The ADU sprinkler exemption is now written into the code itself

The errata

The January 2026 errata to the 2025 California Residential Code adds Exception 2 to Section R309.2 (automatic sprinkler systems for one- and two-family dwellings). It exempts an accessory dwelling unit from the sprinkler requirement when all of the following are met:

1. The unit meets the definition of an Accessory Dwelling Unit in the Government Code.
2. The existing primary residence does not have automatic fire sprinklers.
3. The detached ADU does not exceed 1,200 square feet.
4. The ADU is on the same lot as the primary residence.

Verified against the live ICC code text on June 4, 2026 — R309.2 now carries this exception, stamped "with January 2026 Errata."

What it does

Here's the thing: this exemption isn't new law. It has lived in the Government Code (§66314(d)(12)) for years — an ADU never required sprinklers unless the primary residence did. What changed is where you can find it.

Until now, a plan checker reading the Residential Code saw a flat requirement — "an automatic sprinkler system shall be installed in one- and two-family dwellings" — with no hint of the ADU carve-out. To get it right you had to know the statute and cross-reference it. The predictable result was one of the most common ADU correction foot-faults: a letter demanding sprinklers on a detached ADU where the primary home has none.

Now the building code restates the statute in plain sight. Same outcome, far less room to miss it.

What CrossBeam does with it

CrossBeam already reasoned from the controlling authority — the Government Code — so our sprinkler analysis was right before this errata and is right after it. The update we made was small and deliberate: cross-reference the new R309.2 Exception 2 so a reviewer who lands on the building code sees the same answer, and make sure city overlays that amend R309.2 (Colma, for one) don't accidentally re-impose what state law forbids.

That's the whole point of watching errata: a one-line code change can quietly fix — or break — an everyday review.