Decisions, Decision, Decisions. What to Be Aware of Before Building An ADU.

Building your ADU project from start to finish.

When deciding to build an ADU project, you probably have a number of questions. How does this process work? Who do I contact first? How much does it cost and what are my financing options?

It is a sign of wisdom to ask questions, so you’re doing the right thing. The good news is that at Housable, we’ve done a lot of the legwork for you in illuminating the process. If you commit to learning the rules of the ADU process, you’ll be breaking ground on your project in no time. We prepared this article in order to help you learn more about key professionals to work with, designing and building your ADU, getting financed, and more.

Housable is committed to help you succeed with your ADU project.

Architect + Contractor

Do I need to work with an architect? We hear this question all the time.

The short answer is no, you don’t. But the more complex your project gets, the more likely you will need one. In general, architects can be quite costly, but depending on the project, it may be what's best suited for you. Many homeowners choose to work with an architect and a contractor, who separately manage their project through each step, from initial design to final inspection and occupancy.

The benefit of this model is that you have specialized professionals who are highly capable of managing the two critical phases of any construction project; Design and permitting (architect) and then building and inspections (contractor). The downside is that no one professional has full responsibility for the success of your project, and sometimes contractors and architects have misaligned interests, which may cause project disruption.

For example, an architect may try to design an award-winning piece of architecture and may not prioritize cost reduction. On the other hand, contractors focus on efficiency and buildability and maintaining a schedule. The architect and contractor need to be able to work together and see eye to eye, even if they have different priorities. You are more likely to succeed if you choose an architect and a contractor who have worked together on previous ADU projects and completed them successfully.

The architect-contractor model is great for those who would like a very unique design and are willing to spend a bit more to get it.


Design and build contractors specialize in providing all ADU project services in one package, including feasibility, design, permitting, and construction.

They are a great fit for homeowners who are looking to find a one stop shop for their ADU project.

Design and build is a good option if you are looking for a single point of contact during the process. These contractors tend to be more efficient because they specialize in ADUs and have a straightforward approach.

You should consider working with a design build contractor if you’d like a simple, efficient process that is within a predictable budget.

Prefab/Manufactured Units

The prefab ADU market is growing. They are still only a small fraction of the total annual ADU project, but they have increased in popularity over recent years as a greater variety of vendors emerge.

If you are interested in building a detached unit, prefab ADUs are an attractive option because they are modular units.

It is important to consider a variety of issues when researching whether modular is the right solution for you:

  1. Determine your need for customization. Many neighborhoods in California have design restrictions and require the ADU to be built with the same exterior materials and characteristics as the primary home. This is a deal breaker for many modular manufacturers who have standardized options and feature selections.
  2. Research the building code required in your local area. Many modular units are built to the HUD code, which is a lesser national building code and is not allowed in nearly all zoned residential areas. All ADU units in California must be built and inspected to the California Building Code 2016 and meet all requirements for fire safety and energy conservation. If the model is standardized and pre approved, make sure that its design will be compliant with your local codes using a model spec sheet from the manufacturer.
  3. Prefab is not always cheaper. It is a common misconception that modular units are always less expensive and faster than on-site construction. While this is true in some cases, it should not be assumed. There have been plenty of scenarios where they took just as long as regular construction.
  4. Know who is handling what. You will still need to take care of the necessary permits (which Housable can help with), and hire a local contractor to prepare the site and install the foundation. Ask whether the company has worked in your area before. If so, they may have contractors who can help you estimate the steps of the project which are outside their scope.
  5. In some cases, prefab units may be a great option. They are an interesting alternative to on-site construction.

    Find out whether you are eligible to build an ADU on your property using Housable’s free property check tool.


    Many homeowners start the process assuming they can handle it themselves. After all, ADUs are smaller projects than regular home construction and seem relatively straightforward.

    This is a mistake for many.

    Building an ADU requires time and experience. Do you have enough of either? Are you confident in your ability to manage every step of the project? What is your motivation for DIY? Are you trying to save money or time?

    Beware that doing it yourself will make it much much harder. You may make progress only realizing that you missed critical steps. It's better to be safe than sorry; don’t handle more than you can reasonably take on. It may make sense to hire professional services from the beginning.

    DIY is a great approach if you feel confident that you know what you are getting into, or at the very least, you are willing to accept many risks. If not, we’d highly suggest working with professionals on your project. Housable offers guidance for every step along the way from start to finish.

    Project Financing

    Last but certainly not least, financing. Regardless of which path you take, you will always need to consider how you will pay for the project. You should make financing decisions as early as possible in the process; it will make everything far easier. If you get qualified for financing early, it will help you determine your budget and what your long term returns will be.

    If you’ve dealt with lenders in advance, it will be much easier to deal with architects and contractors later on.

    Read through more resources for ADU financing, designs and regulations in our knowledge base and learn more about your local requirements with our Property Check tool . You can also read more on Financing an ADU.

    Closing the Loop

    As you’re probably realizing, the ADU process includes many steps along the way. There are proven ways to do this, and unless you feel confident developing your own process, it makes very little sense to make it up as you go. There are many risks, as we've mentioned, they can include projects going over budget, dealing with messes from contractors, failure to permit correctly, and a lot more. Sometimes it's worth it to spend the extra money to ensure it's done properly.

    It doesn’t need to be hard though. Housable has done a lot of the work for you through our ADU marketplace, and we help with feasibility, design, and permitting. We also connect you to a contractor or a lender when you are ready.

    If you’re ready to start the ADU process, check out our free property check tool to understand whether you property is eligible for an ADU project.