COLLAPSE AND FIRE EXTENSION IN WOOD-FRAME CONSTRUCTION

BY BILL GUSTIN

The construction of a fire building is one of the most important considerations in a size-up. Fire officers must determine the type of construction early in an incident if they are to know a building’s potential for collapse and spreading fire in concealed spaces. Knowing a building’s construction is also critical in devising an appropriate strategy, initiating effective tactics, and determining how long firefighters can safely operate in the building when its structural members are under attack from fire.


(1) West Palm Beach, Florida, firefighters begin to attack a fire in an old balloon-fram residence. Fire has already extended vertically through nonfirestopped walls and is taking possession of the attack. (Photos by Lazaro Acosta unless otherwise noted.)

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BRICK OR FRAME? OLD OR NEW?

Determining the age and construction of a fire building is vital, but it can be difficult. It has been said that you can’t judge a book by its cover. This is definitely true when applied to construction. Renovations and facades can make an old building look new. What’s more deceiving, however, are new buildings built with dangerously lightweight truss components that are made to look like older buildings constructed with large-dimension lumber.


An old home in a historical district was gutted of its conventional construction and renovated with lightweight trusses.

This is a common practice in historical districts where new structures must appear to be old to maintain the historic character of the neighborhood. In one city in South Florida, old stately homes are completely “gutted” of their heavy, conventional construction and their roof and floors are renovated with lightweight trusses. A city ordinance requires that these houses look exactly the same as they did before renovation. Firefighters in this city are well aware of this practice and do not hesitate to pull ceiling directly inside the front door to check for the presence of trusses when responding to fires in these structures.


When uncertain of a building’s construction, pull ceiling at the front door to check for trusses.

One way to distinguish between a stucco-on-wood frame house and a house with brick or concrete block walls is to look at how deeply the window frames are recessed into the walls. Window frames in frame houses tend to be fairly flush with the exterior walls. Conversely, windows in block or brick walls tend to be recessed four to six inches from the outside surface. This method of distinguishing wood frame from masonry construction is far from foolproof because brick veneer can be dangerously deceptive.


Windows in block or brick houses tend to be recessed.

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Frame houses tend to have windows that are fairly flush with the walls.

There is a vast difference in terms of stability under fire conditions between a true, load-bearing masonry wall and a wood-frame wall covered with brick veneer. Brick and concrete block bearing walls are relatively substantial because they have to support the weight of the building. Brick veneer, on the other hand, is a stack of bricks no wider than the width of a single brick attached to a wall with small metal clips or tabs.


A large portion of this brick veneer collapsed during Hurricane Wilma. Note the small tabs used to tie the veneer to the wood-frame wall.

Brick veneer is inherently unstable because of its height and width. It may be easier to understand this concept if we relate it to your knowledge of technical rescue. In extrication and collapse training, you are taught never to stack cribbing higher than twice the width of its base. To do so would make the cribbing unstable and prone to collapse from a slight lateral shift in the load. Fire attacking the connections to brick veneer can allow it to collapse under its own weight and bury firefighters in a pile of bricks.


A close-up of the metal tabs that connect the veneer to the wall. Fire attacking these connections will allow the inherently unstable veneer to collapse.

In certain areas of the country, it is common to find buildings that have wood-frame and masonry bearing walls, particularly in new residential developments. In South Florida, for example, literally thousands of multi- and single-family homes have a first story built with concrete block and a second story with wood-frame walls. The time to become familiar with these residences is during construction. It is very difficult to tell the difference in construction once the entire structure is covered with stucco or wood siding.

BALLOON-FRAME CONSTRUCTION

From the 1800s to the 1930s-1940s, most wood-frame residences were built with balloon construction. This construction consists of studs (the vertical component of frame walls) that extend from the foundation to the roof line. Floors and rafters are supported by a ledger or “ribbon board” nailed, at right angles, across the studs. Balloon-frame construction creates stud channels-the space bordered by the studs and wall coverings-that are unobstructed from the foundation to the attic. This allows for unimpeded fire spread in the walls. Additionally, balloon framing provides no barrier to stop fire from spreading horizontally between the floor joists. Fire can also follow utilities, such as plumbing and electrical wiring that extend from floor to floor. (This will be discussed later.) To stop unimpeded fire spread, building codes may require balloon-frame homes that undergo extensive renovation to install fire-stops in the walls at specified intervals.


