Hardware
Flush Bolts for Pairs of Doors
By the Div08 Consulting team · Updated
Flush bolts are bolts mortised into the edge of the inactive leaf of a pair of doors. They lock that leaf to the frame head and the floor so the active leaf has something to latch against. They come in three types: manual, automatic and constant latching (also called self-latching). Building codes limit where manual flush bolts can be used on egress doors.
How flush bolts work on a pair
On a pair of doors, the active leaf usually carries the lock or latch. The inactive leaf needs to be held in place so the active leaf can latch to it. A top flush bolt shoots up into the frame head; a bottom flush bolt shoots down into a strike in the floor. Because they sit in the door edge, they are flush with the face and cannot be reached when the pair is closed.
Manual, automatic and constant latching
| Type | How it operates | Where it fits | Watch out for |
|---|---|---|---|
| Manual | User slides the lever to throw or retract the bolt | Inactive leaves that stay closed most of the time, where code allows | Restricted on egress doors |
| Automatic | Bolts throw automatically when the active leaf closes and retract when it opens | Fire-rated pairs, egress pairs where allowed | Requires a coordinator so the inactive leaf closes first |
| Constant latching (self-latching) | Bolts latch automatically when the inactive leaf closes, retracted by hand; available with an auxiliary fire latch | Pairs where the inactive leaf must latch whenever it is closed | Still need the right closing sequence |
Spec tip
if the pair has automatic flush bolts, it almost always needs a door coordinator. Leaving the coordinator out is one of the most common holes in a hardware submittal.
Egress code limits
The International Building Code generally does not allow manual flush bolts on egress doors, because a person should not need to operate two devices to get out. The IBC permits manual flush bolts in limited cases, for example on the inactive leaf in certain occupancies where that leaf is not needed for egress and panic hardware is not required. The exact conditions depend on the code edition and occupancy, so confirm against the adopted code.
- Where panic hardware is required, use exit devices on both leaves or an approved arrangement, not manual flush bolts. See exit devices.
- Automatic and constant latching flush bolts are the usual answer when the inactive leaf must stay latched on an egress or fire-rated pair.
- Local amendments vary. Check the code official's position on pairs early in design.
Flush bolts on fire-rated pairs
Fire-rated pairs must positively latch. Both leaves need to be held closed during a fire so the pair does not push open under pressure. On the inactive leaf this is usually done with automatic or constant latching flush bolts, or with a vertical rod exit device. NFPA 80 does allow manual flush bolts on fire-rated pairs where the AHJ approves, typically for rooms that are not normally occupied, such as storage rooms and transformer vaults. Some listings allow the bottom bolt to be omitted on certain pairs, often called less-bottom-bolt applications, but only when the door's listing permits it.
- Use flush bolts listed for fire doors and for the door type.
- Check the label and listing before deleting the bottom bolt.
- Coordinate with the astragal and coordinator so the pair closes in order.
Strikes, rod length and other details
- Bottom strike: use a dust-proof strike in the floor so the hole does not fill with debris and become a trip hazard.
- Floor conditions: thresholds and floor finishes change where the bottom strike goes. Coordinate with the threshold.
- Top rod length: standard top bolts are sized for typical door heights; tall doors may need extension rods so the lever stays within reach.
- Door edge prep: flush bolts require door edge preparation. Hollow metal and wood doors must be ordered with the prep.
- Wood doors: check the door manufacturer's limits on edge preps for labeled wood doors.
These details are what a submittal review catches before the doors are ordered.
Frequently asked questions
What is the difference between manual and automatic flush bolts?
Manual flush bolts are thrown and retracted by hand. Automatic flush bolts throw when the active leaf closes and retract when it opens, so nobody has to touch them.
Are manual flush bolts allowed on egress doors?
Generally no. The IBC allows them only in limited situations, such as certain occupancies where the inactive leaf is not needed for egress. Check the adopted code edition.
Do automatic flush bolts need a coordinator?
Usually yes. The inactive leaf must close before the active leaf, and the coordinator enforces that order.
Do fire-rated pairs need top and bottom flush bolts?
The inactive leaf must positively latch. That is usually top and bottom bolts, but some listings permit a top bolt only. Follow the door's listing.
General guidance only. Code requirements depend on the edition your jurisdiction has adopted and on the listing of each fire-rated assembly; confirm with the authority having jurisdiction. Published by Div08 Consulting (John Voll, owner).