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A UL 10C fire-rated door lock is a mortise lock that has been independently tested and certified to maintain structural and functional integrity under positive-pressure fire conditions, in compliance with ANSI/BHMA A156.13 Grade 1 performance standards. Choosing the right model requires matching the lock's function, physical dimensions, and certification to your specific opening type, door thickness, and building code requirements.
This guide walks through the key selection criteria — lock body function, door thickness compatibility, backset distance, and how D&D Hardware's UL 10C product range addresses each factor.
A UL 10C certified door lock has passed the positive pressure fire test for door assemblies, as defined by Underwriters Laboratories. Unlike older fire test standards, UL 10C simulates real fire conditions where air pressure differentials can cause doors to bow outward — a scenario that places significantly greater stress on the locking mechanism.
For commercial projects in the United States, specifying a UL 10C fire-rated door lock is not optional on fire-rated openings. It is a code-compliance requirement under NFPA 80, the Standard for Fire Doors and Other Opening Protectives. Locks that are not UL 10C listed cannot be installed on positive-pressure-rated fire door assemblies in regulated occupancies.
Key point: UL 10C certification applies to the complete door assembly. The lock must be tested and listed as part of that assembly — not evaluated in isolation.
Yes. For commercial fire-rated openings, the lock body must meet ANSI/BHMA A156.13 Grade 1 — the highest performance grade in the American standard for mortise locks and latches.
ANSI/BHMA A156.13 Grade 1 requires locks to withstand:
250,000 operating cycles (lever or trim)
Grade 1 security and force resistance
Specific latchbolt, deadbolt, and strike performance thresholds
A lock that carries UL 10C listing but does not meet ANSI/BHMA A156.13 Grade 1 may not satisfy project specifications for high-traffic or high-security commercial environments. Always verify both certifications when reviewing product datasheets.
D&D Hardware's UL 10C fire-rated door locks — including the DDAL04, DDAL05, DDAL07, and DDAL20 — are manufactured to ANSI Grade 1 standards and are available in SUS304 stainless steel construction for long-term durability in demanding commercial environments. You can review the full certified door hardware range at danddhardware.com.
The single most important selection decision is matching the lock function to the intended use of the door. The wrong lock function creates either a security gap or a life-safety violation.
A classroom lock — sometimes called a "corridor" or "institutional" function — is locked and unlocked from the outside by key only. The inside lever always allows free egress. This function is required in educational occupancies where lockdown procedures are a life-safety consideration.
Best suited for: K–12 schools, university buildings, training facilities, and any room requiring controlled exterior access with unrestricted interior egress.
D&D's DDAL05 (SS304 ANSI Grade 1 Latchbolt Mortice Lock for Classroom Door) is designed for this application. It supports fire-rated openings and complies with ANSI Grade 1 requirements.
A storeroom lock is always locked from the outside. The inside lever allows free egress at all times, but exterior access requires a key at every entry. There is no holdback position.
Best suited for: Storage rooms, utility closets, server rooms, pharmacies, and any space requiring constant exterior security without the need to toggle between locked and unlocked states.
D&D's DDAL07 (SS304 ANSI Grade 1 American Style Door Lock for Storeroom) is a UL 10C-listed option suited for this function in fire-rated commercial door assemblies.
A passage function has no locking mechanism. Both levers retract the latchbolt freely from either side. It is used where free passage is required at all times but a latching mechanism is needed to keep the door closed.
Best suited for: Corridors, restrooms, mechanical rooms, and other non-secured openings within a fire-rated assembly where security is not required but fire containment is.
An entry lock can be locked or unlocked from the outside using a key or thumb turn, while the inside lever provides free egress. This function is common in private offices, reception areas, and executive suites.
Best suited for: Office doors, consultation rooms, and patient rooms in healthcare facilities — any space requiring intermittent key-controlled access.
D&D's DDAL04 (ANSI Grade 1 Stainless Steel 304 Mortice Entry Door Lock) and DDAL20 (SUS304 ANSI Grade 1 Most Secure Door Lock for Entrance Door) serve this function in fire-rated configurations.
UL 10C fire-rated door locks are engineered for specific door thickness ranges. Installing a lock outside its rated thickness tolerance can compromise the UL listing, void the warranty, and create a non-compliant opening.