Looking up a stud channel in a balloon-frame house. Fire can spread unimpeded from foundation to attic.

There are ways to identify balloon-frame construction, but the best approach is to assume that any old home is balloon-frame and aggressively pursue any fire that originates or extends to the floors, ceilings, or walls. If not, fire probably will take possession of the entire structure.


The building code requires that this balloon-frame home undergoing renovation have fire-stops installed in the stud channels.

Fire spreading in balloon construction may not be easy to detect when it is concealed by a thick covering of wood or plaster. What begins as a small fire in an electrical outlet on the first floor of an old two-story house can rapidly spread, undetected, to the attic. Firefighters who believe they have isolated the fire to a small area around the electrical outlet on the first floor may be surprised when their chief advises them that smoke is pushing out of the eaves of the roof.

Examine the attic early and often. Smoke in the attic may be the first indication that fire is in the walls, especially if combustible blown-in cellulose is used for insulation. In the case of the electrical receptacle, open the wall and expand the opening until you see clean, unburned wood. Also, remove a baseboard on the second floor directly above the fire, and punch a second examination hole. If possible, minimize property damage by meticulously prying the baseboard so that it can be replaced to cover the hole.


Firefighters cut and pull heavy stucco applied over the original wood siding.(Photos by Mike Conward.)

Fire companies who find smoke pushing from the eaves of an old two- or 2½-story home on arrival have no time to be meticulous. They must be proactive and take decisive action. First, they should assume that it is balloon-frame construction and call for help immediately. Opening walls and pulling ceilings is hard, labor-intensive work. Additionally, firefighters must cover exposures in case the fire “gets away” from them. This is especially important when homes are spaced closely and have asphalt-shingle siding.


Fire in the wall “lights up” as the siding is pulled. (Photos by Mike Conward.)

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(Photo by Mike Conward.)

There are two approaches to stopping fire that is already running the walls in balloon construction. One is from the exterior. This requires cutting and stripping exterior siding-not an easy task. Old balloon-frame homes are commonly covered with thick wood siding or a heavy layer of stucco on wire lath. Additionally, it is not uncommon to find the original siding covered with a brick veneer that was added in later years to change the appearance of the house.

Recently, my company was ordered to open the walls from the exterior of an old-frame house. At first, our plan was to break through the thick stucco with a maul. Our plan changed, however, when we encountered 1-inch × 6-inch wood siding behind the stucco. At that point, we chose a rotary saw to cut through both layers of siding. Powerful saws with carbide teeth or diamond blades definitely have made cutting much easier than swinging an ax. But, you have to pull and strip away building materials after they have been cut. This still must be done the “old-fashioned” way-hard, physical work with hand tools.

The other approach to accessing fire in balloon construction is to pull ceilings and open walls from inside the structure. This is usually easier than opening walls from the exterior because wood lath and plaster are easier to penetrate and pull than exterior siding. This is not to suggest that pulling ceilings and opening walls is a job for lightweights. For example, many old balloon-frame homes were not built with plaster ceilings. Instead, you may encounter a wood ceiling consisting of boards nailed to the underside of the floor joists and rafters. Getting through this ceiling can be a real challenge. (See “Wood Ceilings and Progress Reports.”)

Expect more than one ceiling. Old homes built before air-conditioning typically had high ceilings. In later years, it was quite common to hang a second ceiling below the original ceiling to conceal air-conditioning equipment and ductwork. Water leaks over the years may have damaged the original wood-lath-and-plaster ceiling to a point where it was removed and replaced with a ceiling of plaster on wire lath. Pulling a substantial wire-lath-and-plaster ceiling requires considerable strength and stamina.

