Automatic Flush Bolt: The Specification Guide for Fire and Non-Fire Paired Door Assemblies

The automatic flush bolt is the positive-latching mechanism on the inactive leaf of a pair of doors that projects into the head and floor strikes automatically every time the active leaf closes, and retracts automatically every time the active leaf opens - without any manual operation from the user. On most fire-rated paired door assemblies, this automatic action is not optional. NFPA 80, the governing standard for fire door installation and inspection, requires positive latching on fire door pairs. On corridor doors in healthcare facilities, NFPA 101 Section 18.3.6.3.8 goes further, specifically mandating automatic flush bolts regardless of what the AHJ might permit under NFPA 80. This guide covers every type, every code requirement, and exactly what to confirm before placing an order.

How the Mechanism Works - and Why the Trigger Detail Matters for Specification

Every automatic flush bolt operates through a trigger mechanism built into each bolt body - one at the top of the inactive leaf engaging the head strike, one at the bottom engaging the floor strike. When the active leaf swings open, its edge contacts the trigger on each bolt, mechanically retracting the bolts and freeing the inactive leaf. When the active leaf closes, the triggers disengage and the bolts spring back into their engaged positions in the head and floor strikes.

This trigger-based operation is what distinguishes automatic flush bolts from their two alternatives:

Manual flush bolts use a thumb slide that a person must push before the inactive leaf can open. They are not automatic in any sense. NFPA 80 Section 6.4.4.5.1 permits manual flush bolts on fire door pairs only where acceptable to the Authority Having Jurisdiction, and only in rooms not normally occupied by humans - transformer vaults and storage rooms are the examples cited in NFPA 80's Annex A. They cannot be used in egress paths, in occupied rooms, or anywhere NFPA 101 governs the occupancy.

Constant latching flush bolts use an automatic bottom bolt and a spring-loaded top bolt that must be manually retracted to open the inactive leaf. The bottom engages automatically like a standard automatic flush bolt; the top requires manual operation. They provide greater security than a standard automatic bolt because the top is under spring tension and cannot be accidentally left unlatched, but they require a deliberate manual action to open the door.

Standard automatic flush bolts - where both top and bottom bolts engage and retract through the active leaf's trigger mechanism - are the correct specification for most paired door applications in occupied spaces.

The NFPA 80 and NFPA 101 Code Distinction Specifiers Must Know

Most hardware schedules treat NFPA 80 as the only applicable fire door standard. For automatic flush bolt specification, this is the most common compliance error made.

NFPA 80 Section 6.4.4.5.1 permits manually operated flush bolts on fire door pairs "where acceptable to the AHJ, provided they do not pose a hazard to safety to life." Annex A limits this exception to rooms not normally occupied by humans. This means a storage room or mechanical equipment room on a fire-rated wall may use manual flush bolts if the AHJ approves.

NFPA 101 Section 18.3.6.3.8 removes that option in healthcare occupancies. It states directly: "Corridor doors utilizing an inactive leaf shall have automatic flush bolts on the inactive leaf to provide positive latching." There is no AHJ exception. A pair of fire-rated corridor doors in a hospital or healthcare facility must have automatic flush bolts - period. This requirement does not apply to a mechanical room in a school, but does apply to any corridor door in a new healthcare occupancy required to comply with NFPA 101.

The practical decision tree for specifiers:

• Is the building a healthcare facility governed by NFPA 101? Automatic flush bolts are mandatory on all corridor door pairs.

• Is the door pair in an occupied room or an egress path in any occupancy? Automatic flush bolts are required.

• Is the door pair serving a storage room, transformer vault, or equipment room not normally occupied, on a fire-rated wall? Manual flush bolts may be acceptable with AHJ approval.

Additionally, NFPA 80 Section 5.2.4.2 Item 7 specifically includes coordinator function in the annual fire door inspection criteria: "If a coordinator is installed, the inactive leaf closes before the active leaf." If the coordinator fails this test during inspection, the fire door assembly fails regardless of the flush bolt type.

Metal Door vs Wood Door: Non-Interchangeable Products

The mortise depth, trigger geometry, and strike interface differ between metal and wood door flush bolts. They are not field-adaptable. Ordering the wrong version means the bolt body does not seat correctly in the door edge and the trigger does not align with the active leaf.

Metal door automatic flush bolts are designed for hollow metal door construction. The Ives FB31P provides matched top and bottom bolts for a paired metal door assembly. The Ives FB31T covers top bolt only where the bottom position is handled separately. The Ives FB32 adds an auxiliary fire latch - a thermally activated secondary latch that engages at elevated temperatures during a fire event, providing additional edge sealing independent of the primary bolt mechanism.

Wood door automatic flush bolts use deeper body dimensions for solid core and composite wood construction. The Ives FB41P covers top and bottom for wood door pairs. The Ives FB41T is top bolt only. The Ives FB42 adds the auxiliary fire latch for fire-rated wood door assemblies. Cal-Royal and PDQ offer metal and wood door variants as well, available through the full automatic flush bolts section.

