This post was published in Doors & Hardware
Flush bolts are used to secure the inactive leaf of a pair of doors, projecting into the frame head and into a floor strike. In this application, the active leaf would typically have a lockset which latches into a strike mounted on the edge of the inactive leaf. Manual flush bolts and surface bolts are projected and retracted manually, and automatic flush bolts are projected when the active leaf closes and depresses a trigger on the edge of the door. When the active leaf is opened, the automatic flush bolt retracts.
Constant-latching flush bolts are a type of automatic flush bolt – the bottom bolt is a regular automatic flush bolt, but the top bolt latches when the inactive leaf closes, and stays latched until it is retracted manually. Automatic and constant-latching flush bolts are also available with a top bolt only, and an auxiliary fire pin which mounts near the bottom of the door edge and projects when a high temperature is reached during a fire.
There are several different code requirements that affect the use of flush bolts and coordinators – code requirements related to egress, fire protection, and accessibility. It’s important to consider all of the requirements that might apply to a particular pair of doors in order to determine which type of flush bolts may be used – manual, automatic, or constant-latching. If a pair of doors is required to have panic hardware, flush bolts may not be allowed
In the International Building Code (IBC), flush bolts are addressed in the section called “Bolt Locks.” There has been some confusion about whether this section is intended to apply to deadbolts, but the IBC Commentary references the inactive leaf of a pair of doors throughout this section, clarifying the intent. This section of the IBC prohibits the use of manually-operated flush bolts or surface bolts on egress doors, but includes 5 exceptions:
- Manual flush bolts or surface bolts may be used on doors in individual dwelling units or sleeping units if the doors are not required for egress.
- For doors serving storage or equipment rooms, manual flush bolts or surface bolts are permitted.
- For a pair of doors serving a business, factory and industrial, or storage occupancy with an occupant load of less than 50 people, manual flush bolts or surface bolts are allowed. This exception does not require the building to have a sprinkler system, but it only applies to the occupancy types listed here.
- For a pair of doors serving a business, factory and industrial, or storage occupancy where the building is equipped throughout with an automatic sprinkler system, manual flush bolts or surface bolts are allowed if the inactive leaf is not needed in order to meet the egress capacity requirements. For example, if the egress capacity of the active leaf is 160 occupants and the occupant load is 100 people, the inactive leaf is not needed for egress and manual flush bolts or surface bolts are acceptable. This applies only to sprinklered buildings of the referenced occupancy types.
- In a Group I-2 occupancy, such as a hospital or nursing home, patient rooms may have self-latching edge- or surface-mounted bolts if the inactive leaf is not needed to meet the egress capacity requirements. Note that this exception does not allow manually-operated bolts but does allow constant-latching automatic flush bolts.
For exceptions 3, 4, and 5, the IBC states that the inactive leaf shall not contain doorknobs, panic bars, or similar operating hardware, as this hardware could give a building occupant the impression that the inactive leaf may be operable. These exceptions were added in the 2009 edition of the IBC.
A common question is whether an inactive leaf that is provided for convenience, aesthetics, or movement of equipment, and not required for egress is allowed to have manually-operated flush bolts. This is left up to interpretation by the Authority Having Jurisdiction (AHJ) so it is difficult to predict what will be acceptable in each situation. Although the IBC Commentary seems to indicate that doors not intended for egress (including the inactive leaf of some pairs) may not be required to comply with the prohibition on manual bolts, the limitations included in items 3 and 4 above seem to indicate otherwise.
NFPA 101 – The Life Safety Code also limits the use of manual flush bolts in a means of egress, when pairs of doors are required in a means of egress. This is typically interpreted to mean that if the inactive leaf of the pair is needed in order to provide the required amount of egress capacity, manual flush bolts can not be used because they don’t meet the criteria listed in NFPA 101. When the inactive leaf is required for egress, NFPA 101 requires one of the following:
- Each leaf of the pair must have a releasing device that allows the doors to be operated independently – without depending on the release of one leaf before the other, or
- If automatic flush bolts are used, the inactive leaf shall not have surface-mounted hardware which would indicate that the door can be used for egress, and unlatching of either door leaf must not require more than one operation.
For pairs of doors that are part of a fire door assembly, additional requirements must be taken into account. One of the cardinal rules of fire doors is that they are required to be positive-latching – there must be an active latchbolt that automatically latches the door when it comes to a close. For pairs of doors this typically means that automatic flush bolts must be used, but NFPA 80 includes a potential exception to this rule. Where allowed by the AHJ, manual flush bolts or manual surface bolts may be used on pairs of fire doors as long as they do not pose a hazard to life safety. Annex A of NFPA 80 further clarifies this provision, limiting the use of manual bolts to rooms not normally occupied by humans, such as transformer vaults and storage rooms. Annex A also suggests that the inactive leaf on such pairs may not be required to have a door closer. Keep in mind that the code requirements that address elevator machine rooms typically require positive-latching hardware, and therefore manual flush bolts would not be allowed on those rooms.
It’s very important to note that NFPA 101 requires corridor doors in health care occupancies to be self-latching, stating, “Corridor doors utilizing an inactive leaf shall have automatic flush bolts on the inactive leaf to provide positive latching.” This means that the NFPA 80 exception for manual flush bolts and surface bolts does not apply to corridor doors in health care facilities that must comply with NFPA 101. For example, a pair of fire doors serving a mechanical room in a school may have manual flush bolts if acceptable to the AHJ, but a pair of fire doors serving a mechanical room in a hospital corridor is required to have automatic flush bolts if the facility is required to comply with NFPA 101.
When automatic flush bolts are used, a coordinator is typically required to ensure that the doors close in the proper sequence. If both leaves of the pair are opened and the active leaf begins to close first, the coordinator will hold the active leaf open slightly, allowing the inactive leaf to close. When the inactive leaf closes completely, it triggers the coordinator to release the active leaf and allow it to close. Coordinators may require accessories such as filler bars and mounting brackets for a complete installation. Another accessory used with flush bolts is a dust-proof strike for the bottom bolt. Although this type of strike is not required by code, it can result in a cleaner installation than the standard flush bolt strike.
Yet another concern, in addition to egress and fire protection, is accessibility. When the inactive leaf of a pair is required to meet the accessibility standards, manual flush bolts should not be used. Manual flush bolts require tight grasping and pinching to operate, and the bolts are not typically mounted within the acceptable range for operable hardware – 34 inches to 48 inches above the floor. For doors on an accessible route, automatic flush bolts or panic hardware would be a better application.
For more information about flush bolts and coordinators, refer to the applicable codes and standards, or consult the AHJ.
1 – Surface bolts are mounted on the face of the door and are operated manually.
2 – Manual flush bolts are mounted on the door edge and are projected and retracted manually using a small lever.
3 – Automatic flush bolts are projected automatically when the active leaf closes, and retracted when the active leaf opens.
4 – Constant-latching flush bolts are a type of automatic flush bolt, with a self-latching top bolt and an automatic bottom bolt.
5 – Automatic flush bolts are also available with an automatic top bolt paired with an auxiliary fire pin which projects when heated to a high temperature.