When fire is in possession of a balloon-frame home, firefighters must be assigned to open ceilings and walls on every floor. Begin by pulling the ceiling in a strip along the walls. There, a hose stream directed into the opening will run down the open stud channels and extinguish fire spreading up the walls.


A valve connected one hose length back from the piercing nozzle allows mobility.(Photo by Fernando Gomez.)

A piercing nozzle can be very effective in reaching and extinguishing fires in walls and ceilings. They may be especially valuable when there are limited personnel who are becoming exhausted. When using a piercing nozzle, it’s a good idea to connect the control valve one hose length behind the nozzle. This allows firefighters greater mobility and places less strain on the couplings and valve when striking the piercing nozzle with an ax or a maul.


A piercing nozzle driven into the wall. This nozzle is very useful for penetrating thick stucco and wood and in extinguishing fire in concealed spaces.(Photo by Fernando Gomez.)

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The piercing nozzle penetrates ceiling and floods the void space overhead. (Photo by Fernando Gomez.)

Note that the two approaches to accessing fire spreading in a balloon-frame structure are not exclusive of each other. A working fire in a balloon-frame house requires a large commitment of firefighters operating inside and from the exterior. Unfortunately, many fire departments today lack the personnel to cover all positions and perform other vital functions such as roof ventilation.

Experienced fire officers and textbooks on firefighting tactics stress the importance of venting the roof of balloon-frame structures. This is necessary because fire in the walls will ultimately spread to the attic. There, fire will involve roof structural members, and smoke and heat will “mushroom” downward. Vertical ventilation , therefore, will greatly improve conditions in the attic and on the top floor. Many rural and suburban fire departments, however, lack the staffing to perform “timely” roof ventilation-that is, during the initial stages of the operation and before fire has compromised the roof’s stability. When personnel are limited, they probably will be more effective opening walls and pulling ceilings than cutting a hole in the roof-definitely not an ideal situation. If the roof cannot be opened, it is critical to raise ladders to top-floor windows. They may have to be used as an emergency means of egress for firefighters should conditions get “ugly.”

CONTRASTING THE “OLD” WITH THE “NEW”

Builders in the 1920s didn’t use a computer to figure out the smallest and cheapest structural elements to use to build a house. Structural members in older homes generally were larger than they had to be. To illustrate that point, look at the beating old construction can take in a fire and still remain standing. Old, conventional construction used structural members that are considered massive when compared with today’s lightweight truss construction. Older homes have roof rafters no smaller than 2 inches × 6 inches, and floor joists measuring at least 2 inches × 10 inches are the norm.

Floors in old homes commonly consist of 1-inch-thick × 6-inch-wide subfloor decking, often laid diagonally to the floor joists, and a hardwood-finish floor. Roof decking is almost as substantial, commonly using ¾-inch-thick × 4-inch-wide tongue-and-groove boards. Old, conventional construction can withstand fire attacking its structural members and still support the weight of firefighters. It is impossible, however, to give an exact amount of time that firefighters can remain inside or on the roof because there are too many variables that can affect the time to collapse-for example, is the fire accelerated by a flammable liquid or gas? Have portions of the house been renovated with lightweight truss components? Also, who knows exactly how long the fire was burning before firefighters arrived on the scene?

Consider also that old single-family homes and multiple dwellings may have kitchen and bathroom floors that are dangerously overloaded with terrazzo or tile that will hasten collapse. Additionally, an examination of bathroom floors in old homes will often reveal a significant amount of rotten wood from decades of leaky pipes and overflowing toilets. Now consider that old sinks, bathtubs, and toilets amount to a significant dead load in a relatively small, concentrated area. Firefighters assigned to overhaul bathrooms should first examine the floor below for rotten or fire-damaged wood.

PLATFORM-FRAME CONSTRUCTION

After the 1940s, wood homes were rarely built with balloon-frame construction. Since then, “modern” wood homes are commonly built with platform-frame construction. In this type of construction, walls are built in sections consisting of a top plate, a bottom plate, and studs that are only as high as the underside of the floor above. This wall assembly or “platform” rests on the floor with the bottom plate as a base.


