ADU vs. Tiny House: What’s The Difference?

May 23, 2022

Compact, fewer rooms, smaller plot of land: On the surface, there seems to be no difference at all between ADUs and tiny houses. While they’re both widely regarded as an attainable solution to the national housing shortage, there are still quite a few differences between these two dwelling types. Keep reading to learn the differences between an accessory dwelling unit (ADU) and a tiny house, particularly as those distinctions affect their construction in California.

What is an accessory dwelling unit?

An ADU – short for “accessory dwelling unit” – is secondary housing fully separate from the main home on a property. ADUs are equipped with their own private entrances and must include a living space, eating space, sleeping space, bathroom, and kitchen to meet the definition of an ADU. You may see ADUs referred to as backyard cottages, granny flats, or casitas.

The umbrella term ADU covers a vast array of options. These options include attached ADUs, conversions such as garages or basement apartments, and detached ADUs (DADUs). The latter describes any ADU built without a connection to the main building or buildings on a residential property.

What is a tiny house?

A tiny house is precisely as it sounds: It’s a very small house, often no more than 400 square feet in size, excluding any loft areas. This type of dwelling is affiliated with the tiny house movement, which advocates for downsized living with fewer possessions in smaller spaces. 

Tiny homes typically contain many of the same components of a regular house, including living space and some form of kitchen facilities. Most models have bathrooms within their living quarters, but others have bathrooms separate from the house itself. Some tiny house models are on wheels, called THOW for short, and can be transported.

Notably, there’s a difference between a small house and a tiny house. Dwellings with between 400 and 1,000 square feet of living space are considered small homes. Tiny homes are under 400 square feet and can often be even smaller than that.

The 10 ways that ADUs and tiny houses differ

If you’re using the terms ADU and tiny house interchangeably, you may be surprised to learn just how different these two dwelling types are, both in definition and in function. These 10 major differences can help illustrate precisely the ways these two housing types stand apart.

1. Size

ADUs are often much larger than tiny homes. The average size of an ADU in California is 615 square feet, and they can be significantly larger. Their size depends on the design and location of the ADU as well as the number of bedrooms. Tiny homes, on the other hand, cannot be larger than 400 square feet. Once they cross that threshold, they are considered “small homes.”

A little barn in the woods
Photo by Arwin Basdew on Unsplash

2. Lot type and use

ADUs are meant to be built on preexisting lots with single-family homes already built on them. They make use of idle backyard space, convert an existing structure on the property, or add square footage to the main home. Tiny homes can be built on any plot of land zoned for residential use, but they are not built on lots where a residential home already stands.

3. Mobility

ADUs are built to stay put. A foundation is poured, and the home is built (or, in Spacial’s case, craned into place) atop that foundation. Tiny homes can be permanently placed on a foundation, or they can be placed on wheels. These mobile versions of tiny homes are hitched to cars and toted around, freeing owners from the need to settle on a single plot of land.

4. Regulations

Both ADUs and tiny homes are legal in California to some degree, but they are guided by different laws and standards.

The standards for tiny homes are set out in Appendix Q of the International Residential Code, which the state of California adopted in 2020. Appendix Q lays out minimum standards for tiny houses. The state has required all jurisdictions to devise their own regulations regarding tiny homes. Additionally, tiny homes on wheels may not be legal in all jurisdictions. In these cases, a tiny home may fall under recreational vehicle restrictions and may not be legal in all places.

For ADUs, California has clear rules that guide the ADU building process. These required standards regulate size, minimum ceiling height, and similar guidelines. Additionally, many major metropolitan areas, including San Francisco and other Bay Area cities, have developed their own guidelines for allowing ADU construction. Check with your local planning and zoning authorities before constructing an ADU or tiny home.

5. Carbon footprint considerations

In many ways, an ADU and a tiny home are similar when it comes to their carbon footprints. As new constructions, both housing types would be required to adhere to environmental standards as set forth in California law. These smaller homes would also inherently consume fewer resources such as water and electricity. When it comes to tiny homes on wheels, though, some of these carbon footprint considerations may be affected. A home that needs to be moved is not often built to the same energy efficiency standards as permanent housing.

Person holding a small leaf
Photo by Nils Stahl on Unsplash

6. Incentives

In California specifically, you’ll find incentives for constructing and financing ADUs, but no such programs exist for the construction of tiny homes. The California Housing Finance Agency (CalHFA) operates an ADU grant program that reimburses up to $40,000 in predevelopment costs for qualified builders. No such incentive program exists for tiny homes in California.

7. Design

The goal of a tiny home is to live in a compact space. In just a few hundred square feet, a tiny home will have all the essentials. An ADU may be smaller than the average home, but it doesn’t feel compact. Instead, ADUs like Spacial’s studio and one-bedroom units are designed with smart storage solutions, bright and airy layouts, and modern aesthetics that make the space feel much larger than it is.

8. Use and purpose

Tiny homes, by virtue of their size, can be quite limiting in how they’re used. They’re ideal for only one person, maybe two people in certain circumstances. ADUs, with fewer limitations on their space, can open up many more use cases and opportunities. These more spacious properties are more likely to appeal to renters, meaning they can earn you passive rental income. They can also be used as office space, creative space, or a backyard getaway.

9. Ease of resale

Tiny homes are considered a niche market. Even those who want to pare down their belongings and live a minimalist lifestyle may find the sub-400 square foot space too cramped for comfort. When it comes time to sell your property, you may have difficulty finding a buyer who shares in your vision for a tiny home.

On the other end of the spectrum, ADU growth shows no signs of slowing down. These homes are widely seen as the future of affordable living in high-cost regions like the Bay Area. They offer benefits for both the dweller and the builder who rents it out or uses an ADU for their own purpose. As awareness and growth continue, you’ll have an easier time convincing a buyer of the value the additional structure brings. Plus, building an ADU adds to your property’s value overall – an investment you’ll reap when it comes time to sell.

10. Ease of navigation for older adults

For older family members and those with mobility challenges, navigating the compact nature of a tiny house may be difficult. Climbing into a loft may not be feasible, while doorways and bathroom entrances (if included in the tiny house) may not be wide enough to accommodate. ADUs in California must be built with ADA accessibility top of mind, with features like wide doorways to accommodate wheelchairs and other mobility devices, among other examples.

Choose ADUs for more versatile living

Exterior of Spacials One Bedroom ADU
Photo by Spacial

Let’s say you want to build housing for an aging grandparent, generate rental income from your property, or create a separate working space next to your house. A versatile, well-designed ADU can be just the right solution for these goals and your family’s needs. So when it comes time to design and build your ADU, don’t go it alone: Partner with the experts at Spacial for a modular, fully-managed ADU construction process.

While it may not be a tiny house by definition, the right ADU can scratch the itch for minimalist living. Spacial’s beautifully-designed modern homes feel light, airy, and open without adding extra square footage you don’t want or need. 

With Spacial, modular designs cut out the need for architects and designers while simplifying the material sourcing process, cutting wait times and delays from the get-go. The whole ADU is constructed off-site, resulting in minimal disruptions to your daily life. Best of all, the experts at Spacial handle the whole process from start to finish. All you need to do is sit back and relax while we handle permitting and other vital documentation on your behalf. Reach out to Spacial now to learn more about our process.