VENTING SINGLE-PLY ROOFS

VENTING SINGLE-PLY ROOFS

Single-ply roofing systems basically are made up of a layer (or layers) of insulation over the structural roof deck and a single sheet of waterproofing membrane material. The sheets are made of synthetic materials that have characteristics similar to rubber or plastic, range in thickness from 0.030 inches (30 mils) to 0.160 inches (160 mils), and range in size up to 50 feet by 200 feet. The membranes are glued to the insulation, mechanically fastened through the insulation into the structural roof deck, or loosely laid over the insulation. The looselaid membranes are held down by gravel. Single-ply roofs typically are found on flat-roof, commercial structures.

Roofing technology has advanced to meet stricter building codes, fire codes, and EPA restrictions. Durability, aesthetics, and installation costs also have prompted manufacturers to develop new roofing materials and systems. These new products are mostly synthetic materials marketed for installation on commercial, industrial, and institutional buildings. Buildings with single-plv roofs are prevalent worldwide and can be identified through preplanning programs. Information such as the type of roofing system, the thickness of the roofing insulation, and the type of structural roof deck is very useful when performing ventilation operations on single-ply roofs.

MEMBRANES

The membranes can be broken down into four groups:

• Vulcanized elastomer. This group includes neoprene and ethylene propylene diene methylene (EPDM). These membranes have rubber-like characteristics and have been used for roofing since the late 1950s.
• These materials also are used for products such as tires, inner tubes, automotive hoses and V belts, gaskets, and electrical conductor jackets.
• Nonvulcanized elastomers. Included in this group are chlorosulfonated polyethylene (CSPE), chlorinated polyethylene (CPE), polyisobutylene (PIB), and nitrile alloy membranes. These materials also are used in the manufacture of rainwear, tarpaulins, inflatable structures, waterproofing coatings, and automotive ignition wires.
• Thermoplastics. Polyvinyl chloride (PVC) and ethylene interpolymers (EIP) are included in this category. These membranes possess plastic-like characteristics and also are used in the manufacture of plastic food containers, sewage and water pipes, credit cards, and upholstery.
• Modified bitumens. Membranes in this group are a combination of bitumen materials derived from the
• distillation of petroleum or coal products and compatible polymers. Modified bitumen roofing membranes are the thickest of the single-ply materials and have a very smooth surface.

INSULATION

Several types of insulation can be used with single-ply roofing systems. The type and thickness depend on the thermal resistance (R-value) required by the building owner or architect. The most popular types of insulations used include the following:

• Expanded polystyrene insulation (EPS). This material is formed by molding expanded beads of plastic polystyrene polymers into blocks or boards and then cutting them to size. The same polymers are used for extruded polystyrene (an extrusion process is used to form the boards) which can be manufactured up to six inches in thickness. Polystyrene materials ignite easily when exposed to flame, and firefighters must be aware of possible fire extensions under the membrane. Disposable coffee cups,
• ice chests, and packing beads are other uses for polystyrene materials.
• Wood-fiber insulation. Composed of wood or cane fibers, this material is integrally treated with waterproofing binders and compressed into boards. It may not readily support combustion due to the chemical fire retardants impregnated into the wood fiber; however, it will smolder, causing fire extensions under the membrane. Wood-fiber insulation may be up to one inch thick and it may be laminated to an EPS board.
• Polyisocyanurate. This insulation has glass fibers added to provide resistance to fire. The boards are faced with a foil or fiberglass material and are manufactured up to four inches thick. This material w ill be consumed by fire; however, it will not support combustion on its own.

Less common insulations used in single-ply roofing systems are polyurethane foam, cellular glass, and phenolic foam. All these insulating materials are marketed in boards or sheets in various sizes.

SYSTEMS

As mentioned previously, there are many variations to each individual manufacturer’s roofing systems, but the systems can be categorized into three major groups. The membranes and insulations discussed above generally can be found in any of these systems.