In platform-frame construction, the top and bottom plates act as inherent fire-stops. This building, damaged in a hurricane, has both plywood and fiberboard exterior sheathing and the remains of a brick veneer that collapsed.

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Utilities, such as wiring, violate the top plate’s ability to stop vertical extension.

The top and bottom plates in a platform-frame wall act as inherent fire-stops that prevent fire in the wall from spreading from floor to floor-that is, until the plumber, electrician, and sheet metal worker install their utilities inside the walls. Floors and plates must be cut to allow pipes, wiring, and ductwork to extend from floor to floor. Consequently, fire that originates in or extends into the walls can follow the utilities and ultimately spread to the attic.


Fire in the electrical panel on the first floor followed the wiring to the second floor and the attic.

A fire that begins in an electrical panel is a perfect example of how fire can spread in platform-frame construction. The top and bottom plates of the stud channel containing the electrical panel must be penetrated or removed entirely to allow electrical wiring to reach all levels and areas of the house. After securing the electricity, firefighters should open the wall above the panel. If they find fire, they should stop opening the wall and immediately pull the ceiling. Also, firefighters must get to the floor above and pull a baseboard for an examination hole in the wall directly above the panel. Again, check the attic early and often. A thermal imaging camera will be extremely valuable if the attic is filled with smoke.


Note the “critter” driven from its home inside the wall.

When there is fire in a wall, firefighters cannot focus all of their attention on its upward spread. Sparks, hot embers, and melted, burning wire insulation can spread fire below its area of origin. You must look for this before you leave the scene.


Fire followed the plumbing stack to the upper-floor apartments.

Plumbing, particularly sewage piping, can spread fire throughout a structure. For example, a basement fire has the potential to spread, through the plumbing, to every kitchen and bathroom. And, since plumbing stacks penetrate the roof, fire will eventually spread to the attic.


Bathrooms arranged back-to-back in this apartment building share a common plumbing stack, which allowed fire to spread to adjacent apartments.

Modern multiple dwellings, called garden apartments, are notorious for spreading fire in voids that conceal the plumbing. To save money, kitchens and bathrooms of garden apartments are often built back-to-back to share the same plumbing stack. Hence, several apartments can be interconnected by the same plumbing void space.


Fire entering the soffit above these kitchen cabinets can spread fire to adjacent apartments in the void concealing plumbing.

What begins as a grease fire on a stove can quickly spread to the kitchen cabinets and burn through the soffit-the space between the top of the kitchen cabinets and the ceiling. Once fire enters the soffit, it has free access to the plumbing void space and can spread to several apartments.


In any fire involving a basement, kitchen, or bathroom, conduct a thorough examination for fire extension along the plumbing.

Fire spread involving plumbing is worse in new or renovated homes fitted with plastic pipe. This can hasten fire spread because the plastic pipe melts, burns, and contributes fuel to the fire.


Plastic plumbing enhances fire spread-the plastic melts and contributes fuel to the fire.

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LIGHTWEIGHT TRUSS CONSTRUCTION

Large-dimension lumber, such as a 2-inch × 10-inch floor joist, derives its strength from its mass. Lightweight prefabricated trusses, on the other hand, derive their strength from engineering. Lightweight trusses and wood I-beams are designed by computer to carry their intended load with a minimum of building material. That’s good for the firefighter building a home because he would not be able to afford the cost of a home built with large-dimension lumber today. It’s bad for the firefighter crawling across a floor supported with wood trusses when a fire is raging in the basement.


Wood I-beams provide plenty of surface to fuel a fire but very little mass to resist it. “Engineered” components such as wood I-beams and floor trusses can collapse in less than 10 minutes of fire exposure.

Lightweight roof and floor trusses and wood I-beams are strong and help to keep housing affordable. Wood I-beams are actually advertised for their feature of making floors “silent”-they don’t make a creaking sound when walked on. The open-web design of floor trusses is excellent for running plumbing, wiring, and ductwork in the space between the ceiling and the floor above.

