Accessory Dwelling Unit

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Accessory Dwelling Unit: Definition and meaning

What are accessory dwelling units?

An Accessory dwelling Unit (a.k.a. ADU) is accessory to a primary residence and has complete independent living facilities for one or more persons and has a few variations:

  • Detached: The unit is separated from the primary structure.
  • Attached: The unit is attached to the primary structure.
  • Repurposed (Converted) Existing Space: Space (e.g., master bedroom, attached garage, storage area, or similar use, or an accessory structure) on the lot of the primary residence that is converted into an independent living unit.
  • JADU: A specific type of conversion of existing space that is contained entirely within an existing or proposed single-family residence. This sounds like a standard in-law unit, does not it?
Types of accessory dwelling units - detached, attached, junior.

How big can an accessory dwelling unit be?

Maximum unit size requirements must allow an ADU of at least 850 square feet, or 1,000 square feet for ADUs with more than one bedroom. The conversion of an existing accessory structure or a portion of the existing primary residence to an ADU is not subject to unit size requirements. For example, an existing 3,000 square-foot barn converted to an ADU would not be subject to the local unit size requirements, regardless of whether a local government has an adopted ADU ordinance.

Can minimum and maximum unit sizes be established for ADUs?

A local government may, by ordinance, establish minimum and maximum unit size requirements for both attached and detached ADUs; however, maximum unit size requirements must allow an ADU of at least 850 square feet, or 1,000 square feet for ADUs with more than one bedroom. For local agencies without an ADU ordinance, maximum unit sizes are 1,200 square feet for a new detached ADU and up to 50 percent of the floor area of the existing primary dwelling for an attached ADU (at least 800 square feet).

Can you build an ADU before the main house?

ADUs must be built on lots with existing or proposed housing. A statewide exemption ADU, found in Government Code section 65852, subdivision (e), is an ADU of up to 800 square feet, 16 feet in height, as potentially limited by a local agency, and with four-foot side and rear yard setbacks. State ADU Law requires that no lot coverage, floor area ratio, open space, or minimum lot size will preclude the construction of a statewide exemption ADU. 

What is junior accessory dwelling unit?

A “junior accessory dwelling unit” or JADU is a unit that is no more than 500 square feet in size and contained entirely within a single-family residence. A JADU may include separate sanitation facilities or may share sanitation facilities with the existing structure. 

Should a property have both an ADU and JADU, JADU law requires owner occupancy of either the newly created JADU or the single-family residence. Under this specific circumstance, a lot with an ADU would be subject to owner-occupancy requirements. 

Too busy to figure it all out on your own?

We are here for you

After dozens of consultations and site visits, we can navigate you through an ADU construction process. But first, let us talk and decide what will be a good fit. Why are we suggesting a video call? This will let us share screen and confirm what may be possible (or not) on the spot. We can also share other projects similar to what you are thinking about. This consultation is free.

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Backdoor Revolution book cover

Backdoor Revolution: The Definitive Guide to ADU Development

Accessory Dwelling Units are a form of residential infill housing that are poised to revolutionize housing in the United States. Unlike other urban development trends, this one is being driven by homeowners, not professional developers. Through case studies, expert interviews, firsthand anecdotes, images, and data analysis, Backdoor Revolution reveals the opportunities, challenges, and best practices of ADU development for homeowners, including costs, financing, design, zoning barriers, and regulatory loopholes. With sections written for policymakers and small housing advocates, Backdoor Revolution offers insightful analysis and a succinct prescription for solutions to municipal and institutional barriers for ADU development.

How to build an In-Law Unit in California book cover

How to Build an In-Law Unit in California: Your Essential Guide

This book provides essential information for homeowners in California who are interested in building an accessory dwelling unit (ADU) – better known as an in-law unit. In addition, the book is useful for real estate agents and contractors who have clients who desire an ADU.

The author walks the reader through his experience of building an ADU and explains how to navigate the State of California’s ADU laws. The book includes helpful information on selecting the type of ADU to build, complying with local ADU ordinances, choosing professionals to work on the project, designing an ADU, obtaining financing, and creating a budget.

As an Amazon Associate Home WiP may earn from qualifying purchases.
ADU Floor PLan 500 sq ft is a sweet spot

Is ADU a good investment?

Legally permitted ADU, built well and on a reasonable budget, is a good investment.

Legally permitted means you have applied for a building permit and, after the construction,  had it finaled by the building inspector. Built well – means built with materials of good quality and by an experienced crew. Reasonable budget means that whatever you have spent on the ADU has a chance to get reflected in the property value.

Three homes in place of one

The legislation passed by California in January 2020 made it possible to add more livable space to a current single family home. You might be surprised by the number of options this law has opened for an average homeowner, who has become a real estate developer overnight.

These options include newly constructed detached or attached ADU and conversion of existing space (garage or basement). You are allowed to build up to 1200sf. This is your living space #2. As an additional option, you may convert existing square feet into a Junior Accessory Dwelling Unit. This makes it your living space #3. Spread your family out or rent out.

ADU Floor Plans 500 sq ft

Challenges with financing

The challenge with some new financing solutions  is that the homeowner misses out on the lion share of the income and/or property appreciation. Your financing partner might be offering you  $300/mo income on the ADU, while if you were able to finance it yourself, your net income could be $850/mo. 

ADU size matters

Accessory Dwelling Unit is a small house. It needs utilities and foundation as much as your main house, but has less footprint to spread the costs over. Hence we always encourage you to build max possible.

Trenching for utilties costs the same whether it is for a 200sq ft ADU, 500sq ft ADU or 1200 sq ft ADU. This is the type of fixed cost that makes per square foot costs ridiculously high for smaller ADUs.

What does it mean - well built?

Construction of a house, whether big or small, is a big and serious endeavor and always a considerable investment. If you are thinking of being an owner-builder, and this is your first project, here are our two book recommendations to read first. 

Visual Handbook book cover

The Visual Handbook of Building and Remodeling

Building a home is a complicated, precise, and labor-intensive process. From drawing a design to selecting the site to laying the foundation, building the frame, installing the plumbing, wiring, HVAC, and everything in between, there are countless opportunities for something to go wrong. So how does a homeowner,  builder, or remodeler make sure that their project stays on track every step of the way? Having a copy of The Visual Handbook of Building and Remodeling, 4th Edition on hand is a great place to start.

Pretty Good House book cover

Pretty Good House - a guide to creating better homes

Pretty Good House provides a framework and set of guidelines for building or renovating a high-performance home that focus on its inhabitants and the environment―but keeps in mind that few people have pockets deep enough to achieve a “perfect” solution. The essential idea is for homeowners to work within their financial and practical constraints both to meet their own needs and do as much for the planet as possible.

As an Amazon Associate Home WiP may earn from qualifying purchases.