Fire-Resistive Construction (2nd part) Session 14 | Codes | Gary Parker IBC Chapter 7 Fire-Resistive Construction (2nd part)

Fire Barriers Fire barriers FB are similar to FW but with simpler criteria. They are used to separate vertical exit enclosures from other egress components, to separate different occupancies, or to divide a single occupancy into different fire areas. FB serve to separate vertical exit enclosures from other egress components.

Fire Barriers FB serve to set apart different occupancies, or divide a single occupancy into different fire areas. Walls located on the outside of the building at rated enclosure may have a different rating than the walls facing the interior of the building. Exterior wall ratings are determined by exterior criteria according to §704 as well as exit requirements of §1005.3.4

Fire Barriers FB are to be continuous between floor levels and extend to abut adjacent interior or exterior walls. The intent is that the FB prevent the spread of smoke or fire for the duration of the time rating. Penetrations and openings are permitted but must be protected to maintain the integrity of the FB. FB should extend from the top of the floor assembly below to the underside of the floor or roof deck or slab above. FB should be continuous through concealed ceiling spaces. Supporting floor should have the same fire rating as the fire barrier supported.

Shaft and Vertical Exit Enclosures §707.2 states that all openings through floor/ceiling or roof/ceiling assemblies will be protected. Shaft enclosures differ from FB in that they typically enclose shaft extending through several floors. The required rating for shafts is usually determined by the number of floors they interconnect. Shafts should be of 2-hr rating if extending four stories or more and 1-hr otherwise. Shaft ratings are equal to those of the floor assemblies but need not be >2hr. Vertical spaces within shaft enclosures should be fire-blocked at each floor level.

Shaft and Vertical Exit Enclosures – Exceptions to §707.2 1 - Openings in residential units extending less than 4 stories need not be enclosed. 2 - Escalators and stairs not used as means of egress need not be enclosed in fully sprinklered buildings with a draft curtain around the floor opening. This exception applies for <= 4 stories except Group B and M where there is no height limitation. The opening dimension should not exceed twice the size of the escalators or stairs. For cases with power-operated shutters with 1.5 hr ratings, there is no limit for the number of floors that can be penetrated. 3 - Pipe, vent or conduit penetrations protected at the floor or ceiling according to §711.4 need not be protected. 4 – Ducts protected as per §711.4 also need not be protected.

Shaft and Vertical Exit Enclosures – Exceptions to §707.2 5 – Floor openings in buildings considered as covered malls or atria need not have shaft protection, however, these occupancies require meeting many other specific fire protection requirements. 6 – Chimneys need not be in a shaft, but concealed spaces should be blocked. 7 – Openings that do not connect more than 2 stories and that are not part of a means of egress may be open, even in buildings not equipped with fire-sprinklers 8 – Ramps for automobiles in parking garages may be open when the criteria of §406.3 and 406.4 for open or enclosed parking garages are met. 9 – openings connecting mezzanines and the floor below need not be enclosed. 10 – Expansions or other joints need not be enclosed, but they should be protected as per §712.

Shaft and Vertical Exit Enclosures Shafts must be fully contained. In cases when a shaft does not fully extend to the floor above or below, it must be enclosed at the top or the bottom. These enclosures may be of the same fire-rating as the the last floor penetrated but not less than the rating of the shaft. Shafts may terminate in a room related to the purpose of the shaft, which must be enclosed by the same construction and with the same rating.

Shaft and Vertical Exit Enclosures – Laundry Chutes Refuse and laundry chutes need be separated from the rest of the building with 1-hr rated access rooms on each floor and with 1-hr termination rooms at the bottom of the shaft according to §707.13. Active fire protection is also required as per §903.2.12.2

Shaft and Vertical Exit Enclosures - Elevators While §707.14 requires that elevator shafts be built as other shafts, it adds requirements for elevator lobbies at fire-rating as corridors according to §1004.3.2.1. The lobbies are to be constructed as for other fire barriers with opening protectives and a means of egress. Elevator lobbies are required where an elevator opens onto an exit access corridor. The exceptions to the elevator lobby requirements are: 1 – For office buildings, when the building lobby level is sprinklered, the street-level lobby may be open without elevator lobby enclosures. 2 – where shafts are otherwise not required per the exceptions to §707.2 3 – Doors that enclose elevator shaft for sealing off the shaft from smoke and fire may be substituted for lobbies when they comply with §3002.6 4 – Lobbies may be omitted for up to 3 stories above the lowest level of fire-department access.

Fire Partitions Fire partitions FP are the next level of fire-resistive wall construction below the FW and FB. They typically have 1-hr fire-resistance ratings and are primarily used for separation between dwelling units and guest rooms §310.3; for separation of tenants in a covered shopping mall §402.7.2 ; and for exit corridors §1004.3.2. FP have similar relationship to exterior walls as FW and FB. They also have similar requirements for penetrations, openings and ductwork as for other groups of partition types. While FP are to extend to the structure above and below, there are exceptions contained in §402.7.2.