Lightweight prefabricated trusses and wood I-beams are truly marvels of engineering except for one fundamental flaw-their horrible performance when involved in fire. As noted, wood trusses and I-beams provide plenty of surface to fuel a fire but very little mass to resist it.

ADAPT TACTICS AND STRATEGY

Laboratory tests and more than 30 years of fire experience should have taught firefighters that lightweight trusses and wood I-beams can collapse in less than 10 minutes. All firefighters should know that they cannot possibly operate under heavy fire conditions in a building constructed with lightweight trusses with the same aggression and for the same amount of time as they would in a building constructed with conventional floor joists and roof rafters. Because of the danger of early collapse, firefighters must determine that truss construction is present at the onset of firefighting operations and adapt their strategy and tactics accordingly.

In a truss, every component depends on other components to carry the designed load, and a truss is only as strong as its weakest component. That “weak link” in a truss is the gusset plate. A gusset plate is a piece of galvanized sheet metal that is run through a stamping machine to form pointed teeth that embed into the surface of a truss to connect its components. The teeth of a gusset plate penetrate the wood 3/8 inch. When exposed to fire, heat conducted through the metal of the gusset plate causes the wood in contact with the teeth to thermally decompose and lose adhesion with the gusset plate.


The teeth of the gusset plate penetrate 3⁄8 inch into the surface of the wood truss member.

Careless workers may compromise the connection of gusset plates to the trusses. Watch when trusses are delivered to a construction site. It is far from a delicate operation. Often, trusses are shoved off a truck and crash to the ground, and gusset plates are loosened or completely detached.


The open web of a floor truss allows wiring, ductwork, and plumbing to pass through the truss. This design allows the fire to take the same unobstructed path and to spread throughout the entire ceiling space.

The open-web design of floor trusses that allows wiring, plumbing, and ductwork to run through the trusses also allows fire to take the same unobstructed path. With conventional floor joists, a fire that starts in a recessed ceiling light fixture will be confined, at least initially, to one joist channel or bay-the space bordered by floor joists at each side, the floor above, and the ceiling below.


The wood floor trusses collapsed shortly after the arrival of firefighters. Firefighters should not be on or under truss construction when it is heavily involved in fire.

Floor trusses, by comparison, provide no inherent lateral fire barrier. A fire that starts in a light fixture can spread unimpeded throughout the entire ceiling space.

The best opportunity to look for trusses is when a building is under construction, before structural members are concealed by plasterboard. It’s a sure bet that any house built in the past 30 years will have a truss roof and possibly truss floors. And remember that old homes can be renovated with lightweight trusses.


Heavy roof tile hastens the collapse of a lightweight wood-truss roof.

To confirm the presence of trusses, open the ceiling immediately inside the door you enter. Say, for example, that you arrive to find an intensive fire in the basement of a two-story home in a new housing development. Family members meet you in the front yard and assure you that everyone is out of the house. As the hoseline is readied at the front door, a ladder company firefighter takes one step inside and pulls down a small section of the vaulted ceiling with a 10-foot pike pole. Then, with a thermal imaging camera, floor trusses or wood I-beams are seen supporting the second floor. The confirmation that trusses are in this house and that all family members are accounted for calls for a change in strategy. Instead of initiating an aggressive interior attack, the first hoseline should be repositioned to the rear of the house and directed into the basement windows or through an outside basement entrance.


Fire destroyed the integrity of the roof trusses and completely burned through the one-half-inch plywood sheathing, leaving the tar paper exposed.

If you suspect fire in an attic, again, pull the ceiling immediately inside the front door. This is critical in modern residential construction where lightweight truss roofs can be covered with thin sheets of plywood or oriented strand board (OSB), sheets made of wood chips glued and pressed together. OSB is a common substitute for plywood. In the Sunbelt, it is not unusual to find roof decking as thin as one-half inch. The danger of roof collapse is compounded when it is covered with, literally, a ton of concrete or clay tile. It is not unusual for roof trusses to sustain heavy fire damage and for the fire to completely burn the roof deck, leaving the roof tiles intact but dangerously unsupported (photos 30-31). This is not a roof firefighters should be on or under.