• Ballasted roofing system. The ballasted or loose-laid roofing system basically is made up of a layer or layers of insulation loosely laid over the structural roof deck. The membrane sheet then is installed over the insulation, and some type of ballast is used to hold the entire assembly in place. The ballast generally used for this system is loose gravel spread out to achieve 10 pounds per square foot. Concrete pavers, either butted together or interlocked, also may be used to achieve the 10-pounds-persquare-foot ballast requirement.

When ventilating, firefighters first must remove an area of ballast, membrane, and insulation approximately eight feet larger than the planned ventilation opening; for example, if you want a four-foot by four-foot ventilation opening, remove a 12-foot by 12-foot area of membrane and insulation. This allows for a safe, unobstructed working area around the ventilation opening and reduces the possibility that the insulation will ignite.

You can use your boot to trace or outline in the loose gravel the area to be cut. Use a utility knife or pair of scissors to cut the membrane on three sides of the outlined area. Pulling on the membrane in the same manner as a knife is used to cut sheets of plastic allows the knife or scissors to glide through it. Once the membrane is cut, two or three firefighters are needed to grab the loose end of the membrane and peel it back. This method quickly removes a large area of ballast and membrane, exposing the insulation. Do not try to cut the membrane with an axe or power saw . The membrane’s rubber characteristics make an axe ineffective as a cutting tool, and a power saw blade will grab the membrane and possibly jerk the saw out of the operator’s hands. Icing conditions severely hamper the removal of ballast. Striking the ballast with the side of an axe will loosen it enough to cut and peel the membrane.

If concrete pavers are used as ballast, you need to pry several pavers up with a pickhead axe and then remove the surrounding pavers with gloved hands. Interlocking pavers are more difficult to remove; however, once the interlock is interrupted, they easily can be removed with gloved hands. Icing conditions on pavers require damaging several pavers to establish a starting point. Once you find a starting point, prying the pavers should not be too difficult. Once again, remember to remove enough pavers to allow a four-foot by four-foot working area around the entire planned ventilation opening.

(Photos by Tony Papoutsis.)

Once you remove the membrane, you can cut the insulation and structural roof deck with a power saw or hand tools. Step cutting (cutting each layer of insulation consecutively smaller until the roof deck is reached) may be needed when multiple layers of insulation are present.

1. • Protected membrane system. A variation of the ballasted system, this system has a membrane installed over a layer of insulation, and additional layers of insulation are installed over the membrane. The assembly then is covered with a cloth filter sheet and ballasted with loose gravel, concrete pavers, or a tongue-and-groove insulation board coated with a cementitious material. These boards are two feet by three feet and weigh approximately (»() pounds each; they may be strapped together with metal strips.

During ventilation, protected membrane systems using the cloth filter sheet and loose gravel can be removed by the same cut-and-peel method mentioned previously. The membrane, sandwiched between the two layers of insulation, requires an additional cut-and-peel procedure.

The protected membrane system using the insulation board with the cementitious surface is more difficult to remove due to the tight interlocking of the tongue and groove and the cementitious coating. You first must remove the metal strapping fastening the insulation boards together by prying the straps upward, popping the fasteners out of the boards. A power saw is needed to cut through the cementitious coating. It is beneficial to cut the boards at the joints, interrupting the tongue and groove and creating a relief cut, which allows you to operate a pry bar. Additional layers of insulation may be found under the top layer of insulation. More step cutting may be needed to remove these layers of insulation and to expose the membrane. The membrane then can be cut and removed to expose an additional layer of insulation and the structural roof deck.