Door Type | Typical Thickness Range | Recommended Approach |
|---|---|---|
Standard steel hollow metal door | 1-3/4 in. (44 mm) | Most ANSI mortise locks are factory-set for this thickness |
Heavy-duty steel door | 1-3/4 in. to 2 in. (44–51 mm) | Confirm lock face and case dimensions |
Solid wood fire door | 1-3/4 in. to 2-1/4 in. (44–57 mm) | Verify case depth and prepare mortise pocket accordingly |
Extra-thick or specialty door | 2-1/4 in.+ (57 mm+) | Contact manufacturer for custom or extended-case options |
Selection tip: Always confirm the lock manufacturer's specified door thickness range in the product datasheet before ordering. D&D Hardware provides full dimensional specifications for each lock model and can support custom requirements through its in-house design team. Contact the D&D technical team at sales@danddhardware.com to confirm compatibility.
Backset is the horizontal distance from the edge of the door (the face of the lock) to the center of the keyhole or lever spindle. Selecting the wrong backset means the lock will not align with the door's edge preparation, strike plate, or frame.
The two standard backsets for commercial mortise locks in the United States are:
2-3/4 in. (70 mm): The most common backset for standard commercial doors. Used in the majority of hollow metal and wood fire door applications.
2-3/8 in. (60 mm): Less common in commercial applications; occasionally specified for narrower stile doors or retrofit projects.
How to determine the correct backset:
Check the original hardware schedule or architectural specification for the project.
If replacing an existing lock, measure from the door edge to the center of the existing cylinder hole.
If specifying for new construction, confirm the backset with the door manufacturer before the door is prepared (mortised).
Most D&D ANSI Grade 1 mortise locks ship with a standard 2-3/4 in. (70 mm) backset. Confirm the requirement with your project specification or contact D&D directly for backset options across the product range.
Before placing an order or submitting a hardware schedule, use this checklist to verify your selection is complete and compliant:
Lock carries UL 10C listing (positive pressure fire test)
Lock meets ANSI/BHMA A156.13 Grade 1 standard
Lock function matches the door's intended use (classroom / storeroom / passage / entry)
Lock is compatible with the door thickness specified
Backset matches the door preparation (2-3/4 in. or 2-3/8 in.)
Lock material (e.g., SUS304 stainless steel) suits the project's corrosion and durability requirements
Lock is specified as part of a complete, listed fire door assembly
Lock finish matches the hardware schedule (satin stainless, satin chrome, etc.)
Trim (lever handle, escutcheon) is listed and compatible with the lock body
Q: Can I use any Grade 1 mortise lock on a fire-rated door?
No. The lock must carry a UL 10C listing specifically — not just ANSI/BHMA Grade 1 certification. ANSI Grade 1 measures mechanical performance under normal use conditions. UL 10C verifies performance under fire and positive-pressure conditions. Both certifications are required for fire-rated commercial openings in the U.S.
Q: What is the difference between UL 10B and UL 10C for door locks?
UL 10B covers neutral-pressure fire tests, while UL 10C covers positive-pressure fire tests. Positive-pressure conditions are more demanding and are the current standard required by NFPA 80 for fire door assemblies. UL 10C is the applicable certification for most regulated commercial projects in the United States.
Q: Do I need a different lock for a double fire door opening?
Yes, double door openings typically require coordinated hardware, including an overlapping astragal or automatic flush bolts on the inactive leaf, and may require a different lock function on the active leaf. Verify the complete hardware schedule against the door manufacturer's UL-listed assembly requirements for double openings.
Q: How do I verify that a manufacturer's UL 10C listing is current and valid?
You can search the UL Product iQ database (iq.ul.com) using the manufacturer's name or product model to confirm the listing is active. Always request a copy of the UL certificate from the supplier and cross-reference the listed product models against what is being quoted for your project.
Q: Where can I source UL 10C fire-rated door locks with ANSI Grade 1 certification?
D&D Hardware Industrial Co., Ltd. manufactures a range of UL 10C listed, ANSI Grade 1 fire-rated mortise locks for commercial applications. With over 18 years of manufacturing experience and an SGS-audited factory, D&D supplies certified fire door hardware to projects across North America, Europe, and the Middle East. View the full door lock range or submit a project inquiry at danddhardware.com.