The heavy roof tile remains intact but is dangerously unsupported.

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Building construction is one of the most important subjects in fire academy basic training but, sadly, this subject is often neglected because of the competing demands for training as the fire service expands its range of services. New firefighters who receive several hours of emergency medical training can identify every organ and bone in the body. On the other hand, many of these firefighters cannot name the most basic components of building construction. This is dangerous. This is not to say that emergency medical training isn’t important; extensive medical training helps firefighters save lives. But, firefighters seldom die on medical calls. They do, however, continue to be killed by building collapse.

Firefighters must be familiar with the types of construction in their area and must continue to learn about new construction methods and building materials throughout their careers.

This article is dedicated to the memory of Francis L. Brannigan, who inspired me and generations of firefighters to become students of building construction. His teachings have undoubtedly saved the lives of many firefighters.

WOOD CEILINGS AND PROGRESS REPORTS

Breaking through and pulling down an old wood ceiling require a strong and determined firefighter using the proper methods and techniques. The key is to make the initial penetration by driving the head of a pike pole parallel to the boards. This allows the hook to split the boards along the grain of the wood. In smoke, you can determine the direction of ceiling boards with a thermal imaging camera, by feeling the texture of the boards by scraping a pike pole across the ceiling’s surface, or by stepping outside and taking a look at the roof. Consider that most wood ceilings, particularly in smaller homes, are nailed at right angles to the underside of the floor joists and roof rafters and that joists and rafters run at right angles to the roof’s ridge line. If that is the case, the ceiling boards will run in the same direction as the ridge line of the roof.


The firefighter prepares to pull the wood ceiling. He positions the pike pole parallel to the ceiling boards with the hook on the floor, to achieve maximum force. (Photos by Kevin Lewis.)

To penetrate an old wood ceiling, thrust your pike pole upward with tremendous force. Begin by holding the pike pole parallel to the ceiling boards with the hook on the floor. This allows the hook to gain momentum before it impacts the ceiling. If the first two thrusts meet solid resistance, it’s probably because the hook is striking the ceiling directly below a joist or rafter. If this occurs, move forward or backward a few inches and try again. Once the ceiling is penetrated, turn 90° so that the hook gains a purchase on the ceiling boards. Now, pull the ceiling alongside a joist or rafter.


The hook makes its initial penetration by breaking between boards or splitting wood along its grain.

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The hook is turned 90° to gain purchase for pulling ceiling boards.

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Report Difficulties and Delays

While on the subject of tough, punishing tasks, I know many officers, particularly new ones, who are reluctant to report a true assessment of their progress to the chief. I have been guilty of this. Several years ago, my company was assigned to pull the ceiling in a store within a strip shopping center. The chief’s strategy was to cut off the spread of fire in the cockloft, and he was depending on my company to get the ceiling down. Although we experienced tremendous difficulty, I never reported our lack of progress to the chief until we were completely exhausted and could no longer perform our task. Had I informed the chief at our first indication of difficulty, he may have changed tactics or assigned additional resources. Perhaps it is ego or embarrassment that makes officers reluctant to report their lack of progress. Officers, however, must be as candid and as timely in reporting failure as they are in reporting success.

BILL GUSTIN, a 33-year veteran of the fire service, is a captain with Miami-Dade (FL) Fire Rescue and lead instructor in his department’s officer training program. He began his fire service career in the Chicago area and teaches fire training programs in Florida and other states. He is a marine firefighting instructor and has taught fire tactics to ship crews and firefighters in Caribbean countries. He also teaches forcible entry tactics to fire departments and SWAT teams of local and federal law enforcement agencies. Gustin is an editorial advisory board member of Fire Engineering.

(1) The firefighter prepares to pull the wood ceiling. He positions the pike pole parallel to the ceiling boards with the hook on the floor, to achieve maximum force. (Photos by Kevin Lewis.) (2) The hook makes its initial penetration by breaking between boards or splitting wood along its grain. (3) The hook is turned 90° to gain purchase for pulling ceiling boards.

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