• Adhered roofing system. This type of system is installed by fastening the insulation to the structural roof deck with metal plates and screws and then gluing the membrane to the insulation surface. This type of exposed membrane system allows you to cut the membrane easily; however, peeling the membrane is more difficult due to the adhesion to the insulation. Once you remove the membrane, you can use a power saw or hand tools to cut the insulation. The plates and screws used to fasten the insulation are designed to provide a high pull-out resistance; removing these screws and plates, therefore, is very difficult. Cut around the plates and pry the insulation from under the plates. Fasteners that remain in the roof deck after the insulation has been removed can be hammered into the deck to prevent you from tripping over them.
• Mechanically fastened roofing system. This category of systems includes exposed membrane systems that use a mechanical device to attach the membrane and insulation to the structural roof deck. Most of these systems use round metal discs or bars that are fastened through the membrane and insulation. These plates or bars are sandwiched between two sheets, where they overlap. Other systems use a snap or button device spaced two or three feet on center throughout the roof. This means that the membrane is loose between the fastening devices and flutters as the wind blows over the roof. These systems also use a membrane that has a polyester reinforcement mat laminated in the membrane itself. The membrane can be cut and removed easily; an additional cut, however, may be needed around the fastening device to release the membrane. Keep in mind that the membrane is loose except for the fastened area. If you cut the mem-

• brane during high-wind conditions, the loose ends of the membrane may flutter violently, which could throw tools, equipment, or firefighters off the roof. Cutting the membrane up to the next row of fastening devices reduces the possibility of violent fluttering; it will not, however, eliminate all fluttering. The procedures for removing the insulation and structural roof deck are the same as those procedures used with the other roofing systems.

SAFETY CONSIDERATIONS AND REMINDERS

For aesthetic purposes, many single-ply roofing manufacturers provide a white membrane on exposed membrane systems. These white membranes seem to blend into the horizon and the surrounding area and produce a blinding glare. You may experience problems recognizing the edge of the roof, skylights, and other openings. Also, dew and ice are hard to detect on these white membranes. You must be aware of these situations and take proper precautions to prevent falls.

• Be cautious when walking on loose gravel; it is easy to lose your footing and fall.
• Exposed membrane is extremely slippery when wet.
• The components used for singleply roofing systems—such as adhesives, insulations, and sealants —are extremely flammable and produce toxic fumes when ignited. Wear full protective clothing and SCBA at all times when ignited single-ply roofing materials are involved.
• The opening cut in the insulation and membrane should be at least four feet larger on all sides of the ventilation opening to prevent ignition of roof components and to provide firefighters with a safe, unobstructed work area.
• When laddering upper levels from a single-ply roof, cut and remove the membrane along with any loose gravel. The ladder’s feet then should be embedded into the insulation to prevent slippage.
• Single-ply manufacturers require a minimum of 10 pounds of ballast per square foot on loose-laid systems, which severely overloads the roof. Additional weight from water, firefighters, and equipment contributes to a major collapse hazard.
• Soft insulation, such as polysty-
• rene, may mask early signs of structural collapse.
• Cutting single-ply membranes and filter cloths with power saws may cause the operator to lose control of the saw, causing injury.
• High-wind conditions will cause violent fluttering of loose membranes, which could throw tools, equipment, or firefighters off the roof. Weight down loose membrane edges with ballast. Cut mechanically fastened membranes to the next row of fastening devices to prevent fluttering from occurring.
• Handlines must be present during any ventilation operation.
• Check for fire extension traveling under the membrane.
• Materials removed from the ventilation opening could blow off the building and possibly injure ground personnel. These materials must be removed from the roof or weighted down.
• Incidents involving the installation of single-ply roofing warrant additional considerations. The cleaners, adhesives, and sealants used during the installation are highly flammable and toxic. These materials usually are stored in large quantities on the roof or in job-site trailers on the ground. Locate and protect these storage areas if they are not involved in the fire. Roofing contractors should have material safety data sheets (MSDSs) at the job site; this is not always the case, however. Incident commanders must treat fires involving single-ply installations as hazardous-materials incidents until the materials involved are known.

Installation procedures require that flammable cleaners, adhesives, and sealants be spread on the roof with paint rollers. The vapors that flash off are heavier than air and can travel to any ignition source. W hen ignited, the resulting fire will spread rapidly to all exposed material, causing a large fire. Any containers near this type of fire usually will become involved also. Fire prevention officers should inspect these projects to ensure that local fire codes for storing these types of materials are followed.