Prefab or custom ADU? It’s more than just a matter of money. Prefab ADUs are not automatically a better deal than custom-designed accessory dwelling units.

Many homeowners are surprised to learn that the cost is often about the same!

So putting budget aside for a minute, is a prefab ADU the best choice for your property and situation?

1. Will a prefab ADU work on your property?

Lots that are good for a prefab ADU:

  • Flat or gently sloping, easy to make level enough for an ADU.
  • The street is wide enough to accommodate large trucks or cranes.
  • The street is not twisty or up a steep hill that would be difficult for trucks to access.

prefab adu

If your lot has a utility easement, that may also determine whether a prefab is the best choice. On some properties, a garage conversion makes the most sense given easements and other conditions. A Maxable Site Evaluation will include easement, overlay, and other info specific to your property.

2. What is the purpose of your prefab ADU?

Will you need universal design to accommodate someone with a disability and enough room for a ramp?

Will you need a specific floor plan in order to have privacy from the main house, so you can rent the unit?

Are you trying to squeeze as many bedrooms as possible into the footprint?

It’s very possible you’ll find a prefab ADU that will meet all your requirements, but make a list of everything you want so you can cross-check it to the available prefab designs.

Remember, the distance from the factory to your property will impact the cost of transportation. Read this deep dive into prefab costs before you talk to prefab companies.

3. Do you want to minimize construction noise and disruption?

A prefab ADU is the best choice for keeping dirt, noise, disruption, and construction crews to a minimum. Many prefab ADUs are constructed entirely at the factory and installed in only a few days.

Your site will still need to be prepped for the ADU, but that process is brief compared to the months-long construction schedule of a stick-built ADU.

Site prep includes things like:

  • Demoing structures that need to be removed to make room for the ADU, such as a garage or shed.
  • Removal of trees that are in the way of the proposed ADU.
  • Leveling the site and in some cases having a soils engineer approve it.
  • Trenching for water and sewer.
  • Filling a swimming pool that’s on the proposed site.
  • Pouring a concrete foundation.

4. Do you have neighbors who might object to the construction of an ADU?

Let’s say you’re fine with having an ADU built on your property. You’re looking forward to watching it take shape! But what about your neighbors?

Maybe there’s someone nearby with a serious illness or a family who is home-schooling their kids. Months of noisy crews, power tools, and banging hammers could be really hard on them. Most construction crews start work very early in the morning.

Or you might live next door to people who have a history of being difficult. We hope not, but it does happen.

Preparing the site for a prefab ADU will probably take a few weeks, and installation of the unit can happen in as little as a few days. That’s far less than the three to six months of construction typical of stick-built ADUs. Prefab ADUs are definitely easier on the neighbors.

If you do decide to go the stick-built route, here are some handy tips to stay on your neighbors’ nice list.

5. Are you comfortable with a limited number of choices in floor plans and finishes for your ADU?

Even “customizable” prefabs offer only a specific number of options. If you want a lot of say in the design of the floor plan and the interior and exterior finishes, a prefab ADU might not be ideal.

But before you cross prefabs off your list, take a careful look at what the companies have to offer.

Most prefab companies hire talented architects to design ADUs that they hope will appeal to thousands of homeowners. They usually offer studio and one- or two-bedroom floor plans. They’re aiming to please!

The floor plans, roofing, and finishes might be very close to what you would have selected on your own. It’s worth your time to check out the websites of prefab companies and visit the factories and model homes of those you like.

6. Are you in a hurry to get the ADU completed?

There’s almost no way a stick-built ADU can compete with a factory-built unit in terms of timeline.

Even if you’re working with an experienced ADU designer and a general contractor who hires reliable subcontractors, you still need to deal with numerous on-site city inspections and possible weather delays.

However, “trust but verify” is a good motto when it comes to a prefab company’s promised timeline. Look into their track record, ask about their work and materials backlog, and research their reputation. Get references!

7. Do you want to avoid stress and uncertainty?

The past couple of years have been a hard lesson in uncertainty in nearly every aspect of life. Prefab ADUs usually offer a more predictable experience than custom ADUs.

Installing a prefab ADU tends to be less stressful than living with construction in your backyard and the revolving cast of contractors, tradespeople, and inspectors that are involved.

This isn’t to say there are never delays with prefab ADUs. Prefab companies have to maintain employees and manage materials just like every builder does. But there will probably be fewer glitches than with a traditional build.

Make sure to talk with the prefab representative about realistic build timelines, and get the names of past customers you can call and interview about their experience with the company.

Still unsure about custom vs. prefab ADU? Call Maxable!

Our ADU experts have worked with hundreds of homeowners like you. They have insights you may not have considered, as well as the feedback of all those other folks who have taken the plunge and built an ADU.

Our Prefab ADU Partners are some of the most experienced in the business. And if you decide you’d rather go with a custom accessory dwelling unit, we’ll be happy to connect you with one of our local Design Partners.

Maxable is California’s leading ADU marketplace. After writing state laws, educating thousands of homeowners, and completing hundreds of Site Evaluations and ADU projects, we know accessory dwelling units better than anyone! Get in touch when you’re ready to explore your ADU options, from prefab to custom to garage conversion. It all begins with a free ADU Planning Phone Call. Talk to you soon!