Aliso Viejo's ADU Window Rule: HCD Calls It a Hidden Setback

You've drawn the ADU. Then the plan checker stops on the windows: the ones facing your neighbor can't stay. The rule says an ADU's windows and doors "may not have a direct line of sight to an adjoining residential property" — screen them with fencing or privacy glass, or move them. It sounds like a reasonable privacy courtesy. HCD's read is that it's something else entirely: a setback in disguise.

Here's the thing: a rule about where your windows can face can quietly function as a rule about where your building can sit — and State ADU Law is strict about how far a city can push an ADU off the property line.

What Aliso Viejo's ordinance said

Aliso Viejo adopted ADU Ordinance No. 2023-235 on March 1, 2023. Its window rule, at Municipal Code § 15.14.080(I)(7)(a), reads:

"Windows and doors of the accessory dwelling unit may not have a direct line of sight to an adjoining residential property. Fencing or privacy glass may be used to provide screening and prevent a direct line of sight."

On paper it governs glass. In practice, if you can't put a window on the wall that faces your neighbor, you either wrap that wall in screening or pull the building back until the sightline clears — which is another way of saying "stand farther from the lot line."

What HCD found

HCD reviewed the ordinance and, in an Ordinance Findings Letter dated June 25, 2024, took direct aim at the window rule. Its language was blunt:

"Line-of-sight requirements constitute implicit setback requirements inconsistent with State ADU Law and could be considered arbitrary, excessive, or burdensome."

HCD's finding went further on feasibility: "Placement of windows and doors is regulated by building and fire codes. Applying additional placement requirements based on line-of-sight may conflict with safety codes and render ADU construction infeasible." HCD also noted the ordinance never defines "direct line of sight," "adjoining residential property," or "fencing or privacy glass," which — in HCD's view — leaves room for discretionary judgment on a supposedly ministerial permit.

Verified against HCD's Accessory Dwelling Unit Ordinance Findings letter to the City of Aliso Viejo, dated June 25, 2024 (Finding 13, Ordinance No. 2023-235, § 15.14.080(I)(7)(a)).

Why a sightline rule reads as a setback

The math is in the statute HCD cited. Under Government Code § 66314(d)(7), a city can require "a setback of no more than four feet from the side and rear lot lines" for a new ADU — and no setback at all for one converted from, or rebuilt in the footprint of, an existing structure. Four feet is the ceiling.

A "no line of sight" rule can blow past that ceiling without ever using the word "setback." If honoring the neighbor's sightline forces your wall — windows and all — farther from the property line than four feet, the city has, in HCD's reading, imposed a setback state law doesn't permit. HCD's conclusion on this finding: the city "must either remove this requirement or amend the Ordinance to comply with State ADU Laws' objective standards and ministerial review provisions."

One finding out of twenty

The window rule wasn't the only design standard HCD flagged. The letter lists 20 numbered findings against the ordinance — from deed restrictions and owner-occupancy language to lighting, tree replacement, and interior-dimension minimums. A second window rule drew fire too: § 15.14.080(I)(7)(g) required windows and doors within 30 feet of a property line (other than a public right-of-way) to be clerestory windows or "frosted or obscured glass." HCD found that one undefined and, in effect, a de facto size requirement — noting it could conflict with egress safety codes.

The through-line across HCD's findings is a single test: on a ministerial ADU permit, standards have to be objective — measurable against a fixed benchmark, "knowable" before you apply — not a call a reviewer makes by eye.

What this means for your project

If a reviewer is holding up your ADU because a window "faces" a neighbor, that's the kind of requirement HCD has said reads as an implicit setback and a subjective standard rolled into one. That's worth knowing before you redraw the elevations.

Two cautions, though. An HCD findings letter is HCD's interpretation of State ADU Law, not a court ruling — courts have the final word, and a city can also respond by adopting findings that defend its ordinance rather than amending it. Aliso Viejo had 30 days to respond, by July 24, 2024, or risk referral to the Attorney General. So confirm your city's current ADU ordinance and run your specific situation past your local planning department or an attorney. Treat this as background, not legal advice.

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.