New Roofs Over Old
BUILDING CONSTRUCTION
If you don’t know there’s another roof under the one you’re ventilating, the results won’t be what you need.
Ventilation is a top priority in successful firefighting operations, but a remodeling project that places a new, independent roof structure over an existing roof will stymie ventilation efforts and pose other dangers to firefighters.
The potential for such a problem has arisen in southwest Ohio because an improvement in economic conditions over the past few years has led to a remodeling boom. The influx of jobs, businesses, and money has spurred a new life for some old, deteriorated structures, from the small corner service station to the block-long building of ordinary construction. In some cases, the buildings’ exterior maintenance had been neglected for many years, allowing severe deterioration of the roof structure and roof covering which led to water leaks into the interior.
In an effort to permanently correct these problems, the owners are placing new, trussed roofs over old, flat roofs. The old roof is left completely intact and usually isn’t disturbed structurally in any way. The void thus created is used for storage (although that’s prohibited by fire codes), filled with insulation, or left empty. Access openings are small and intended for inspectional purposes only, certainly not firefighting.
All of the old roofs we’ve found have been flat, with tar and gravel roofing material which has been built up over the years. It provides a significant fuel load inside an enclosed void that’s not readily accessible.
The old roof decks are made of plywood; one-inch-by-six-inch grooved, wooden planks; or metal. The wooden decks, upon inspection, show severe damage from water leaks and dry rot. Some show signs of sagging, and others have tar visible from below. The metal decks can appear deceivingly intact. But there are areas—the top of the truss and the corners of the building, for example—where water damage can be found; the interior ceilings will also show signs of where the water has been leaking through the roof.
The old roofs can be supported by parallel chord trusses made of wood or steel, or by wooden joists. The metal trusses are generally lightweight steel, such as those found in service stations.
Nearly all of the new roofs have been gable-, hip-, or mansardstyle. Lightweight, wood trusses made from 2-by-4s and secured by steel gusset plates are the design of choice because they’re the most economical. This should bring to mind all the typical red-flag warning signals associated with lightweight, wood truss construction.
The new trusses are set on top of the parapet walls. This places the bottom of the trusses anywhere from 12 to 36 inches above the old roof structure. A two-inch-byfour-inch wooden plate is fastened to the top of the parapet wall with steel anchors, which are set into the walls and cemented into place. The plate is bolted down onto the anchors and the trusses nailed onto the plate. Many projects have trusses toenailed to the plate, but the method of choice is to secure the trusses with metal strapping and then nail them into place on the plate. Another possibility is ventilation channels, for built-in ventilation, built up through the cockloft, old roof, and new cockloft and out the new roof, then covered with a plastic skylight or automatically opening cover. These channels would serve as ventilation shafts to remove smoke and heat from the interior of the building directly to the outside. This would help occupants trying to escape and firefighters trying to enter the building. The smoke channels would have walls built of double plasterboard to retard lateral fire spread.
The trusses are covered with Vito ¾-inch plywood decking. The roofing material on all but two of the roofs we’ve seen is tar paper with shingles.
The remodeling process places a highly combustible, vertical lumberyard on top of a building that already has firefighting problems associated with the old, flat roof and cockloft. For years, firefighters have known they must ventilate such a building vertically to keep the fire out of the cockloft. Once fire enters there, it can spread rapidly, create a backdraft, and cause structural collapse and the eventual loss of the entire building. The remodeling not only makes it impossible to properly ventilate the cockloft; it adds another, larger cockloft or attic on top of the original one.
Besides that, there’s also a smaller mass of wood, which is more easily ignited, and the trusses are subject to early failure and probable total collapse of the roof structure. Also, the design creates an additional dead load. The building has been neglected for some time, and the deterioration of the flat roof has, in some cases, led to damage of the exterior, load-bearing walls, which in most of the buildings we’re dealing with are made of concrete block. In several buildings, there are indications of water damage to the concrete block and the old roof supports. Add the weakening effects of fire and the weight and pressure of fire streams, and you have a building pushed ever closer to a potential collapse. All these conditions must be noted in the prefire plan.
(Photos by T. David Harlow)
Where does prefire planning really begin? Not in the field after the building or remodeling is completed, but during the initial review of the blueprints. When the building inspectors get the blueprints, the fire department should receive a copy to see that all fire codes are followed—and, when necessary, to encourage features that surpass the codes.
The process of going over code compliance together with building inspectors makes the blueprints readily available for prefire planning. However, the construction of new roofs over old is a new phenomenon for us, and the initial review processes didn’t identify the firefighting problems that might exist, such as access openings too small for firefighters in full protective gear and the impracticality of vertical ventilation. Many of the inherent firefighting problems didn’t present themselves until construction was well under way, if not complete, during field inspections of several buildings by on-duty fire companies. The only recourse is to report these problems so they can be addressed in subsequent projects.
Current fire and building codes don’t specifically address the construction of a new roof over an old one, so the plans review must consider any innovative move possible for strict fire prevention.
Sprinkler systems are obviously the first choice for protection, but the builder usually won’t agree to sprinklers because of their cost. Smoke detectors and rate-of-rise heat indicators are good alternatives.
