The recent events in Los Angeles and the line of duty death of veteran LAFD Firefighter Glenn Allen who died Friday from injuries he sustained when a ceiling collapsed on him in a house fire late Wednesday night in the Hollywood Hills again gives us pause to reflect on the demands and hazards present at all fire suppression operations in buildings on fire. The past two months have borne consist reports of floor, roof, wall and ceiling collapses leading to firefighter injuries and line of duty deaths.
The importance of maintaining heightened situational awareness, identifying and monitoring suspected or inherent building construction hazards coupled with inherent occupancy risk factors, and aligning those with strategic objectives, incident actions plans and tactical deployment operations. Building Knowledge equating to firefighter safety is still a driving principle that is formulative to all firefighting operations in buildings, occupancies and structures. Let’s take this opportunity to gain some insights into the material that compromises nearly all wall and ceiling membrane systems and assemblies in nearly all buildings, occupancies and structures; that is gypsum board components. I’ve included a number of video clips that center on our discussion, as the videos center on the operation parameters at this extremely large (floor area/square footage) residential occupancy. Most clips have good coverage of the structure and firefighting efforts. Take a few moments to review these clips before you proceed;
Gypsum board is the generic name for a family of panel-type products consisting of a noncombustible core, primarily of gypsum, with a paper surfacing on the face, back, and long edges.
In 1888, Augustine Sackett used plaster of Paris sandwiched between several layers of paper to produce what would eventually become “Sackett Board,” the original gypsum board. By the 1950s, many innovations in gypsum board technology had been developed, including the listing of many fire-resistance rated designs, rounded edges, specialized nails, curved partitions, studless partitions, sound control systems, lightweight gypsum lath, plaster, and gypsum board systems that fueled a boom period for the use of gypsum products in both the residential and commercial construction industries.
By 1955, an estimated 50 percent of new homes were built using gypsum wallboard. Lightweight gypsum board systems permitted the use of lightweight steel in steel framed buildings, which enabled the widespread growth of high-rise residential and commercial construction during the 1960s and 1970s.
Today gypsum board, along with a variety of other gypsum panel products, continues to serve as a preferred building material in both residential and commercial construction for interior walls and ceilings, exterior sheathing, fire-resistant partitions and membranes, and liner material for elevator shafts and stairwells. These properties make gypsum board well suited for building and space types requiring cost-effectiveness as well as fire resistiveness and maintainability.
Gypsum board is often called drywall, wallboard, or plasterboard and differs from products such as plywood, hardboard, and fiberboard, because of its noncombustible core. It is designed to provide a monolithic surface when joints and fastener heads are covered with a joint treatment system.
Gypsum is a mineral found in sedimentary rock formations in a crystalline form known as calcium sulfate dehydrate. One hundred pounds of gypsum rock contains approximately 21 pounds (or 10 quarts) of chemically combined water. Gypsum rock is mined or quarried and then crushed. The crushed rock is then ground into a fine powder and heated to about 350 degrees F, driving off three fourths of the chemically combined water in a process called calcining. The calcined gypsum (or hemihydrate) is then used as the base for gypsum plaster, gypsum board and other gypsum products.
To produce gypsum board, the calcined gypsum is mixed with water and additives to form a slurry which is fed between continuous layers of paper on a board machine. As the board moves down a conveyer line, the calcium sulfate recrystallizes or rehydrates, reverting to its original rock state. The paper becomes chemically and mechanically bonded to the core. The board is then cut to length and conveyed through dryers to remove any free moisture.
Gypsum manufacturers also rely increasingly on “synthetic” gypsum as an effective alternative to natural gypsum ore. Synthetic gypsum is a byproduct primarily from the desulfurization of the flue gases in fossil-fueled power plants. Gypsum board is an excellent fire resistive material. It is the most commonly used interior finish where fire resistance classifications are required. Its noncombustible core contains chemically combined water which, under high heat, is slowly released as steam, effectively retarding heat transfer. Even after complete calcination, when all the water has been released, it continues to act as a heat insulating barrier. In addition, tests conducted in accordance with ASTM E 84 show that gypsum board has a low flame spread index and smoke density index. When installed in combination with other materials it serves to effectively protect building elements from fire for prescribed time periods.
Developed through modern technology as a result of specific requirements, gypsum board is mainly used as the surface layer of interior walls and ceilings; as a base for ceramic, plastic, and metal tile; for exterior soffits; for elevator and other shaft enclosures; as area separation walls between occupancies; and to provide fire protection to structural elements. Most gypsum board is available with aluminum foil backing which provides an effective vapor retarder for exterior walls when applied with the foil surface against the framing.
Standard size gypsum boards are 4ft. wide and 8, 10, 12, or 14 ft. long. The width is compatible with the standard framing of studs or joists spaced 16 in. and 24 in. on center. Some thicknesses and types of gypsum board are also produced as a standard 54 in. width material. Other lengths and widths are available as special order materials.
