are complete after your company cranes it into place. That said, your contractor will come in and make some last-minute touch-ups to take your ADU from excellent to perfect. These touch-ups may include removing the sticky coating from your windows and taking the floor covering up. They can also include placing a skirt around the bottom of the unit, adding steps to the unit, and furnishing the unit.
Simultaneously, you may want to make some exterior renovations to truly make your ADU feel like a home. Driveway renovation, patio and sidewalk installation, new landscaping, and more are all on the table.
The final step of ADU building comprises two parts. First, the contractor will obtain a temporary certificate of occupancy (TCO) and give you the keys to your brand-new ADU. After that, your ADU company can furnish your home for you. At Spacial, we do exactly this through our West Elm partnership.
Not long afterward, you’ll receive a final certificate of occupancy (COO). If you’re thinking of renting your ADU, you’ll need to wait until this step to start searching for a tenant. Or if you’re making space for family or friends, you can invite them to start moving in. Everything will be ready to go and feel just like home.
Many ADU companies will present you with a selection of prefab ADUs. These units differ from traditional stick-built ADUs. Below is a more in-depth explanation of each ADU type’s differences.
A traditional stick-built ADU:
A prefab ADU:
Any ADU project – even one as tried and true as an offsite construction unit – can experience delays. The following factors can extend your project timeline.
With the right ADU partner on your side, your unit can be ready in well under a year – sometimes as quickly as four months. Spacial can be that partner if you’re building an ADU in the San Francisco Bay Area. We build studio and one-bedroom ADUs and do all the heavy lifting – including the craning – to get them in place. Plus, our offsite construction means you’ll have far less commotion in your backyard as your ADU comes to life. Contact us today to learn how we can make your dream ADU a reality.