Patent Application
20130318904
The invention relates to building structures and, in particular, to a fire resistant membrane.
Mechanical shafts, chases, and stairwells are examples of interior building areas requiring fire rated wall or ceiling membranes. Frequently, such areas have access for their construction available at only one side of the wall or membrane. Known methods and materials for constructing these restricted access membranes can be limited in their effectiveness in achieving satisfactory fire resistance.
The invention provides an effective fire rated membrane construction for walls, ceilings, mechanical shafts, chases, and like structures that can be assembled from one side of the membrane. The construction uses a novel combination of conventional sheet metal framing elements, fire rated wallboard or drywall sheets, and assembly techniques. A layer of the fire rated drywall sheets is secured to light gauge steel “C” studs or like framing elements. A second fire rated drywall layer and optional successive layers is/are separated from the preceding layers by resilient channels or like elements. The channels are oriented at right angles to the studs. The channels allow the successive drywall sheets to be secured with screws that do not penetrate the assembly and, therefore, do not directly transfer heat from one side of the membrane to the other. The air space between layers advantageously retards heat transfer from one layer to another thereby adding to the fire rating capacity of the membrane. The channels, additionally, serve the important function of laterally stabilizing the studs against excessive buckling when they are subject to thermal expansion and their ends are constrained. This stabilizing function can avoid the prior practice of leaving the stud ends spaced from one another or from a receiving track to accommodate thermal expansion and thereby avoid buckling but, unfortunately, limiting the height of the membrane.
The inventive construction is scalable in the sense that additional protection can be obtained by adding layers of fire rated wallboard with or without intervening channels.
The terms wallboard and drywall are used interchangeably in the present disclosure.
A membrane or wall such as shown at 10 in the FIGS. is a “one sided construction” meaning that it is assembled by a person or persons standing or otherwise situated on only one side of the membrane. Such one sided construction can be necessitated by certain building areas and/or conditions that limit access to one side of the membrane. Examples of these situations are high rise elevator shafts, utility shafts, chases and reconstruction where the rating of an existing wall is unknown. The membrane or wall 10 includes sheet steel “C” studs typically made of light gauge stock and fire rated gypsum wallboard sheets 12. The studs 11 are conventional commercially available items as are the fire rated drywall sheets 12. Typically the drywall sheets are of a thickness of ⅝ in. and are available in a 4 ft. width and lengths of 8, 9, 10, 12, 14 and 16 ft. The studs 11 can be any commercially available unit typically ranging from 1⅝ in. to 6 in. in width and ranging in length, for example, between 8 ft. and 16 ft. Dimensions used herein can be substituted with industry metric equivalents. The term membrane, as used herein, comprehends a wall, ceiling or other like structure. Where the membrane serves as a ceiling such as in a corridor or stairwell, the studs 11 can serve as joists. The studs 11 can be used in vertical and horizontal orientations to frame a fire resistant chase or other structure.
The membrane 10 is ordinarily assembled by locating the studs 11, in conventional upper and lower U-shaped tracks (not shown) if it is to be a wall, in parallel relation on 2 ft. centers, for example.
The construction of
After any bracing 16 or 22 and 23 to be used is installed, the studs 11 are covered with a first layer 24 of the fire rated drywall. The layer 24 is attached to the studs 11 with conventional self-drilling drywall screws driven through the wallboard into the sides or flanges of the studs. Thereafter, elongated sheet metal channels 26, preferably of a type called a resilient channel and illustrated in
A second layer 34 of wallboard 12 is installed over the resilient channels. Drywall screws 36 fastening the wallboard 12 to the channels 26 are driven into the web 27 of the channel preferably at locations remote from the studs 11. The length of the screws 36 is adequate to penetrate and hold onto the channel web 27 but insufficient to fully penetrate the first wallboard layer 24.
The described membrane construction 10 affords many benefits towards a high fire rating and greater utility over prior art arrangements. Since none of the screws retaining the layers 24 and 34 penetrate the full thickness of the membrane 10, there is no direct heat conducting path from one side of the membrane to the other and which would create a hot spot to initiate a fire in a combustible. The channels 26, being fixed in cross relation to the studs 11, serve to brace the studs against buckling forces. This function allows the ends of the studs to be assembled tight against the ends of other studs or tight within runner tracks (top and bottom) without gaps for thermal expansion and thereby increase the limiting height. Ends of the studs tight fitted in runner tracks can be screw attached to both runner track legs (flanges) to increase the vertical load capacity of the construction thus further raising the limiting height of the construction. It is expected that this tight end fitted screw fastened construction with heavier gauge studs can be used in load bearing walls when restricted to “Exposed to Fire on Gypsum Board Face Only” applications.
The air space, designated 39, between the wallboards 12 of the layers 24 and 34 serves as an insulator to reduce heat transfer from one board to the other. The perforations 31 in the channel side 28 allow air circulation over and through the channels 26 and reduce direct heat transfer through the channel side 28 from one wallboard to the other.
The illustrated membrane 10 can be supplemented in its fire rating. Depending on the application, another series of channels 26 can be mounted on the second layer 34 in the same manner as the illustrated channel 26 and a third fire rated wallboard can be fixed to this second series of channels 26. Again, it is important that the length of the screws be selected so as to not penetrate the full thickness of the membrane. Alternatively, for lesser requirements, a third layer of fire rated wallboard can be simply applied directly against the second layer 34. In these and other construction variants, it is important that none of the screws extend through the exposed surfaces of wallboard on both sides of the membrane.
It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.