Compartmentalization of the void by a double plasterboard wall will keep the smoke and fire contained in a specific section of the void. (Most codes require compartmentalization when more than 3,000 square feet of space has been enclosed.) This may give fire crews extra time to vent the new roof before the new trusses are totally involved and make the fire easier to control by reducing the large void to several small sections. It will also add to the structural integrity of the new roof.
The prefire plan for a structure with new and old roofs will require all the typical information—construction type, occupancy, contents, interior layout, utilities, and so on. But more important, it must indicate that the building has two separate roof structures. Identify the cockloft access for the old roof, cockloft access for the new roof, and any other openings.
Also indicate unsealed breaches of the old roof. In many cases, the first cockloft and the old roof have been breached for utilities; sewer, furnace, and other vent pipes; and roof access openings. After the final inspection of the new roof, many of these utilities may have been removed for any number of reasons, but the breach in the old roof isn’t repaired. Others may be left intact on the old roof but disconnected from their source below. The reasoning is that the new roof will cover the openings and the new ceiling will hide them. During prefire planning and fire inspections, we’ve found old air duct covers left in place but disconnected from the system on the old roof. This provided a direct access for fire and smoke into the void between the two roofs from the interior below. The old vents must be removed and the opening properly sealed as required by fire codes. Items such as those mentioned must be reported and repaired promptly, according to local fire code procedures.
(Photos by T. David Harlow)
In an old, two-story hotel, we found the old air-conditioning vents were no longer in use. The vents were open from the interior of the second-floor hallways through the cocklofts, and they dead-ended about a foot above the old roof. To seal these vents from above, the construction crews had taken old rolls of tar paper they found on the roof and stuck them down into the vents. The interior side of the vent still had the cover attached. If fire had broken out of a room into the hallway, it would have had a direct access route into the old cockloft and the new attic. The fire would have vented itself out of the shaft below the new roof’s truss supports.
Extra resources must be called immediately upon finding a working fire in a building where a new roof exists over the old. Every aspect of firefighting will be complicated by the two separate roof structures: Engine crews will be slowed by the heat and smoke build-up in the building, and truck crews will be involved in some type of ventilation.
Roof work is hard physical labor, and in this type of fire building, you may initially question the need to open the roof, since it may provide little, if any, relief for interior operations. (They may have to rely on horizontal ventilation.) But remember that the interior flue pipes, pipe chases, and other openings might ventilate directly into the void between the two roofs from the interior below.
The interior attack crews can’t just spray water up through the hole created by the fire in hopes they can extinguish it. As Dayton District Chief Paul Hemmeter has told me, “Once the fire enters the attic or cockloft, I want the entire ceiling [below] on the floor. The combination of truckies dropping the plaster and the engine crews actively hitting the fire is the only way you are going to control the situation.”
Large streams are a necessity when fighting a fire where there’s a double roof. The combination of fast-burning wood trusses and a tightly enclosed area results in high temperatures and a fastspreading fire. The situation will be even worse if the old roof deck is metal, because the metal will transmit heat into the tar and gravel material. This preheating will produce highly flammable vapors which could lead to a backdraft inside the void between the two roofs. The preheating will also produce a quick-spreading fire once the flames break through the old room. So 250-gpm or larger lines are required for good penetration and effective cooling.
When you’re dealing with a large structure, or one where the fire is in the old cockloft and you can’t reach it from underneath, you can cut holes into the gable ends to give hose streams access. Place hose lines in the openings to control the fire when it begins to burn through the old roof and spreads to the new roof structure. Of course, the new roof must be vented above the burn-through area. Allow the smoke and flames to vent, but use the hose line to protect the trusses around the area where the fire is coming out of the old roof’s cockloft. Fire involving the new trusses and the old tar and gravel roof can be extinguished, but do not spray water into the burn-through area, because that would push the heat and smoke down onto the interior crews.
Do, however, use enough water for complete extinguishment. A small, undetected fire in the cockloft or void space can generate enough heat to grow quickly out of control. We’ve educated our firefighters to shut the nozzle off as soon as they darken down a fire, but these structures are built to burn. Water damage is only a secondary consideration.
Once the fire vents itself, the interior conditions will change rapidly. The smoke will usually rise a couple of feet off the floor, but this will quickly be followed by an increase in the intensity of the flames. As that happens, the interior attack crews will have just a few minutes to make a quick and aggressive attack on the fire. At the same time, the roof may become untenable and the crews working there may have to abandon their positions.
If you don’t quickly knock down the burn-through fire to keep it from spreading horizontally through the new roof structure, there are enough voids for the fire to enter to keep you chasing it for hours. The collapse potential will increase and the strategy will shift to defensive. The battle will end when the fire burns the roof off and destroy the building.
We can and should conduct fire inspections in hopes of preventing this type of fire, develop prefire plans to know the best way to fight one, and learn the layout and inherent fire problems associated with the construction principle. But in the end we must concede the fact that these buildings are built to burn. We must remember that we’re not the ones who placed the vertical lumberyards on top of the old cocklofts, and all we can expect of our personnel is for them to do their best in controlling the situation that faces them.
Ventilation will be tough, if not impossible, short of burn-through. And entry for the engine crews will be hot, difficult, and dangerous. We will rescue what victims there may be in the building and keep our firefighters from getting injured. It’s the best we can do.