- Depending on thickness and type of gypsum board, the weight can vary from 2 – 4 lbs./ per square foot
- A typical 4 ft. x 8 ft. sheet of 5/8-in gypsum board can weigh 96 lbs.
- A 4ft. x 12ft. sheet can weigh upwards of 150 lbs.
- In large span designs with attachments varying from 16 inches on center to 24 inches on center with z-strips or resilient channels attached to the structural members; these ceiling panels and assemblies can fail and collapse in a monolithic manner creating a significant safety concern to operating companies below.
- As an example a 12ft x 12ft. monolithic assembly collapse ( single layer-gypsum board only) could have a collapse weight of 500 lbs.
- Add the weight of compromised and attached structural members components, fixtures and insulation and the absorption of added water into the gypsum board from hose streams the combined weight of the collapse area may increase to 800-1000 lbs. Increase the size of the collapse area and the weight impacting operating companies is significant.
The various thicknesses of gypsum board available in regular, type X, improved type X and pre-decorated board are as follows:
- ¼-in. A low cost gypsum board used as a base in a multi-layer application for improving sound control, or to cover existing walls and ceilings in remodeling.
- 5/16-in. A gypsum board used in manufactured housing.
- 3/8-in. A gypsum board principally applied in a double-layer system over wood framing and as a face layer in repair or remodeling.
- ½-in. Generally used as a single-layer wall and ceiling material in residential work and in double-layer systems for greater sound and fire ratings.
- 5/8-in. Used in quality single-layer and double-layer wall systems. The greater thickness provides additional fire resistance, higher rigidity, and better impact resistance.
- ¾-in. Used in a similar manner to 5/8-in.
- 1 in. Used in interior partitions, shaft walls, stairwells, chaseways, area separation walls and corridor ceilings. Manufactured only in 24 in. wide panels and usually installed as an integral part of a system.
Depending on the type and the use, gypsum board is manufactured with a tapered, square, beveled, rounded, or tongue and groove edge. Some gypsum board types may incorporate a combination of different edge types. The fire resistance of gypsum board can be described using three distinct terms: regular core, type ‘X’ core and improved type ‘X’ core.
Regular core gypsum board is made of a noncombustible core material composed mainly of gypsum. Although it does not have the specially enhanced fire-resistive properties of type ‘X’, regular core gypsum board affords a degree of natural fire resistance.
In the 1940s different gypsum board formulations were investigated to increase the naturally occurring fire resistance of regular core gypsum board. A new product was eventually introduced that clearly demonstrated “eXtra” fire resistance, hence the name “type X.” The basic components of type ‘X’ that give it a superior fire resistance are gypsum, glass fibers, and vermiculite.
In the 1960s, further modifications were made to the original successful type ‘X’ formulations of gypsum board used in some systems – particularly ceiling systems – without compromising the fire-resistive qualities. The new product demonstrates additional fire resistance over type ‘X’ core, and thus the term “improved type X” was coined. Gypsum board products make up the predominant portion of a family of materials identified as gypsum panel products. Gypsum panel products are defined as sheet materials consisting essentially of gypsum. They can be faced with paper or another material, or may be unfaced. Gypsum board, glass-faced sheathing materials with a gypsum core and unfaced gypsum-based products are all considered to be gypsum panel products. Technically, gypsum board is defined as the generic name for a family of sheet products consisting of a noncombustible core, primarily of gypsum, with a paper surfacing on the face, back, and long edges. In recent years the family of gypsum-based panel materials has grown to include panel products other than those with the familiar paper facers. A number of specialized gypsum panel products and gypsum boards have been developed for specific uses which include:
- Gypsum Wallboard for interior walls and ceilings
- Gypsum Ceiling Board for interior ceilings
- Type X Gypsum Board for fire-resistance-rated building systems
- Fiber Reinforced Gypsum Panels for interior and exterior walls, ceilings, and tile base
- Gypsum Sheathing for exterior walls and roof systems
- Glass Mat Gypsum Substrate for use as sheathing on exterior walls and ceilings
- Gypsum Soffit Board for use on exterior soffits and ceilings
- Water-Resistant Gypsum Backing Board for use as a tile base
- Glass Mat Water-Resistant Gypsum Backing Board for use as a tile base
- Gypsum Backing Board for use as a base for multi-ply systems
- Gypsum Lath for use as a base for gypsum plaster
- Gypsum Plaster Base for use as a base for veneer plaster
- Gypsum Shaft Liner Board for shaft, stairway, and duct enclosures
- Pre-decorated Gypsum Board for accent walls, office and movable partitions
- Foil backed gypsum board for use as a vapor retardent
Identified by their technically correct names, gypsum board products are as follows: Gypsum Wallboard is produced primarily for use as an interior surfacing for buildings. It is the most often used commodity gypsum board and annually accounts for over 50 percent of all the gypsum board manufactured and sold in North America. Gypsum wallboard has a manila-colored face paper and is manufactured in a variety of thicknesses as both a regular- and a fire-resistant core material.
