What design decisions should I keep in mind?

Your first question is: what will the use of this ADU be for? Is it to house a family member? Or am I using it for additional income? That will start the design process and give you a mental framework for what should be included/not included in the ADU.

Your second question should be: what’s my budget for this project? ADU projects fall into a spectrum of cost vs customize-ability. This is a typical depiction of where a project pans out.


The third (and potentially most important question): What will my jurisdiction allow? If you want to build an ADU for your son returning home with his family, and believe a two-story ADU would best fit their needs, your jurisdiction may have a 16ft height limit – limiting your choices.

What type of ADU is right for me?

In this chapter – we will provide a wide selection of choices for you to choose from when deciding on your ADU. Each type of housing has advantages and disadvantages, some may suit you better than others.

What to choose? Stick Built vs Modular vs Tiny Home vs Panelized

There are essentially four types of ADU’s you can build on your property. Stick built (traditional), Modular, Prefab and Panelized. We’ll take you through each one and give examples so you can compare.

Stick Built (traditional)

This is what most people think of when they think of building any type of residential structure. Stick built simply means you will use wood frame construction (known by most contractors) to build your house. This is easily the most customizable because of the flexibility of the build process, but can be quite labor intensive and expensive as you customize more and more parts of the design.

Stick built can be economical in some cases where awkward property types, conservative planning departments, or pre-approved plan sets allow you to spend less on your build. Customized ADU vendors like CottageADU are a great example of these types of homes.

(c) Cottage ADU


Modular housing (also known as prefabricated housing) is typically built to about 80-90% completion in a factory off-site and then installed and assembled on-site. The main difference between a ‘modular’ home and a manufactured home is that manufactured homes are built to the national HUD code, while modular homes are built to all applicable state and local building codes. California Modular LLC is an example of a modular company with plenty of design choices to choose from when building an ADU.

You can see a great video depicting how a modular home is built here.

Manufactured Housing

Manufactured housing is built off-site in a separate location and then transported on-site to be hooked up to utilities.

You have probably heard about BOXABL – a new player in the space who specializes in small manufactured housing. They have created a new ‘folding’ technique to allow for homes to get assembled “anywhere”. Boxabl , though attractive at the price point, does have issues when it comes to building an ADU. Namely, the machines needed to build this type of housing are usually too big to fit into a typical backyard in California. The installation, transportation, permitting, and solar costs will add up and get much closer to a traditional stick-built ADU then they will tell you. But they are cool!

(c) BOXABL Inc.

Tiny Homes

You could technically have a ‘tiny home’ with any construction technique as long as the home is under 400 square feet. That said, in this article we are only going to focus on Tiny Homes manufactured offsite and then delivered onsite. These tiny homes would also be considered manufacturing housing, however we have included their own section because they can also be put on wheels and certified with the same process as an RV.

You will have to know your planning department to confirm your cities acceptance of tiny homes on wheels, but they can be a viable and affordable alternative to other ADU building methods. The downsides here are apparent: they may not give you the space you’d like to have and they aren’t going to add value to your property. Pacifica Tiny Homes is a great example of a tiny house on wheels builder (who provides ADU’s as well!)

A beautiful example of a tiny home on wheels. (c) Pacifica Tiny Homes


Panelized homes are a new type of ADU being built that uses some modular components along with different materials and on-site assembly methods to bring a substantially lower price to an ADU project.

Panelized Homes use pre-finished SIPs (structurally insulated panels) to finish 60% of the build off-site, then assemble SIPs, install Mechanical, Electrical, Plumbing and Solar on-site in 2-3 weeks to finish the project. This new method significantly reduces labor costs because of the time reduction while significantly increasing the energy efficiency of the home because the panels come insulated with high r-value insulation with little leakage. The downside to this type of construction is that you won’t have all the design flexibility of a traditional stick-built as the panels come pre-fabricated.

Our company, ADU.Works, specializes in panelized ADU’s. You can learn more about the build process here.

Two builders install a SIP home.

In the next chapter, we’re going to look at how to acquire permits for your ADU – we hope to take as much anxiety away from this process as possible. Move on to Chapter 4 here.