Fire Partitions - Exceptions 1 – When the floor is 1-hr rated, the partition need not extend into the crawl space below. 2 – When the room-side fire-rated membrane of a corridor extends to a fire-resistive floor or ceiling above, the corridor ceiling may be protected, as for a 1-hr rated floor/ceiling assembly. 3 – When the walls and ceiling form a tunnel, the fire rating need not extend above the top of the ceiling assembly.

Fire Partitions - Exceptions 4 – In covered mall buildings, as defined in §402.7.2 , fire-rated assemblies need not extend above the ceiling line of the tenant spaces. The ceilings are not required to be rated in such conditions. 5 – The fire barrier forming the separation between dwelling units in Group R-2 occupancies need not extend into the attic is draft-stopped at every 3,000 sf or every 2 units, whichever is the smaller. 6 – If combustible floor/ceiling or roof/ceiling spaces are sprinklered, fire-blocking or draft-stopping will not be required.

Smoke Barriers §709 treats smoke barriers as FB, but with emphasis upon restricting the spread of smoke. Smoke barriers SB are required to have a 1-hr rating with 20-minute-rated opening protectives. SB need not be continuous through concealed spaces unless they touch assemblies that will resist the passage of smoke, such as walls meeting fire-rated ceiling assemblies.

Horizontal Assemblies §710 defines horizontal assemblies HA as floor/ceiling assemblies and roof/ceiling assemblies that require a fire rating. The rating is determined based on construction as dictated by Table 601. When separating occupancies or dividing a single occupancy into fire areas, the rating of the HA must also be examined against the requirements of Table 302.3.3 §710.3.2 permits lower membranes to be omitted over unusable crawl spaces and upper membranes to be omitted below unusable attic spaces in 1-hr rated floor constructions. Unprotected skylight openings are allowed when separation requirements to adjacent structures are met according to §704.10 and the integrity of the roof construction around the skylight opening is maintained as for the rest of the roof. Any structural members or walls supporting a horizontal assembly must have at least the same fire-resistance rating as the horizontal assembly.

Penetrations §711 requires that penetrations be protected to maintain the fire-resistive integrity of the assembly being penetrated. Penetration treatment requirements are based on the size and quantity of penetrations. Exceptions allow for certain small pipes or electrical components of specified sizes. Penetrations are of two basic types. One is a through penetration that passes through an entire assembly. The other is a membrane penetration that goes through only a portion of an assembly.

Penetrations Sleeves must be fastened to the assembly penetrated Any space between the sleeve and the penetrating item, and between the sleeve and the assembly penetrated must be protected by an approved fire-stop material or system Fire-stop system for through penetrations must have an F rating at least equal to the fire rating of the assembly penetrated. Concrete grout or mortar may be permitted to act as a fire-stop around penetrating items through concrete or masonry walls.

Penetrations §711.3.2 limits the size of steel electrical boxes and requires that they be separated by a horizontal distance of not less that 24”, or by a horizontal distance not less than the depth of the wall cavity filled blocking.

Penetrations Horizontal Assemblies The criteria are more stringent given the probability of spread of smoke by convective forces. Ducts are required to be treated as penetrations and the spaces around to be sealed. Recessed lighting fixtures shall not reduce the rating of floor/ceiling assemblies that are required to have a minimum of 1 hr rating.

Penetrations The space around a noncombustible item that penetrates only a single rated floor need only be filled with an approved material The noncombustible item may penetrate multiple rated floors if limited in size according to §711.4.1 §711.4.3 requires that even non-rated horizontal assemblies have spaces filled to resist the free passage of smoke and flame. In this case penetrating items may connect no more than 2 stories. Noncombustible items may penetrate no more than 3 stories.

Joint Systems Expansion, seismic movement and construction control joints are treated in a similar manner to penetrations, §712 The goal is to maintain the fire-resistive capabilities of horizontal and vertical assemblies where joints occur. Joints in rated assemblies are to be fire tested to match the assembly rating before and after movement. Expansion joints are to have fire-resistance as for other penetrations. Joints at the intersection of floor assemblies and exterior curtain walls are included in §712.4. These intersections are to be sealed with approved materials.

Fire-Resistance of Structural Members §713 requires that the ratings of structural members comply with the requirements for the types of construction set forth in Table 601. §713.2.1 requires individual structural members to be fully protected on all sides for their entire length in case they are required to be rated and either support direct load from more than 2 floors or a floor and a roof, or support a load bearing wall or a non-load bearing wall more than two stories in height.