ADU Plans: An Introductory Guide to Buying & Building Your Own

What Is an ADU?

Short for “Accessory Dwelling Unit,” an ADU is a self-contained living space on a single lot that can be located inside, attached to, or detached from a single-family home. They have a small floor plan that can be as tiny as 150 square feet and be as big as 1,000 sqare feet or more (local zoning laws may have limitations on how big a unit you are able to legally host), with areas for living, eating, sleeping, and sanitation. Yes, an ADU can be considered a tiny house, but categorically, ADUs are not tiny homes, because the main purpose of an accessory dwelling unit is to provide additional housing on a single-family lot.

Compact and often modular, ADU's are ideal for homeowners who want a home office, guesthouse, or a secondary dwelling for aging family members while maintaining privacy (and, let’s be honest, sanity). Depending on your town or city’s zoning laws, ADUs are a viable option for generating rental income as a short or long-term rental unit as well. The Airbnb or Vrbo option is especially helpful for generating additional income. Either way, an ADU can and likely will increase your property value.

Amidst the housing shortage and high cost of living, constructing an ADU in the backyard of a primary residence has become a trend in many overcrowded and states throughout the US, and they're generally viewed as a solution that can provide more well-designed and affordable housing. California recently lifted restrictions on ADUs and amended its zoning laws to make it easier for property owners to add secondary units.

No matter the endgame, the size, location, and use of your ADU depends entirely on your jurisdiction’s local laws and building codes. Check your county and city zoning laws or visit the municipal clerk’s office to find out if it’s legal to build an ADU on your property. If your jurisdiction doesn’t have specific laws for ADUs, follow the state regulations for guidance. This process will be tedious and perhaps even frustrating at times, as most counties are slow to adapt. Good luck!

ADU Floor Plans

Like any other floor plan, an ADU floor plan, or “plan,” is a scale diagram of a house or property as looked at from a bird’s eye view that shows the layout of a space, including rooms, traffic patterns, and other key features of the home like plumbing, wiring, materials, and other specs. The detailed house plans essentially tell a builder and contractor everything they need to know to build that specific structure from the ground up.

Purchasing a pre-designed floor plan for an ADU project can save time and money that would be spent working with an architect to create custom plans, and the cost upfront (before materials, permits, and hiring experienced building and design professionals to outsource labor) is relatively cheap. The folks at DEN, for example, offer beautifully-designed plans that start at $199. Due to their increasing popularity, the architectural design of ADUs come in a variety of shapes, sizes, and styles with a floor plan to match that are conveniently available to buy online and download in a matter of minutes. Luckily for urbanites, some major cities on the west and east coasts—like Seattle, San Jose, Los Angeles, San Francisco, and Washington D.C.—have pre-approved ADU plans that have been reviewed for compliance with local codes to make the permit process as smooth as possible for hopeful homeowners.

What to Expect When Purchasing ADU Floor Plans

Whether it’s a compact one-bedroom design or a large two-story home, every set of plans will come with standard information that details the build for your contractor, structural engineer, or other building professional. Here’s what to expect in a floor plan set:

• Cover sheet
• Foundation plan
• Floor plans
• Interior elevations
• Exterior elevations
• Roof plan
• Wall details
• Structural plan

It’s highly likely you won’t fully understand the terms, jargon, and symbols in your ADU building plans, and that’s ok. However, before buying, do your best to familiarize yourself with the information by working with a professional to interpret it so you know what you’re getting into when it comes time to contact the local building department to begin permit applications and the creation a site plan.

Unless this is your area of expertise, don’t forgo hiring professionals to complete the build and support you in the process, but do remember that it's your responsibility to prep the site and establish a foundation, find a general contractor, obtain building permits, and even hire a designer or architect if you want to customize the floor plans to suit your needs.

How to Choose the Right ADU Plan

Finding the right ADU design for your property starts with understanding what’s possible, and of course, legal. Don’t think of it so much as a buzzkill, but an opportunity to get creative with all the possibilities laying in wait just outside your door. Who’s to say you won’t be able to build the detached ADU craftsman guest suite of your dreams, or construct a modern multi-family unit with glossy countertops and floor-to-ceiling windows? The ADU that’s right for you meets your use, budget, and style choices, all while being compliant with local building codes. A perfect match. To save you the research, here are a few ADU plans to start with.

Where to Buy ADU Plans

DEN

With over 30 different designs to choose from, DEN’s architect-grade plans equip you to build a design-driven ADU inspired by modern outdoor architecture. Aside from their great prices (did we mention their high-quality plans start at $199?), they provide budgeting guidance, support for sourcing materials and contractors, and tips for a smooth build process all the way through.

LEARN MORE

Inspired ADUs

The California-based design company creates pre-designed high-end backyard homes that can be built as is or customized with the help of a designer. They also offer a series of modular units, called “Modular Millie,” that are built off-site and arrive as a turnkey home, if prefab is more your style.

LEARN MORE

Cottage

If you’re looking for a full-service design experience with a variety of options and live in San Diego, Los Angeles, or the San Francisco Bay Area, Cottage has 20 different pre-designed ADU floor plans to choose from, or the opportunity to begin carte blanche and co-create your dream ADU. Once you’ve selected a plan, they’ll work with you every step of the way to secure ADU permits, hire vetted builders, and construct your new backyard home.

LEARN MORE

Elevated Spaces

Based in California, Jeff Waldman and partner Molly Fiffer got their start in the ADU game by building their own cabins and a handful of other outbuildings on a property in the Santa Cruz mountains. They now sell the plans to these structures under the Elevated Spaces name. Their popular Redwood Cabin package comes with PDF blueprints, a materials list, a cut list, notes on materials and build tips, a digital album of 600 photos and videos of the build process, and a bonus 3D Sketchup model of the cabin—all for $89.

LEARN MORE

Modern ADU Plans

From a modern Japandi design that emphasizes indoor-outdoor living to a more traditional gabled farmhouse clad in cedar shingles, Modern ADU Plans offers a wide range of architectural styles with a slightly higher price tag (most plans cost $995). For $32k, Modern ADU Plans will work with you to custom design a sustainable secondary dwelling at a fixed price.

LEARN MORE