Fire-rated doors: 20-min, 90-min, or 3-hour — what to spec when
UL 10C ratings drive frame, glass, and hardware decisions throughout the opening. Here's how to read the schedule and what each rating actually requires.
Fire ratings on the door schedule aren't suggestions — they're how the architect signals which life-safety code provisions apply. Get the rating wrong and you'll fail inspection. Worse, you'll have to swap the assembly after install.
How fire ratings work
A fire-rated door assembly is tested at an independent lab (UL is the most common) under the UL 10C standard, which subjects the assembly to high heat for a specified duration. The rating describes the duration the assembly will resist fire passage — 20 minutes, 45 minutes, 60 minutes, 90 minutes, or 180 minutes (3 hours).
Importantly, the rating applies to the entire assembly: door, frame, hardware, and any glazing. Replace any component with a non-rated equivalent and the rating is void.
Which rating goes where
- 20-minute: smoke-only openings, corridor walls in business and mercantile occupancies, some 1-hour-rated partition openings.
- 45-minute: 1-hour-rated walls (corridor, separation), most common rating in tenant build-outs.
- 60-minute (1-hour): exit access corridors in healthcare, 1-hour fire barriers.
- 90-minute (1.5-hour): 2-hour fire barriers, occupancy separations, stair enclosures up to 3 stories.
- 180-minute (3-hour): stair enclosures over 3 stories, 4-hour fire walls, area separations.
A door's required rating is usually 3/4 the rating of the wall it's installed in. A 1-hour wall needs a 45-minute door; a 2-hour wall needs a 90-minute door. Always confirm with the architect of record — and never spec down to save money.
What changes with the rating
- Door core: 20-min and 45-min can use hollow metal or mineral-core wood. 90-min and 3-hour are almost always hollow metal or specialized fire-rated wood.
- Frame: knock-down frames are rated up to 90 minutes. Welded frames are required for many 3-hour applications.
- Glass: traditional wired glass is being phased out. Most fire-rated jobs now use ceramic glazing (like FireLite or Pyran) for any lite over 100 sq in.
- Hardware: self-closing devices (closers) are required on all fire-rated doors. Positive-latching locks (auto-latching) are required on most. Hold-open devices must be tied to the fire alarm.
- Gasketing: smoke seals (intumescent strips) are required on most fire-rated assemblies. Check the listing.
The label
Every fire-rated door and frame ships with a permanent metal label on the hinge edge (door) or jamb (frame). The label identifies the testing agency, the rating, and any specific limitations. Inspectors look for it. If the label is missing or painted over, the opening fails. Tell your painters not to cover them.
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