What is the maximum glass size allowed in a 60-minute fire-rated door?
The standard maximum is 100 square inches of fire-protective glazing (approximately 10” x 10”). Larger vision lites are possible if fire-resistive glazing is used and the complete assembly (door, frame, glass, and lite kit) is covered by a specific UL or WHI listing that permits the larger size. The listing, not the glass type alone, determines the maximum area.
Can I replace wired glass with ceramic glass in an existing fire-rated door?
Only if the replacement glass, lite kit, and installation method are covered by the same listing as the existing door assembly. You cannot substitute one glass type for another based on general fire ratings. The specific listing must include the ceramic glass product as an approved option for that door and lite kit combination.
What is the difference between fire-protective and fire-resistive glazing?
Fire-protective glazing blocks flames and smoke but allows radiant heat to pass through. Fire-resistive glazing blocks flames, smoke, and radiant heat. Fire-resistive glazing meets wall assembly test criteria (ASTM E119) and can be used in larger sizes at higher fire ratings. Fire-protective glazing is limited to 100 square inches in 60-minute and 90-minute doors.
Is wired glass still allowed in fire-rated doors?
Wired glass is still listed for fire-rated applications, but its use is restricted in locations where safety glazing is required. It does not meet impact safety standards (CPSC 16 CFR 1201 or ANSI Z97.1) on its own. Many code editions and jurisdictions prohibit wired glass in schools, healthcare facilities, and other locations where human impact is likely. Check with the AHJ and current code edition for your project.
Can I field-cut a 90-minute fire-rated door to add a vision lite?
No. UL and WHI listings for 90-minute fire-rated doors require that lite cutouts be factory-prepared. Field-cutting a 90-minute door voids the fire rating. The same prohibition applies to 3-hour rated doors. CDF factory-prepares all lite cutouts in 90-minute and 3-hour rated doors before shipment.
What happens if my fire-rated door has oversized glazing?
The fire rating of the entire assembly is voided. The door will fail inspection, the building loses code compliance, and the assembly must be replaced. An oversized lite cutout cannot be repaired in the field. The door must be replaced with a correctly listed assembly.
Do temperature rise doors require special glazing?
Temperature rise doors can use standard fire-protective glazing at 100 square inches or less. For larger glass areas, fire-resistive glazing is required because it blocks radiant heat and allows the assembly to meet the 450-degree temperature rise limit at 30 minutes. The specific listing must cover the glass type and size for temperature rise compliance.
Why does the fire rating determine the maximum glass size?
Higher fire ratings require the assembly to withstand longer fire exposure. Glass, even fire-rated glass, is a weaker point in the assembly compared to steel or solid wood. The longer the required fire endurance, the less glass area the assembly can tolerate while still passing the fire test. This is why 20-minute doors allow full lites while 90-minute doors are generally limited to 100 square inches with fire-protective glazing.
