Detached ADU Height: Why 16 Feet Isn't Always the Limit

You've got the backyard and the plan: a detached ADU with enough ceiling to feel like a real home — maybe a unit over a garage, maybe a roofline that matches the house. Then you open your city's code and hit the wall: “detached units: One story, 16 ft. maximum.” One line, and your design gets flattened to a single story.

Here's the thing: for a lot of projects, that flat 16-foot cap is more restrictive than what state law requires — and HCD has been telling cities exactly that.

The height floors state law sets

California's ADU statute doesn't set one height number. Government Code § 66321(b)(4) bars a city from imposing a height limit below a set of floors that depend on the situation:

• 16 feet for a detached ADU on a lot with an existing or proposed single-family or multifamily dwelling.
• 18 feet for that detached ADU if it's within one-half mile walking distance of a major transit stop or a high-quality transit corridor — plus an additional two feet to accommodate a roof pitch aligned with the primary dwelling.
• 18 feet for a detached ADU on a lot with an existing or proposed multifamily, multistory dwelling.
• 25 feet, or the primary dwelling's zoning height limit if that's lower, for an ADU attached to the primary dwelling.

So 16 feet is the floor only for the plain-vanilla case. Put the same detached ADU near transit or on a multistory multifamily lot, and the floor rises to 18 feet. Attach it, and the number can reach 25 feet. A code that stops everyone at “16 ft, one story” quietly erases the taller allowances the statute sets.

Calabasas: “One story, 16 ft. maximum”

Reviewing Calabasas's ADU ordinance, HCD went straight to the height table. The table listed, for “detached units: One story, 16 ft. maximum.” HCD's response was direct: “State ADU Law prohibits a height limitation that is more restrictive than any of the following for detached ADUs” — and then it laid out the 16-, 18-, 18-, and 25-foot allowances word for word, and told the city it “must amend the Ordinance to include all omitted missing height allowances.”

The problem wasn't the number 16 by itself. It was the “one story” ceiling and the missing 18- and 25-foot cases — the allowances that apply near transit, on multistory multifamily lots, and for attached units.

Verified against HCD's ADU Ordinance Findings letter to the City of Calabasas, dated May 4, 2026 (Finding 11, Section 17.11.170 Development Requirements Table – Height limit).

Same cap, different cities

Calabasas isn't alone. HCD has flagged the same height problem in ordinance after ordinance.

• Moreno Valley set “a height limit of 16 feet for detached ADUs with multifamily primary dwellings.” HCD pointed to § 66321, subdivision (b)(4)(B) and (b)(4)(C) — which require allowing 18 feet near transit and 18 feet on a lot with a multifamily, multistory dwelling — and told the city to “amend the Ordinance to reflect lawful height limits.”
• Compton's ordinance said certain units “shall not exceed a height limit of 16 feet.” HCD noted the statute “increases height maximums under certain conditions” and told the city to “amend the ordinance to allow the height maximums provided in Government Code section 66321 (b)(4).”
• West Sacramento tied ADU height to what the “underlying zoning district” allowed instead of the state floors. HCD said the city must “apply, at a minimum, the height limits required under State ADU Law” in § 66321, subdivision (b)(4).

Different wording, one pattern HCD keeps catching: a local rule that holds a detached ADU below the 18- or 25-foot floor state law sets for the situation.

What it means for your project

If your city is holding your detached ADU to 16 feet or “one story” — and your lot sits near a major transit stop, carries a multistory multifamily building, or you're attaching the unit — the taller floor may be yours by statute, not by variance.

Two cautions before you rely on it. First, these are HCD enforcement letters — HCD's interpretation of the law, not a court ruling; a city can adopt findings and push back. Second, which floor applies turns on your lot's specifics: transit distance, dwelling type, attached versus detached. So confirm the details with your building department or a land-use attorney before you redraw plans — this isn't legal advice. But the floors are written into statewide statute, and the “16 ft, one story” line in your local code may not hold against your project.

What CrossBeam does with it

When the letter lands on your desk, CrossBeam turns it around the same day: what each item is actually asking, the code or law behind it, and a written response you can hand to your team or your attorney — the back-and-forth that used to eat weeks, done in a couple of hours.