Every opening the WUI Code polices: windows, doors, and garage gaps

Embers don't knock — they find the gaps

A wildfire rarely burns a house down by pushing a wall of flame through it. It sends embers ahead — sometimes miles ahead — and those embers hunt for a way in. Every window, every door, every skylight, and every crack around a garage door is a candidate opening. That's why California's Wildland-Urban Interface Code (Part 7) doesn't stop at walls and roofs. It writes a rule for each opening.

The code applies to new buildings — and the structures accessory to them — in a State Responsibility Area or a High or Very High Fire Hazard Severity Zone (Section 101.3.1). If your project sits in one of those, two sections govern the windows, doors, and skylights: 504.8 for glazing and 504.9 for doors. (Vents get their own section, 504.10.) Here's the per-opening checklist.

Windows, glazed doors, and skylights (504.8)

Exterior windows, window walls, glazed doors, windows within exterior doors, and skylights each have to meet one of four options:

1. Multilayered glazed panels with at least one pane of tempered glass complying with Section 2406 of the California Building Code.
2. Glass block.
3. 20-minute fire-rated glazing tested to NFPA 257 or UL 9 (and exempt from the hose-stream test).
4. Glazing that meets the performance requirements of SFM Standard 12-7A-2.

For most houses, option 1 is the one you'll spec: a dual-pane unit with a tempered layer. Note the word multilayered — a single pane of tempered glass on its own doesn't satisfy the section.

Then the skylight trap: an operable skylight needs more. Under 504.8.2, it must be protected by a noncombustible mesh screen with openings no larger than 1/8 inch.

Verified against WUI Code §504.8.2: an operable skylight "shall be protected by a noncombustible mesh screen and the dimensions of the openings in the screen shall not exceed 1/8 inch (3.2 mm)."

Exterior doors (504.9)

Exterior doors get six ways to comply:

1. Noncombustible construction.
2. Solid-core wood not less than 1-3/4 inches (44 mm) thick.
3. Solid-core wood built to set dimensions — stiles and rails at least 1-3/8 inches thick, raised panels at least 1-1/4 inches, tapering to a tongue no thinner than 3/8 inch at the panel edge.
4. A 20-minute fire-protection rating tested to NFPA 252, UL 10B, or UL 10C.
5. Exterior surface or cladding that passes ASTM E2707 (under the conditions in 504.9.3).
6. Exterior surface or cladding that meets SFM Standard 12-7A-1.

And any glass in a door — a lite, a glazed panel, a fully glazed door — kicks back to the glazing rules in 504.8. Don't let a decorative window undo a compliant door.

The two rules builders never see coming

Here's the thing: most people spec the door and figure they're done. The WUI Code has two more requirements for the garage — and they're the ones that trip up otherwise-clean plans.

504.9.1 — battery backup. An automatic garage-door opener for a vehicle door serving a residential building must have a battery-backup function. The code doesn't spell out why, but the reason is easy to infer: when the power drops in a fire, you still need to get the car out and get gone. A dead opener on a heavy sectional door strands the vehicle.

504.9.2 — the ember gap. The perimeter of an exterior garage door can't leak. Gaps between the door and the opening — at the bottom, sides, and top — must not exceed 1/8 inch. You control that gap with one or more of three methods:

• Weather-stripping made of a material that holds its tensile strength after 2,000 hours of accelerated weathering (tested to ASTM D638 before and after ASTM G155, with no more than a 10 percent difference) and carries a UL 94 flammability rating of V-2 or better;
• Door overlaps onto the jambs and headers; or
• Metal flashing covering the jambs and headers.

Verified against WUI Code §§504.9.1 and 504.9.2: residential vehicle-door openers require battery backup, and door-to-opening gaps at the bottom, sides, and top are capped at 1/8 inch (3.2 mm).

Run it before you order

Openings are cheap to get right on paper and expensive to fix after the glass and doors ship. Before you place the order, walk the list: a glazing option for every window and skylight, a screen on operable skylights, a compliant door assembly, and — the two easy ones to forget — a battery-backup opener and a sealed garage-door perimeter. Where a detail sits close to the line, confirm the assembly and its listings with your local jurisdiction; this is a checklist, not legal advice.

What CrossBeam does with it

CrossBeam reads a set of plans against the WUI Code's opening rules the way a fire plan checker would — flagging a skylight with no screen note, a garage door missing a battery-backup or perimeter-gap detail, or glazing called out as single-pane tempered. You see the exact section behind each flag, so the correction gets made before it becomes a redline.