The guides
12 plain-English guides. Every figure links to the report, statute or handbook it came from.
What an ADU really costs, and where the money goes
California's statewide survey of ADU owners found a median build cost of $150,000. A public pilot in San Diego spent $176,333 on a one-bedroom. Neither number is the one a builder will quote you first. This guide explains why, and what to budget for.
4 min read · 3 sourcesRead the guide
Five real ADU projects, broken down line by line
A public housing agency built five ADUs and published every cost. Here is what they paid for permits, surveys, design and construction.
3 min read · 2 sources
Prefab vs site-built ADUs
Factory-built units can be faster and sometimes cheaper. The savings depend on your lot, your city and what the quote leaves out.
3 min read · 4 sources
How people actually pay for an ADU
Most owners use cash or home equity. Here is how the main loan options work and what lenders will count.
3 min read · 6 sources
ADU rental income and payback
What ADUs actually rent for, how to run the numbers on your own unit, and the rules that limit short-term rentals.
3 min read · 6 sources
JADU, attached or detached
A junior unit inside your house costs a fraction of a backyard cottage. Here is what each type allows and what it gives up.
3 min read · 3 sources
How long ADU permits really take
State deadlines say 60 days in California. Real projects take longer. Here is what to expect and how to keep yours moving.
3 min read · 4 sources
How big and how tall can your ADU be?
The size, height and design rules that shape most ADUs, with the state minimums cities have to allow.
3 min read · 5 sources
Utilities, sewer and power
Connecting an ADU can cost a few thousand dollars or more than the unit. Here is how to find out which before you sign.
3 min read · 3 sources
Setbacks, HOAs and deed restrictions
What your homeowners association can and cannot do, how setbacks work and why you should read your deed before you design.
3 min read · 4 sourcesAlso read: ADU insurance and property tax · ADU rules in California, Oregon, Washington, Texas and Florida · all guides
Browse by type
41 builders, lenders and specialists, each checked against its own website and described in its own words.
Quick facts, sourced
ADUs permitted in California in 2024, up from 1,336 in 2016.
Source: California HCDmedian cost to build an ADU in California's statewide owner survey.
Source: UC Berkeley CCImedian monthly rent for an ADU in the same survey.
Source: UC Berkeley CCIUS single-family properties with ADUs found in listing data.
Source: Freddie MacFree planning tools
Built on the same public sources as the guides. Nothing you enter leaves your browser unless you send it.
Which ADU fits you?
Six quick questions point you toward a JADU, a conversion, an attached or a detached unit.
Take the quiz →Budget estimator
A rough range from real survey numbers, with every default cited and editable.
Estimate a budget →Timeline builder
A printable plan from design to move-in, using the phase lengths a public pilot actually saw.
Plan the timeline →The Backyard Letter
One short email when we publish something new: a guide, a rule change in your state, or a public cost report worth reading. Every item links to its source. Free, unsubscribe any time.
BackyardStack is independent and reader-first. Builders can request a free listing; paid placements, when we have them, are always labeled. Advertising.