Fire-resistive construction involves the use of passive means to provide fire resistivity to specific elements of the building that require additional protection in a fire. Fire protection by passive means is the use of walls and floors constructed of fire resistive materials, opening protections, and penetration protection assemblies to prevent the passage of heat, fire and smoke for a specific time period without the use of active measures such as automatic fire sprinkler systems.Fire resistive walls can be classified into three different types of assemblies to resist fire: fire walls, fire barriers and fire partitions. Each of these types have an increasing level of protection, with fire walls providing the greatest protection.We will cover three main categories:
Fire Walls
In the building code, a fire wall is defined as:
[BF] FIRE WALL. A fire-resistance-rated wall having protected openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof, with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall.
Fire walls provide protection of one building or portion of a building for the condition where the building on the other side is fully engulfed in flames and could be subject to complete collapse. The concept originated in densely populated urban areas where buildings were built directly against lot lines, which is used to this day.Fire walls, covered in Section 706, use a number of methods to provide this highest level of fire protection. They use parapets, fire wall extensions beyond the face of the building, and higher fire-resistance ratings as compared to other types of fire assemblies. Fire walls more strictly limit openings allowed and are typically constructed out of non-combustible materials, unless the type of construction of the building is Type V.
A primary feature of fire walls not found in other fire-resistive walls is the requirement that the wall be designed with the structural stability to allow collapse of the structure on either side without collapse of the wall itself under fire conditions. Fire walls constructed in accordance with NFPA 221, which is a standard by the National Fire Protection Association for fire walls, are considered to meet this standard. However, it should be pointed out that the building code does not require construction in accordance with NFPA 221 to be a proper fire wall. NFPA 221 provides a number of requirements beyond what the building code specifies. However, a design for proper structural stability should take into account a number of factors that NFPA 221 recognizes. These include:
- stability under applied design loadings including applicable out-of-plane loadings
- stability due to forces from the collapse of the adjacent structure, including pulling away of materials, decking or the collapse of items such as storage racks onto the wall during a fire
- stability and integrity of the wall due to expansion of materials during the fire due to heat
- consideration of the 5psf out of plane loading under typical conditions
Fire ratings of walls are based on the adjacent occupancies found adjacent to the wall. In addition, the ratings of fire walls should be checked against Table 602 for fire walls adjacent to lot lines. In addition, specific fire ratings are required for any openings in fire walls, such as those found in Table 716.1\(2\) based on the fire rating \(in hours\) of the wall itself.UpCodes Code Calculators help determine the required ratings for fire walls based on occupancy group and type of construction, as would be found in Table 706.4.
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Fire Barriers
A second type of fire-resistance rated wall assembly is a Fire Barrier. Fire barriers are defined as:
[BF] FIRE BARRIER. A fire-resistance-rated wall assembly of materials designed to restrict the spread of fire in which continuity is maintained.
Fire barriers provide fire-resistance to items that are critical items to the life safety of the occupants, including shaft enclosures, interior exit stairway and ramp construction, enclosures for exit-access stairways, exit passageways, horizontal exits, atriums, incidental uses, control areas, separated occupancies, and fire areas. Fire barriers are typically on a particular story of the item in question, and extend from either the foundation or floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above. Shafts and exit enclosures are permitted to terminate at the top of the enclosure complying with specific requirements.
Construction of fire barriers can be either non-combustible or combustible construction in accordance with the type of construction of the building. Supporting construction (such as beams or other structural floor systems) is required to be equal to the fire-resistance rating of the fire barrier supported. There are exceptions for incidental uses and walls separating tank storage. If a concrete slab or other member is used for support of walls, the architect should review Section 721and coordinate with the structural engineer to ensure the properly sized member or proper concrete cover for slab reinforcement or tendons (in post-tension construction) is provided for the hour rating required for the fire barrier.
Fire barriers provide a more generous allowance for openings in walls than do fire walls. However, there are a number of restrictions and requirements for openings in fire barriers. Membrane penetrations, through penetrations, joints at intersections of fire rated assemblies and floor or roof/ceiling assemblies, fire doors and fire window assemblies all have specific requirements depending on the use of the fire barrier and the type of item used. For example, fire-resistance rated glazing tested in accordance with ASTM E119 or UL 263 does not have to meet the requirements for fire protection glazing because it meets the requirements of a wall, but fire protection glazing tested in accordance with NFPA 257 or UL 9 shall meet the requirements of Section 716.1.2 for glazing. Because each item in a fire barrier is a potential point of weakness, and just a small failure can have catastrophic results, it is important to dig into each requirement to ensure that the minimum requirements of the code are met or exceeded. These are recognized as being so critical, that special inspections are required per Section 1705.17 in high-rise buildings and those buildings of Risk Category III or IV for through-penetrations, membrane penetration firestops, fire-resistant joint systems and perimeter fire barrier systems. Also, for fire barriers or any fire-resistant construction, when there is an accessible concealed floor, attic space or other space where maintenance or other trades could install unprotected penetrations in the wall, a stencil identifying the wall as such is required per Section 703.7.
If Fire Barriers are used to separate the building into fire areas, UpCodes Code Calculators will show the required ratings for such fire barriers in accordance with Table 707.3.10 based on occupancy groups provided.
Fire Partitions
Fire partitions provide the most basic level of protection against fire. They are used to separate dwelling units, tenant spaces in mall buildings, corridor walls, elevator lobby separations and egress balconies. Fire partitions may be of any material permitted by the building type of construction, and typically have a fire-resistance rating of 1 hour. However, dwelling or sleeping unit separations in Buildings of Type IIB, IIIB and VB construction may have ½ hour fire-resistance ratings when an NFPA 13 automatic sprinkler system is installed.
Fire partitions are continuous from the floor/ceiling assembly below and extend to either the underside of the roof or floor sheathing or deck above, or to the underside of a floor or roof/ceiling assembly having at least the same fire rating as the assembly itself. There are specific exceptions for corridor walls to allow for what is commonly called “tunnel construction”. Tunnel construction allows for the ceiling membrane of the corridor to be equivalent to the corridor wall membrane. This is allowed provided that the room side membrane extends to the underside of the floor or roof sheathing, or the building is equipped with an NFPA 13 or 13R automatic sprinkler system and sprinklers are installed between the top of the fire partition and the underside of the roof or floor sheathing or deck above. Alternatively, tunnel construction with both a lower and upper membrane matching the wall construction is allowed where the corridor ceiling assembly matches the corridor wall assembly. Wall assemblies can be found in Table 721.1(2) which shows the prescribed assembly in which to obtain various fire ratings ranging from one to four hours.
Supporting construction for fire partitions such as beams, columns or floor joist assemblies shall have a rating to match the rating of the wall. However, this does not apply to buildings of Type IIB, IIIB and VB construction, since such a requirement would have the effect of making a great deal of the building fire resistant construction, contrary to the non-rated nature of Type IIB, IIIB and VB construction.
UpCodes Code Calculators can help determine the fire-resistance rating requirement for corridor walls based on the sprinkler system and the occupancies that are designated as being served by the corridor.
UpCodes Code Calculators
UpCodes Code Calculators provide powerful tools to be able to determine a number of code requirements rapidly. They also provide the ability to adjust parameters quickly to discover how compliance with code requirements change as a project changes. Other features include allowable area and height calculators, egress calculations with cumulative loading features and exporting code sheets for use in your construction documents. These code reports are exported to an excel spreadsheet that will provide all generated code information in an easy to understand format for use in your construction documents.
Please note we’ve used the Wyoming Building Code for the examples above as it shares much in common with many other state and city codes. Please reference your jurisdiction’s codes for amendments specific to your project.