Gypsum Ceiling Board is an interior surfacing material with the same physical appearance as gypsum wallboard. Gypsum ceiling board is manufactured as a ½-inch thick material; it is designed for application on interior ceilings, primarily those intended to receive a water-based texture finish. It has a sag resistance equal to 5/8-inch thick gypsum wallboard.
Predecorated Gypsum Board has a decorative surface which does not require further treatment. The surfaces may be coated or painted, printed, textured, or have a film – such as vinyl wallcovering – applied. It is manufactured in a variety of thicknesses as both a regular- and a fire-resistant core material.
Water-resistant Gypsum Board is a gypsum board designed for use on walls primarily as a base for the application of ceramic or plastic tile. It is readily identified by its green-tinted face paper and is commonly referred to as “Greenboard.” It has a water-resistant core and a water-repellent face and back paper; it is generally installed in bath, kitchen, and laundry areas.
Gypsum Backing Board, Gypsum Coreboard, and Gypsum Shaftliner Panel are all designed to be used as base materials in multi-layer, solid and semi-solid, and shaftwall systems. Gypsum backing board is used as a base layer for other gypsum board materials in systems or as a base for dry claddings such as acoustic tile. Gypsum coreboard and gypsum shaftliner are manufactured with a type X core, using a specific edge configuration to facilitate installation into specialized stud systems and a type X core.
Exterior Gypsum Soffit Board is designed for use on the underside of eaves, canopies, carports, soffits, and other horizontal exterior surfaces that are indirectly exposed to the weather. It has water-repellent face and back paper and is more sag-resistant than regular wallboard. Exterior gypsum soffit board can be manufactured with a type X core and typically has a light brown face paper.
Gypsum Sheathing Board is used as a backing under exterior siding or cladding. It has a water-repellent face and back paper and can be manufactured with a water-resistant core. Depending on the thickness of the board, gypsum sheathing board is manufactured with either a square or a tongue-and-groove edge and a fire-resistive core. It generally has a brown or light black face paper.
Gypsum Base for Veneer Plaster has a distinctive blue-tinted face paper that is treated to facilitate the adhesion of thin coats of hard, high strength gypsum veneer plaster. It is produced in sheets that are the same width as gypsum wallboard and can be manufactured with a fire-resistive core. Application of Gypsum Board
A wide variety of gypsum board application methods are available to meet virtually any need in building design and construction. Gypsum board is applied in either single-layer or multi-layer systems to achieve specific fire or sound ratings. Gypsum board is applied over wood or steel framing or furring. It is also applied to masonry or concrete surfaces, either laminated directly or attached to wood furring strips or steel furring channels. Gypsum board ceilings can be directly attached to joists or trusses or attached to furring or grid systems suspended below structural members. Gypsum board is generally attached to the framing with nails, screws, or staples. Although nails are commonly used in wood frame construction, screws are often preferred because they are applied with automatic screw guns, have excellent holding power, and reduce the possibility of nail pops. A combination of nails and screws may also be used, with nails along edges and screws in the field. Staples are used because they are economical and can be quickly applied with staple guns; however, the use of staples should be limited to the base-layer in multi-layer systems or to gypsum sheathing on wood framing. Gypsum board wall and ceiling surfaces are typically decorated with paint, texture, wallpaper, tile, or paneling. When pre-decorated gypsum board is used, joints are generally covered with matching molding or battens; no additional finishing or decoration is necessary. Single-Layer Application
- Single-layer gypsum board applications are the most common in light commercial and in residential construction.
- These systems rely on one layer of gypsum board attached to framing or furring.
- Although single-layer gypsum board systems are generally adequate to meet most minimum requirements for fire resistance and sound control, multi-layer systems are preferred for higher quality construction and to upgrade beyond the “bare minimums” of many code requirements.
- Multi-layer systems have two or more layers of gypsum board and are used to meet higher sound and fire resistance requirements or to enhance these comfort and safety qualities beyond minimum code requirements.
- They also provide better surface quality because face layers can often be laminated over base layers eliminating many or all of the fasteners in the face layer. In addition, face-layer joints are stronger by virtue of the continuous backing provided by the base layers.
- Nail pops and ridging are less frequent and imperfectly aligned framing has less effect on the quality of the finished surface.
