Fire Ratings & Smart Locks: The UL 10C Guide

Executive Summary

If you live in a condo, apartment complex, or have a door leading to an attached garage, your door is likely a Rated Fire Assembly.

Drilling a hole in this door to install a smart lock can:

1. Void the Fire Rating (Illegal).
2. Violate Insurance Policies (No payout if house burns).
3. Endanger Lives (Smoke spreads in minutes).

This guide explains UL 10C, the modern standard for fire door safety, and how to stay compliant.

What is UL 10C? (The "Positive Pressure" Test)

Old standards (UL 10B) tested doors with "Neutral Pressure." UL 10C is the harder "Positive Pressure" test.

• The Scenario: In a real fire, superheated air expands, creating high pressure that pushes smoke out through the gaps in the door.
• The Test: The door is put in a furnace at 1900°F (1000°C). Air pressure is pumped inside to try and force flames through the lock hole and under the door.
• The Hose Stream: Immediately after baking, the door is blasted with a high-pressure fire hose. If the glass breaks or the lock falls off, it fails.

Retrofitting: The "Modification" Trap

The Golden Rule: You cannot modify a fire door in the field without recertification.

Allowed Modifications (Usually Safe)

• Swapping Hardware: Replacing an existing specific cylindrical lock with a UL Listed smart lock that fits the exact same hole pattern.
• Drilling Mounting Holes: Limited. You are often allowed to drill small holes (e.g., for thru-bolts) if the lock manufacturer's instructions specifically say it is allowed for fire doors.

Prohibited Modifications (Destructive)

• Boring New Holes: You cannot drill a new 2-1/8" bore hole. This destroys the inner core integrity.
• Chumming / Mortising: You cannot chisel out wood to fit a larger faceplate.
• Removing Latches: You cannot remove a generic latch and replace it with a non-fire-rated motorized latch.

The "Label" Rule

Every fire door has a metal or adhesive label on the hinge edge. NEVER PAINT OVER THIS LABEL. If a fire inspector cannot read the label, they will fail the entire building inspection.

Smart Lock Certification Checklist

Before buying a smart lock for a garage or condo door:

1. Check for "UL 10C" or "UL 10B" Listing:

   • Look for the specific "UL" logo on the box.
   • Note: Some locks are "Grade 1" (Strong) but NOT "Fire Rated" (Heat resistant). Do not confuse them.
   • Schlage / Yale / Kwikset: Most of their pro lines are 20-minute fire rated.
   • Cheap Imports: Often have zero fire rating. The melted plastic keypad can drip into the latch mechanism and fuse the door shut, trapping you inside.

2. The 20 vs 90 Minute Rating:

   • 20 Minute: Standard for residential garage doors. Most smart locks pass this.
   • 90 Minute: Required for stairwells in high-rises. Requires simpler, specialized hardware.

The "Negative Pressure" Myth

Some older contractors still talk about "Negative Pressure" tests (UL 10B).

• Myth: "The fire sucks the door shut."
• Reality: Modern codes (IBC 2000+) require Positive Pressure walls. The fire pushes out. This is why Intumescent Seals (expandable heat strips) are critical. If your retrofitted lock disturbs the seal, the door fails.

Related Tools

• Installation Cost Estimator: Factor in the cost of a locksmith for fire door certification.
• ANSI/BHMA Grading: Durability standards vs Fire standards.

Frequently Asked Questions

Can I use a Wi-Fi bridge on a fire door?

Yes, the bridge plugs into the wall. It is not part of the door assembly.

My lock melted in a fire. Is that a failure?

Not necessarily. The lock's job in a fire is Latching, not operating. It must keep the door Closed (Latched) to stop fire spread. It is acceptable if the electronics melt, as long as the metal bolt stays extended and keeps the door shut against the hose stream.

Can I install a smart lock on a dedicated Fire Exit?

NO. Fire Exits (Panic Bars) require single-motion egress. A deadbolt requires two motions (unlock, then turn handle). Installing a deadbolt on a designated Fire Exit path is a severe code violation.