BY FRANCIS L. BRANNIGAN,SFPE (FELLOW)
Editor’s note: For further reference, consult Building Construction for the Fire Service, Third Edition (BCFS3). Page numbers, where applicable, are included after the caption.
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Sheathing is the first material to be attached to a building’s wood framing. Years ago, houses were built with diagonal sheathing that provided dimensional stability and wind resistance. The waste it involved was costly, and so it was abandoned.
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This building is sheathed in plywood. Today, many buildings are sheathed in oriented strand board (OSB), which consists of chips of wood glued together.
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This building is sheathed in combustible low-density fiberboard.
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This interior view shows the warning label “Caution: Combustible. May smolder or burn if ignited.” When the interior gypsum board is installed, it covers up the fiberboard. A plumber using a torch to sweat a copper pipe may ignite the gypsum board paper cover and put the fire out with a little water. However, sometimes the fire may be communicated to the sheathing and break out hours later. Plumbers should be cautioned that such fires, even if apparently extinguished, should be reported to the fire department, which can use a thermal imaging camera to determine if there is hidden fire. A propane torch used improperly in the installation of a membrane roof caused a fire that destroyed the building and contents. (See NFPA Journal, May/June 2004, 18.)
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Siding is the material seen on the exterior of the building; here it is brick veneer. This is not “another type of brick building”—it is a wooden building with a brick veneer siding. The siding is totally dependent on the wooden building for stability. (For more information, see BCFS3 Index, p. 650, “Brick veneer.”) An FDNY officer was killed by the collapse of an imitation stone veneer siding when the structure suffered an interior collapse. The occupants may feel safer in a “brick” as opposed to a wood-frame building, but they are not, and neither are firefighters.
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This building is sheathed in gypsum sheathing, which when combined with brick veneer, helps to achieve a rating for resistance to exterior exposure. In this Texas case, a huge mansard is erected on the exterior. An interior fire could burn through a window casing and run freely on the sizable interior surface of the plywood, out of the fire department’s reach. It appears that it would be impossible to fight such a fire safely because of the certainty that the plywood and its wooden support structure will collapse.
Additional information on the hazards of siding can be found in Chapter 3, “Wood Construction,” under “Siding,” pp. 120-124, in BCFS3.
FRANCIS L. BRANNIGAN, SFPE (Fellow), the recipient of Fire Engineering’s first Lifetime Achievement Award, has devoted more than half of his 60-year career to the safety of firefighters in building fires. He is well known as the author of Building Construction for the Fire Service, Third Edition (National Fire Protection Association, 1992) and for his lectures and videotapes. Brannigan is an editorial advisory board member of Fire Engineering.