GYPSUM BOARD TYPICAL MECHANICAL AND PHYSICAL PROPERTIES (GA-235-10) A common misconception is that there are just two basic types of drywall—regular and type X—and beyond this difference, drywall products from various manufacturers are about the same. However, laboratory fire tests by United States Gypsum Company and various independent testing organizations provide strong evidence that there are significant fire-performance differences between drywall products from various manufacturers. It is well known in the construction industry that the single most important characteristic of gypsum drywall is its fire resistance. This is provided by the principal raw material used in its manufacture, CaSO4- 2H2O (gypsum). As the chemical formula shows, gypsum contains chemically combined water (about 50% by volume). When gypsum drywall panels are exposed to fire, the heat converts a portion of the combined water to steam. The heat energy that converts water to steam is thus used up, keeping the opposite side of the gypsum panel cool as long as there is water left in the gypsum, or until the gypsum panel is breached.
- In the case of regular gypsum panels, as the water is driven off by heat, the reduction in volume within the gypsum causes large cracks to form, eventually causing the panel to fail.
- In a special fire test designed to demonstrate the relative performance of different types of gypsum cores (described later in this section), it was shown that in a fire with a temperature of 1,850ºF, a 5/8″ thickness of regular-core gypsum panels would fail in this manner in 10 to 15 minutes.
- Type X gypsum panels, such as Sheetrock brand Firecode gypsum panels, have glass fibers mixed with the gypsum to reinforce the core of the panels.
- These fibers have the effect of reducing the extent of and size of the cracks that form as the water is driven off, thereby extending the length of time the gypsum panel can resist the heat without failure.
- Fire test results indicate that the same thickness of the type X gypsum drywall exposed to the same temperature (1,850ºF) will last 45 to 60 minutes.
USG has developed a third-generation gypsum drywall product called Sheetrock brand Firecode C gypsum panels that provides even greater resistance to the heat of fire. The core of Firecode C contains more glass fibers than type X—but also a shrinkage-compensating additive, a form of vermiculite that expands in the presence of heat at about the same rate as the gypsum in the core shrinks (from loss of water). Thus the core becomes highly stable in the presence of fire and remains intact even after the combined water is driven off. Tests have shown that this third-generation product resisted the fire for more than two hours, as compared to 45 to 60 minutes for the type X, and 10 to 15minutes for the regular panel under the same test conditions.
In a future posting we’ll discuss the issues facing the fire service related to the newest generation of impact resistant gypsum board that will restrict or preclude entirely our ability to breach walls in residential or commercial occupancies. Here are some links and Spec Sheets to look at in advance, HERE , HERE, HERE and HERE
References and Links Summarizing the many different types of gypsum board used in the industry, this quick reference gives typical uses of, and the ASTM and CSA standards for, each type. Also included is the appropriate industry standard designation for the installation of each type of gypsum board, along with the sizes and thicknesses generally available. Download
APPLICATION OF GYPSUM SHEATHING (GA-253-07)
This publication describes the industry’s latest recommendations for handling, storing, and installing gypsum sheathing under a variety of conditions. A must for anyone hanging gypsum sheathing or involved in EIFS work. Download
FIRE-RESISTANT GYPSUM SHEATHING (GA-254-07)
This publication describes the advantages, recommended uses, limitations, and properties of gypsum sheathing in exterior walls.
- Reference guide of construction procedures for gypsum drywall, cement board, veneer plaster and conventional plaster.
Trade Associations and other Organizations
- Association of the Wall and Ceiling Industry (AWCI)—Provides services and undertake activities that enhance the members’ ability to operate a successful business. AWCI represents acoustics systems, ceiling systems, drywall systems, exterior insulation and finishing systems, fireproofing, flooring systems, insulation, and stucco contractors, suppliers and manufacturers, and allied trades.
- ASTM International (ASTM)—Provides a global forum for the development and publication of voluntary consensus standards for materials, products, systems, and services. In over 130 varied industry areas, ASTM standards serve as the basis for manufacturing, procurement, and regulatory activities. Provides standards that are accepted and used in research and development, product testing, quality systems, and commercial transactions around the globe.
- Ceilings and Interior Systems Construction Association (CISCA)—Association for the advancement interior commercial construction, providing education, technical guidance and related resources. CISCA membership includes over 600 of the leading contractors, distributors, manufacturers and independent manufacturer’s representatives worldwide.
- Gypsum Association (GA)—Founded in 1930, GA promotes the use of gypsum while advancing the development, growth, and general welfare of the gypsum industry in the United States and Canada on behalf of its member companies.
- ICC Evaluation Service (ICC-ES)—Provides technical evaluations of building products, components, methods, and materials and issues reports on code compliance to building regulators, contractors, specifiers, architects, engineers, and the public.
Relevant Codes and Standards
- Department of Defense (DoD) Unified Facilities Guide Specifications (UFGS)
- Department of Veterans Affairs (VA)
- Green Construction Specs
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