Note: the codes discussed in the following paragraphs do not pertain to single family dwellings in most jurisdictions. However, they serve as an excellent guideline to anyone planning a new home built to higher levels of fire safety.
Introduction
Reference: UBC Sec. 17, BOCA Sec. 400406, NFPA 220 (or 101
A-6-2.1)
There are other key issues to be considered in construction or assembly. These issues center around the longevity or structural integrity during a fire. Even though certain building materials and assemblies may be considered noncombustible, their fire performance leaves a lot to be desired. This is due to structural strength loss when exposed to high temperatures, warping, and/or heat conductivity. Some materials crumble when exposed to high temperatures while others warp, sag and melt. All assemblies should be tested in the E-119 standard time and temperature curve test chamber for their longevity in a fire. Fire safety is an important concern in all types of construction. Information on the fire safe use of wood in construction is covered in this chapter. This includes fire performance characteristics, such as ignition, charring, flame spread, heat release, and smoke. When evaluating fire safety, basic data are needed on performance characteristics of building materials. Even more important than the performance of these materials is the design of the building. Therefore, methods are discussed for improving fire safety through design and fire retardant treatments that can improve the fire performance of wood. Major building codes generally recognize five classifications of construction based on types of materials and required fire resistance ratings. Of the five, wood is permitted in three of the classifications. These three types of construction have traditionally been referred to as heavy timber, ordinary, and light frame. Heavy timber construction has wood columns, floors, roofs and interior partitions of certain minimum dimensions. For example, beams and girders may be not less than nominal (6) inches in width and not less than nominal (10) inches in depth. Ordinary construction has smaller size wood members, such as nominal (2) inch thick wood joists. In both heavy timber and ordinary construction, the exterior walls are of noncombustible materials. In light frame construction, the walls, floors, and roofs may be nominal (2) inch thick wood framing and the exterior walls may be of combustible materials. The fire resistance of light frame and heavy timber construction will be discussed later. While the other two classifications, fire-resistive and noncombustible constructions, basically restrict the construction to noncombustible materials’ fire retardant treated wood is permitted in limited applications.
The option to approve alternatives is provided by the following codes: BOCA Sec. 107;
UBC Sec. 105; NFPA 101 Sec. 1-5
The high level of national concern for fire safety is reflected in limitations and design requirements in the building codes. The codes provide the minimum statutory requirements for fire safety. Adherence to codes will result in an improved level of fire safety. Code officials should be consulted early in the design of a building, because the codes offer alternatives. For example, floor areas can be increased with the addition of automatic sprinkler systems. Code officials have the option to connects with the wall; (2) fire-stops at each floor level in partitions that are continuous through two or more stories: (3) fire-stops at all interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings, and cove ceilings; (4) headers at the top and bottom of the space between stair carriages; (5) mineral wool or equivalent noncombustible material packed tightly around pipes or ducts that pass through a floor or a fire-stop; and (6) self-closing doors on vertical shafts such as clothes chutes.
Figure 2 Draft-stops in multifamily buildings. Top, in floor/ceiling assemblies and bottom, in attics, mansards, overhang, or other concealed roof space above and in line with tenant separation when tenant separation walls do not extend to the roof sheathing above ;( NFPA).
Draft-stops are barriers in large concealed passages. New design and construction techniques such as suspended or dropped ceilings and parallel chord trusses have resulted in new draft-stop requirements. Draft stopping materials include 1/2 inch gypsum board and 3/8 inch plywood. Two locations where draft-stops should be used to break up a large area are floor-ceiling assemblies in which the ceilings are either suspended below solid wood. Joists and/or open-web trusses and attics and other concealed roof spaces such as mansards and overhangs. Some construction practices increase the risk of a fire spreading to the concealed spaces. Installing cabinets shower stalls and other structures without an interior wall lining on the studs allow easier penetration into the wall cavities. A built-in bathtub provides interconnections between two walls and the floor. A thin plywood cover over a trapdoor allows a fire to spread easily to the attic or other concealed spaces.
