Article and photos by Gregory Havel
Many buildings have double roofs. Those of most concern to firefighters are not those to which a second layer of shingles or roof membrane have been added to prevent rain and snow from entering the building. Although these additions provide additional fuel if there is a fire, they do not substantially affect vertical ventilation performed with modern power tools.
Firefighters need to be concerned about the type of double roof that is installed to give the building a different look in addition to preventing rain and snow from dripping through the ceiling.
Photo 1 shows a building that originally had a flat roof. Trusses and plywood sheathing were added to create a new roof that is pitched to both the B and D sides rather than to the rear (C side). A mansard has also been added to the front and front corners of the building.
(1)
Photo 2 shows a building that originally had a flat roof. Trusses and plywood sheathing were added to create a new roof that is pitched to both the B and D sides, rather than to the rear (C side). This addition is more obvious than most double roofs–the builders usually raise the tops of the side walls to make them and the roof line level.
(2)
Photo 3 shows part of a 1940s-era residence during remodeling in 2004. A new wing was added to the house in the 1970s; the ridge of the addition was matched to the ridge of the original house. This addition created a concealed space in which the floor is part of the original, sloped, wood-shingle roof.
(3)
In addition to giving the building a different appearance, these new roofs and the mansard have also done the following:
- added combustible concealed spaces that may be connected to existing concealed spaces throughout the rest of the building.
- trapped a significant amount of combustible materials (the old, dry roofing materials) inside the concealed spaces.
- changed the way in which a fire will behave in this building.
- made vertical ventilation a more difficult and more hazardous option.
When commercial buildings like those in Photo 1 and Photo 2 are known to have double roofs or mansards, this deserves a note on the building’s preincident plan.
Several reports from the National Institute for Occupational Safety and Health (NIOSH) Fire Fighter Fatality Investigation and Prevention program show that double roofs that were not recognized during incident operations have contributed to several firefighter fatalities during the past few years. These reports are available at http://www.cdc.gov/niosh/fire. This Web site also has a link to subscribe to e-mail notices from NIOSH each time new reports are published.
In a residence or a commercial building not known to have a double roof, unexpected fire behavior should suggest to you that the structure has been modified and that fire is spreading through the concealed spaces. You need to change your strategy and tactics to address this threat rather than continuing the strategy and tactics that are not working as they should.
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