Tile roofs in fire zones: rewriting the WUI's §504.2.1 airspace rule

The rule that's changing

Clay and concrete tile, metal profile, barrel shapes — anything with a raised profile — leaves an airspace between the covering and the deck. In a fire, that airspace is an on-ramp for embers. The WUI code's answer is §504.2.1, "Roof covering voids," and the State Fire Marshal has proposed a clean rewrite of it.

Here's the thing: this is proposed text, not law yet. It lives in the SFM 04/25 final express terms that went to the Building Standards Commission for its August 25–27, 2026 meeting. All of the roof items — including this one — sit in the GREEN (uncontested) set, with a recorded action of CAC Approve / Agency Accept. So treat it as a strong signal of where the code is headed, not a requirement you can cite today.

From two paths to one deck rule

Today, §504.2.1 gives you two routes for a profiled roof over a combustible deck.

Verified against the current CWUIC §504.2.1 text in the code corpus: Route one (504.2.1.1) is a 72 lb. cap sheet complying with ASTM D3909 — or 1 inch of mineral wool — plus "bird stops ... at the eaves where the profile fits" and "hip and ridge caps ... mudded in." Route two (504.2.1.2) is a listed and labeled underlayment tested as part of a Class A assembly, with an exception for fire-retardant-treated (FRT) sheathing.

The proposed text throws out both and writes one rule. New 504.2.1.1 "Roof deck" says the deck shall be provided with one of the following over the entire roof deck:

1. a cap sheet complying with ASTM D3909 — note the express terms name the standard without the 72 lb figure that's in today's text (check the product standard yourself for what D3909 requires);
2. a roof assembly that passes the ASTM E108 or UL 790 Class C test when tested without the roof covering; or
3. a minimum 1 inch of noncombustible mineral wool board (or other noncombustible material) between covering and deck.

One quirk worth flagging: in the express terms as printed, the Exception comes before the list. Solid FRT sheathing complying with CBC §2303.2 and labeled for exterior use is exempt from the three options — but you'll read that exemption above the numbered choices, not after them.

The practical headline: the old standalone listed-and-labeled Class A underlayment path is gone. If a detail leaned on it, you'll be choosing from the three deck options instead.

"Where the profile fits" is gone

The eave language gets tighter. Proposed 504.2.1.2 "Eaves" reads: openings at the eaves "shall be protected with fireblocking, or noncombustible birdstops, or eave closures to prevent the intrusion of fire or embers."

What's missing matters. The current escape hatch — bird stops "where the profile fits" — is deleted. The proposed rule expects eave openings closed, and gives you three accepted ways to do it.

Ridges and hips move the same direction. New 504.2.1.3 says openings at hip or ridge caps "shall be mortared or otherwise protected with noncombustible material." That's broader than today's "mudded in" — mortar still works, but so does any noncombustible closure.

Valleys get a second option

Valley flashing (504.2.2, also GREEN) keeps its bones: No. 26 galvanized sheet-gauge corrosion-resistant metal over a 36-inch-wide layer running the full length of the valley. What changes is what goes under it. Instead of only a cap sheet, the proposed text lets you use a Class A roofing assembly — an underlayment plus one layer of No. 26 flashing as the covering, tested to ASTM E108 or UL 790 and installed per its listing — as an alternative to the D3909 cap sheet.

What it means for a reroof

This isn't just new-construction trivia. Under 507.1 (GREEN in the same package), replacing a roof covering — or replacing 50 percent or more of it within a 12-month period — pulls the job into 504.2 and 504.2.1. So the deck rule reaches the tile reroof you're pricing this spring, not only ground-up builds.

The Monday-morning move, if this adopts as written: re-check tile and profile details and underlayment submittals against the three deck options, and swap any "bird stops where profile fits" note for a continuous eave closure. None of this is law yet, and it is not legal advice — confirm the current requirement and effective date with your local jurisdiction before you redraw a detail or write a correction.

For the related cleanup that already moved WUI roofing citations, see our post on reroofing in a fire hazard severity zone.

What CrossBeam does with it

CrossBeam flags when a roof detail or underlayment submittal sits in a Fire Hazard Severity Zone and shows which §504.2.1 path it leans on. When proposed text like this firms up, it keeps the current requirement and the coming one straight — so you're checking plans against the rule that actually applies on your permit date.