Stucco on the California coast: which counties now owe a rainscreen

If you stucco houses in San Diego, San Francisco, or Humboldt County, the 2025 Residential Code now spells it out by county: plain two-layer paper behind the lath isn't enough — you owe a drainage space too.

Here's the thing: the errata didn't invent that requirement. The code already splits stucco water-resistive-barrier rules into two tiers — a dry-climate rule in R703.7.3.1 and a moist-or-marine rule in R703.7.3.2 that adds drainage on top of it. What the January 2026 errata changed is how the code tells you which tier you're in. And it finally answers that by county.

What the errata actually changed

The old text sorted the two rules with weather-classification labels. R703.7.3.1 was keyed to "Dry (B)"; R703.7.3.2 to "the Moist (A) or Marine (C)." Those are Köppen-style climate terms — not anything stamped on a permit or a site address.

The errata struck them. R703.7.3.1 now applies in "other than IECC 3 (marine) and 4 (marine)" climate zones; R703.7.3.2 applies in "IECC 3 (marine) and 4 (marine)" zones. Both send you to one lookup — Table R702.7.3 — to find your zone. The same correction also deleted a stale cross-reference to Section R702.7.3 from the subsection text.

Verified against the corrected text of CRC R703.7.3.1 and R703.7.3.2 and the change wording in BSC Information Bulletin 26-01, effective January 1, 2026.

The county list that decides it

Here's why the swap is useful: in this table, IECC climate zones follow county political boundary lines — whole counties, no metes-and-bounds guesswork. Table R702.7.3 names them.

IECC 3 (marine) covers Mendocino, Sonoma, Marin, San Francisco, San Mateo, Alameda, Santa Cruz, Monterey, San Benito, San Luis Obispo, Santa Barbara, Ventura, and San Diego counties. IECC 4 (marine) covers Del Norte and Humboldt. A stucco job in any of those counties is in R703.7.3.2 territory.

Verified against Table R702.7.3 (IECC vs. California Energy Code Climate Zone Comparison), 2025 CRC Chapter 7.

One catch worth flagging: not every coastal county sits in a "marine" row. The table puts Los Angeles and Orange counties in plain IECC 3 — not 3 (marine) — so per the table, stucco there falls under the dry-climate rule, R703.7.3.1. And watch Ventura County: the table lists it in both rows — plain IECC 3 and 3 (marine) — so for a Ventura job, confirm the governing zone with the building department rather than assuming. "Coastal" isn't the test; the county's zone assignment is. Read the row, don't eyeball the map.

Inland vs. coastal: what each tier asks for

In the non-marine zones (R703.7.3.1), the barrier behind stucco has to be one of two things: two layers of 10-minute Grade D paper (or a barrier with water resistance equal to or greater than two layers of ASTM E2556, Type I), or one layer of 60-minute Grade D paper (or ASTM E2556, Type II) separated from the stucco by foam plastic insulating sheathing, another non-water-absorbing layer, or a drainage means.

In the marine zones (R703.7.3.2), you do that and add drainage. Two paths:

• A space or drainage material not less than 3/16 inch (5 mm) in depth on the exterior side of the water-resistive barrier — a rainscreen gap, on top of the R703.7.3.1 assembly.
• Or, building on the 60-minute-paper option, drainage with a drainage efficiency of not less than 90 percent, measured in accordance with ASTM E2273 or Annex A2 of ASTM E2925.

Verified against CRC R703.7.3.2, Items 1 and 2, 2025 edition with January 2026 errata.

So the binary is clean. Inland: two-layer paper does the job. On the marine coast: that barrier plus either a 3/16-inch drainage space or a 90-percent-efficient drainage layer. On a full-house stucco scope that's a real cost and sequencing difference — which is exactly why a county-level trigger beats a climate label at plan check.

One more table note: the same errata added California Energy Code Zone 7 to the IECC 3 (marine) row of Table R702.7.3.

None of this is new law, and local jurisdictions can adopt stricter requirements — so confirm your county's zone and any local amendments with the building department before you bid the wall. But the statewide baseline now reads in plain zones and county names instead of climate jargon.

What CrossBeam does with it

CrossBeam checks a stucco assembly against the county the job is actually in, and flags when a marine-county wall is missing the 3/16-inch drainage space or 90-percent-efficient drainage layer that R703.7.3.2 requires. It's the kind of inland-versus-coastal call that's easy to miss when the only thing that moved was the words the code uses for your climate.