Residential Roof Insulation—A New Headache
George Howard’s training notebook
Almost any firefighter who has vented a commercial or flat roof has had his saw blades stalled or gummed up with layers of asphalt and insulation. How many times has he cut that nice 4 X 4-foot hole only to find another layer of roof below? Ask that same firefighter about cutting a residential roof and he’ll probably tell you that an axe is man’s best friend.
Not so fast.
With the increasing cost of oil and gas, homeowners and builders are constantly looking to save energy, and more efficient methods of insulation are continually being developed. One area in which great strides recently have been made is residential roof insulation. Unfortunately, along with these strides, the fire service will be running headlong into new problems.
To better understand some of the problems we will be facing, let’s review the basic structure of a typical frame house, in particular, the roof area. Generally, the rafters are a minimum of 2 X 6 inches, 16 inches or more on center, and rest on the outer walls on one end and are joined at the ridge pole at the peak.
Laid over the rafters are the sheathing boards. The sheathing boards of newer houses are of plywood, with a minimum thickness of 3/8 inch, as recommended by shingle manufacturers. Older homes, prior to the early 1960s, typically have 1 X 6-inch tongue and groove planking. (Cedar shake shingles were generally laid over 1 X 2-inch furring strips and are not discussed here.) The sheathing is covered by a vapor barrier of 15-pound felt material and then the roof covering is laid. The roof covering can be shingle, slate, tile, or whatever the builder or architect decides to use. If cheaper strip shi ngles are used, a second or third roof may be added as the original roof quickly weathers and ages.
Beneath this structure is the attic or void area. If necessary to ventilate, holes could be easily cut with an axe. The sheathing is solid enough so that the axe doesn’t bounce, yet thin enough to yield to a few well-placed blows. Using a power saw on a pitched roof is not safe unless operating from the basket of an elevated platform.
Recently, new types of roof insulation boards have been developed for use on residential structures. They consist, basically, of urethane foam bonded to 7/8-inch wafer board. Thickness of the foam varies from 1 1/2 inches to 4 inches. The boards are manufactured in 4 X 4-foot and 4 X 8-foot sheets.
The insulation is applied directly on top of the sheathing of the structure, with the wafer board side out. The foam is sandwiched between the sheathing and wafer board. The wafer board serves as the nailing base for a vapor barrier and the new roof covering (see figure). Once the roof covering is in place and the fascia and trim boards are installed, you cannot tell the difference between the new type and the older type of roof.
Pre-planning is probably the best method of determining if any buildings in your response area are being built with this type of insulation. When such a condition is known beforehand, alternate methods of ventilation should be studied and planned due to the amount of manpower required, which may be better utilized elsewhere.
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TRAINING NOTEBOOK
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In some instances, this type of insulation may be installed by the homeowner when remodeling or re-roofing. In this case, the firefighters would first learn of this condition when they attempt to vent the structure. The importance of understanding this type of roof insulation, its inherent problems, and the need to communicate its discovery to the incident commander cannot be overemphasized.
For the truck company, or those members charged with ventilation, this type of roof presents some additional problems. The flammability of the urethane foam may provide the possibility of a self-sustaining or core fire between the boards.
Normal ventilation procedures with an axe would probably prove timeconsuming and ineffective due to the resiliency of the foam and the thickness of the wafer board. An axe would tend to bounce off the board, especially with the thicker foams, and if it did succeed in penetrating the wafer board, it would still have to cut through the foam and another layer of wood, the sheathing. A circular saw may be more useful with this type of roof insulation, but with its limited depth of cut, two sets of cuts may have to be made. A chain saw with its longer blade would be useful, but more dangerous. Again, remember the extra hazard of operating a power saw on a peaked roof.
Another method, albeit very timeconsuming, is to remove a section of the roof covering. Find a corner of the insulation board and pry it up with pike head axes, halligan bars, or other prying tools. As the boards are either 4 X 4-foot or 4 X 8-foot sheets, a sizable section of the lower sheathing can be uncovered, and then a hole could be cut in the original sheathing.
If the decision is made to vertically vent a structure with this type of insulation, self-contained breathing apparatus (SCBA) must be worn, as urethane foam is highly toxic and generates a great deal of thick, black smoke. The officer in charge of roof operations should be watchful of fire extension into the foam core, both before and after ventilation. Stretching a handline to guard against such extension would be a wise move. Keep in mind that smoldering insulation may burst into flames when peeled away from the roof and exposed to fresh air.
Truck companies may have to spend more time performing extensive roof overhaul to examine for and to extinguish spot fires in the foam. Studies have shown that insulated structures may experience faster failure of exposed members (e.g., rafters, joists, and studs) due to the increased heat retention.
Engine companies and rescue teams are not immune from the problems caused by this type of insulation either. As the insulation’s primary purpose is to retain heat, something it does very well, greater interior temperatures and a greater possibility for flashover can be expected. The need for proper protective clothing, SCBA, and communication cannot be overemphasized.
When faced with this type of roofing in a fire situation, the incident commander must carefully utilize his resources and manpower. The need for vertical ventilation should be weighed carefully, taking into consideration the need for additional engine and truck companies and the possibility of structural collapse. If possible, and if prudence dictates, horizontal ventilation of the attic and void spaces, assisted by a hose line, may prove more effective.
Once again, no matter which ventilation tactic is chosen, it is imperative that all involved wear SCBA and that precautions be taken against fire extension into the foam core.
As the availability and use of this type of insulation increases, more problems are bound to arise. It is incumbent upon the fire officer to familiarize himself with this and other new developments in building construction, and to know where they are used in his response district. Pre-planning is a great asset in learning of and dealing with these developments. Local building supply houses and contractors are also a good source of information. For more technical data, you may want to refer to the National Fire Protection Association’s FIRE PROTECTION HANDBOOK, fifteenth edition.