The auxiliary fire latch - sometimes called an auxiliary fire pin - is only required when the specific tested fire door assembly listing calls for it. Specifying it on an assembly that was not listed with the auxiliary latch does not improve the fire rating. Confirm the door manufacturer's UL 10C listing before adding the fire latch variant to the schedule.

The Coordinator Requirement: Sizing and Why It Cannot Be Skipped

When both leaves of a paired door are fitted with closers, a door coordinator mounted on the frame header controls the closing sequence. Without it, the active leaf can close first and physically block the inactive leaf's trigger from re-engaging the bolts, leaving the inactive leaf unlatched. On a fire door, an unlatched inactive leaf fails both the function and the NFPA 80 annual inspection.

There are two coordinator types. Bar coordinators are surface-mounted to the underside of the frame head. Gravity coordinators mount on the face of the frame. Both control the same function - inactive leaf closes first - through different mechanical engagement methods.

The Ives COR series sizes by door pair width:

Size the coordinator to the actual pair width on the schedule. A coordinator that is too short for the door pair will not control the closing sequence correctly.

If the door manufacturer can supply a listed pair with an open-back strike that eliminates the need for an astragal, a coordinator may not be required. This depends entirely on the specific door and lock configuration and must be confirmed against the tested assembly listing - not assumed.

Why American Locksets for Flush Bolt Projects

An automatic flush bolt specification does not ship alone. It goes alongside the coordinator sized to the pair width, the dust proof floor strike, the head strike, closers on both leaves, and the active leaf hardware. Sourcing all of it from a single authorized dealer on one order eliminates the scheduling risk of components arriving separately and the coordination overhead of managing multiple suppliers.

American Locksets stocks the complete Ives, Cal-Royal, PDQ, and Rockwood automatic flush bolt lines from authorized distribution - metal and wood door versions, top bolt only and top-and-bottom sets, standard and fire latch variants, and the full Ives COR coordinator series in all standard sizes. For the complete paired door hardware package, the bolts and latches section covers every flush bolt configuration alongside related hardware, and builders hardware carries coordinators, door stops, and architectural trim. Same-day shipping from multiple US warehouses. 

Call 877-471-4870 with the door pair width, door material, fire rating, and occupancy type. We confirm the correct flush bolt model, fire latch requirement, and coordinator size before the order ships.

Conclusion

The automatic flush bolt is the positive-latching hardware that keeps the inactive leaf of a paired door assembly properly secured every time the active leaf closes. Under NFPA 80, most fire-rated paired door assemblies require it. Under NFPA 101, healthcare corridor doors require it explicitly with no AHJ exception. Metal and wood door versions are not interchangeable. The coordinator must be sized to the actual pair width and present whenever both leaves carry closers. Add the auxiliary fire latch only when the tested assembly listing specifically requires it. American Locksets carries the complete automatic flush bolt range from Ives, Cal-Royal, PDQ, and Rockwood with same-day shipping. Call 877-471-4870 to confirm the right specification for your project.

Frequently Asked Questions

What is an automatic flush bolt and how does it work?

 A trigger mechanism in each bolt body retracts both top and bottom bolts when the active leaf opens and re-engages them into head and floor strikes when the active leaf closes. No manual action required.

Are automatic flush bolts always required on fire door pairs under NFPA 80?

Not always. NFPA 80 Section 6.4.4.5.1 permits manual flush bolts with AHJ approval on doors to unoccupied rooms like storage rooms. All occupied spaces require automatic bolts.

When does NFPA 101 require automatic flush bolts specifically?

NFPA 101 Section 18.3.6.3.8 mandates automatic flush bolts on corridor doors with inactive leaves in healthcare occupancies. This overrides any NFPA 80 exception that might otherwise apply.

What is a constant latching flush bolt?

Automatic bottom bolt plus spring-loaded top bolt requiring manual retraction to open. Provides higher security than standard automatic bolts because the top cannot be accidentally left unlatched.

Do automatic flush bolts always require a door coordinator?

Yes, when both leaves carry closers. The coordinator controls the closing sequence - inactive leaf first - so the bolt triggers re-engage correctly. Without it, the active leaf can close first and leave the inactive leaf unlatched.

Can I use a metal door automatic flush bolt on a wood door?

No. Body dimensions, trigger geometry, and strike interface differ between metal and wood door versions. They are engineered for different door constructions and are not field-adaptable.

Where can I buy automatic flush bolts from Ives, Cal-Royal, or PDQ?

American Locksets carries the full range at americanlocksets.com/automatic-flush-bolts with same-day shipping. Call 877-471-4870 to confirm the right model and coordinator size.

Published by the American Locksets Hardware Team. Authorized Dealer, Est. 2001, Monroe, NY.