Installation of flush bolts is a critical aspect of securing double-door systems in commercial and industrial settings. These devices ensure that inactive leaves remain latched and that doors close in the proper sequence, particularly in high-traffic or safety-sensitive environments. This article provides a detailed overview of flush bolt types, installation considerations, and compliance requirements, drawing exclusively from verified information in the provided source material.
Understanding Flush Bolt Types and Functions
Flush bolts are mechanical devices used to secure the inactive leaf of a pair of doors. They are typically embedded into the edge of the door and extend into the frame or floor strike to prevent the door from opening or to ensure proper closure. The source material categorizes flush bolts into several distinct types, each with unique functionality and installation requirements.
Manual Flush Bolts
Manual flush bolts are operated by a small lever or handle located on the edge of the door. These bolts must be manually extended or retracted by the user, making them suitable for low-traffic or non-egress applications. According to the source documentation, manual flush bolts are typically used in individual dwelling units, storage rooms, or for industrial and business occupancies with an occupant load of fewer than 50 people.
However, manual flush bolts are not recommended for accessible routes due to their reliance on grasping and pinching motions, which may not comply with accessibility standards such as ADA. In such cases, automatic or panic hardware is a more appropriate solution.
Automatic Flush Bolts
Automatic flush bolts are designed to engage automatically when the active leaf of a door pair closes. These devices are typically triggered by a mechanical linkage or sensor that detects the movement of the door. When the active leaf closes, the automatic flush bolt extends into the strike to secure the inactive leaf. Conversely, when the active leaf opens, the bolt retracts.
Automatic flush bolts are particularly useful in environments where frequent door usage is expected and where manual operation could pose an inconvenience or a compliance risk. These bolts are also available with a top bolt only, or with an auxiliary fire pin that projects when exposed to high temperatures, providing an additional layer of fire safety.
Constant-Latching Flush Bolts
A variation of the automatic flush bolt, the constant-latching flush bolt features a self-latching mechanism for the top bolt. Once the inactive leaf closes, the top bolt latches and remains engaged until manually retracted. This design ensures that the inactive leaf remains securely in place even if the active leaf is opened or moved. The source material indicates that constant-latching flush bolts are available with both top and bottom bolts or with a top bolt only.
Surface Bolts
Unlike flush bolts, surface bolts are mounted on the face of the door rather than its edge. These devices are manually operated and are often used in conjunction with other locking mechanisms. Surface bolts are typically found in low-security or non-egress applications and are not commonly used in accessible routes.
Installation Requirements and Accessories
Proper installation of flush bolts is essential for ensuring their functionality and compliance with building codes. The source material highlights several key components and accessories that must be considered during the installation process.
Coordinator Devices
For double-door systems, the use of a coordinator is often necessary to ensure that doors close in the correct sequence. A coordinator is a mechanical device that holds the active leaf slightly open while the inactive leaf closes. Once the inactive leaf is fully closed, the coordinator releases the active leaf to allow it to close as well.
In some cases, coordinators may require additional accessories such as filler bars or mounting brackets to complete the installation. These components help to align the doors and ensure smooth operation. It is important to note that coordinators are not always required, and their use depends on the specific door configuration and code requirements.
Strike Plates and Dust-Proof Strikes
Strike plates are essential components that receive the extended flush bolt when the door closes. The source material mentions the use of dust-proof strikes for the bottom bolt of a flush bolt system. While these are not required by code, they can contribute to a cleaner and more aesthetically pleasing installation by reducing dust accumulation.
Recessed and Surface-Mounted Options
Depending on the door material and design, flush bolts may be either recessed into the edge of the door or surface-mounted. The source material provides an example of a metal double-door system using the DF330 flush bolt, which is installed using M8 screws and requires separate rods for operation. For wood or metal doors, a lever-action flush bolt may be recessed into the top and bottom edges of the door.
Mounting Hardware and Accessories
Installation of flush bolts typically involves the use of mounting hardware such as threaded rods, mounting screws, and guide plates. These components help to secure the flush bolt in place and ensure that it operates smoothly. The source material also notes that for lever-action flush bolts, additional components such as strike plates and bolthead guide plates may be necessary.
Compliance and Accessibility Considerations
When selecting and installing flush bolts, compliance with applicable codes and standards is essential. The source material highlights several key considerations related to egress, fire safety, and accessibility.
Egress and Fire Safety
In certain applications, flush bolts must be designed to ensure safe egress in case of emergency. Automatic flush bolts with auxiliary fire pins are an example of how this can be achieved. These devices are designed to project when exposed to high temperatures, helping to prevent the door from being opened during a fire.
For doors serving storage or equipment rooms, manual flush bolts or surface bolts may be permitted, provided that the space is not required for egress. However, for high-occupancy or high-risk environments, automatic or panic hardware is typically required to ensure that occupants can exit quickly and safely.
Accessibility Standards
Accessibility is another critical factor when selecting flush bolts for doors in public or accessible spaces. Manual flush bolts require the user to grasp and pinch the lever, which may not be feasible for individuals with limited dexterity or mobility. As a result, manual flush bolts are not recommended for accessible routes or spaces that must comply with ADA standards.
In such cases, automatic flush bolts or panic hardware should be used. These devices allow for easier and more accessible operation, ensuring that individuals with disabilities can use the doors without difficulty.
Conclusion
Flush bolt installation is a complex process that requires careful consideration of door type, function, and compliance requirements. The source material provides a comprehensive overview of the different types of flush bolts, their applications, and the necessary installation components. By selecting the appropriate flush bolt type and ensuring proper installation, building professionals can enhance door security, improve accessibility, and meet fire and egress requirements.
For those responsible for specifying or installing flush bolts, it is essential to consult applicable codes, standards, and the authority having jurisdiction (AHJ) to ensure compliance. In addition, using high-quality components such as coordinators, strike plates, and mounting hardware can contribute to a more reliable and long-lasting installation.