“Built Like a Brick Outhouse” —Or Is It?
FEATURES
BUILDING CONSTRUCTION
We all seem to have an intuitive respect for brick. A person with a good physique is said to be like the title of this article. Perhaps our high regard for the material started when we first heard the terrifying tale of the Three Little Pigs. The Wolf was finally defeated when he tackled the pig who had built his house of brick.
Most fire departments wisely require the first-arriving unit at a working fire to describe the building construction. This practice started over 100 years ago when there were only two types of buildings, brick and wood. Today, however, what appears to be a brick building may not be a brick building at all. As firefighters, we should have a knowledge of the many ways that brick is used in building construction, because structures that look identical from the exterior may have completely different construction—and fatally different fire problems.
Buildings that appear to be made of brick include not only buildings of ordinary construction in which brick carries the compressive load, but buildings constructed of:
- Brick veneer on wood;
- Brick veneer on steel;
- Brick veneer on concrete block;
- Brick veneer on cast concrete bearing walls;
- Brick and block panel walls on steel or concrete framed buildings:
- Wet masonry built brick by brick on concrete floor;
- Brick panels built on the ground and erected as a unit;
- Brick bearing walls of reinforced masonry;
- Decorative interior brick or brick veneer walls supported by floor beams;
- Imitation brick of plastic or vermiculite.
Each of these building types can present special problems to fire suppression forces.
SOLID BRICK BEARING AND NON-BEARING WALLS
Variations of solid brick bearing and non-bearing walls include hollow tile and concrete block substituted, out of sight, for more expensive brick. Formerly, such a wall was tied together by the periodic insertion of a row of headers (the end of the brick showing). These bricks often cracked. Today, wire masonry trusses are used and all the bricks are stretchers (the long side of the brick showing). The wall is a composite, that is, the brick and block are expected to act together in resisting the load. Whether such walls are bearing (supporting floor or roof beams, girders, or other structural members) or non-bearing (supporting only their own weight), they are capable of standing by themselves—until a fire breaks out.
Bearing walls are stabilized by the weight of the building; non-bearing walls are not so stabilized and thus more prone to collapse. However, the failure of a bearing wall is more serious in its effect on the structure since it supports other building members.
Collapse of masonry walls
Collapsing masonry walls have killed hundreds of firefighters. Collapse seems almost to be an accepted hazard, and little has been done by fire departments to determine why some walls fall while other, apparently similar ones subjected to equal stress do not.
Since some walls fail and others do not, the commonly stated theory that brick, heated on one side by the fire and cooled on the other side by water, expands unequally and thus collapses is, at the very least, open to question. (This is a polite way of saying that I consider it a myth.)
The basic reason why some masonry walls collapse and others do not is that masonry walls, of similar appearance, are not all equal in their resistance to fire-induced stresses.
Sand lime mortar was used exclusively as a bonding agent until the 1880s when portland cement mortar was invented. For many years thereafter, sand lime mortar continued to be used alone or mixed with portland cement mortar. An expert in moving old buildings describes such structures that are held together with lime mortar as “just a pile of bricks.” Sand lime mortar is water soluble, and a number of non-fire collapses have occurred when water leaks washed sand lime mortar out of the wall. Firefighters should be aware of the fact that to get rehabilitation tax credits, sand lime must be used in repairing old sand lime mortar buildings.
A probationary firefighter, who had heard me lecture on the subject, noted and reported the washout of sand lime mortar from the walls of a structure. The building was cleared and it collapsed shortly thereafter.
Wooden beams carry an amazing amount of masonry load. The destruction or failure of the wood causes the failure of the otherwise impressive masonry structure. Although this must be the cause of many collapses, I have never seen it cited. This deadly construction is not apparent from the exterior. It can only be detected by competent pre-fire evaluations that focus on collapse potential.
The practice of using wooden lintels in the interior portions of masonry walls while showing substantial masonry arches on the exterior is centuries old. At Carrickon-Suir in Tipperary, Ireland, “Black Tom” Ormond hastily built a palatial house because Queen Elizabeth promised to visit him. (She never did.) The heavy masonry walls are carried over openings on wooden beams, which is cheaper and faster than building full arches.
The stonemasons who built such “quick and dirty” structures migrated to the New World and generously shared their technique. I have seen it across the country. Look at masonry buildings. Check the basement and the attic where the walls are exposed. Is the wall over the openings for doors and windows carried on brick arches or on wood? If wood, expect early failure.
Unprotected steel lintels tightly fitted into the brickwork is another technique used in present day construction. Heat will elongate the steel, displacing brickwork. At higher temperatures, the steel will fail. Where fire rolls out such windows, the lintels should be cooled with hose streams.
Also remember that interior steel such as roof beams will elongate at 1,000°F and push down the walls.
Rotten brick work is not uncommon. In Steven Ross’ CONSTRUCTION DISASTERS (published by McGraw-Hill Inc.), A. B. McMillan (a recognized authority on brick) writes “How to Build Leaky Brick Walls with Good Materials.” This tongue-in-cheek article might also be titled “How to Build a Wall That Will Collapse in a Fire.”
Such articles are not written for fun. They are written because the described time and money saving techniques (which produce a fine looking but inadequate wall) are almost universal.
Level floors are achieved by another ingenious trick that I have never seen written up but have observed across the country in buildings as much as 200 years old. A wooden beam is laid in the brick wall level with the location for the bottom of the floor beams. The floor beams are set on the wooden beam. Presto! A nice level floor without shimming. The hidden danger is that if the wood burns out, a plane of weakness (like the scratch you make to cut glass) is created in the wall.
Have you ever seen a report stating that, “A plane of weakness in the wall, created by the burning out of a wooden floor leveler, was responsible for the fatal collapse”? How much warning do you think such a weakness will give? The warning is in knowledge (preplanning), not in anything you can hear or see on the fireground.
Cross walls are any two intersecting walls that are supposed to brace one another. Often they are of different materials such as brick and stone or different types of brick. Typically, the front wall is brick, the side wall stone. They do not react similarly to weather. The joint pulls apart and there is no bracing.
Braced walls (signalled by stars, plates, channel sections, or other spreaders) are another basic sign of structural distress. In addition, braces made of unprotected structural steel or (worse yet) of steel cable (which undergoes total failure at 800°F) will fail at fire temperatures.
Surface brick, a single thickness of masonry applied like a veneer, is attached with metal ties. In some cases, the ties have been so subject to corrosion that they may not exist. A heavy stream hitting such a wall will spread out under the brick face and tear it off in sheets.
When I started studying building construction, I found two books on construction failures by eminent consulting engineers (CONSTRUCTION FAILURE by J. Feld, published by John Wiley & Sons Inc.; and BUILDING FAILURES by T. McKaig, published by McGrawHill Inc.). It occurred to me that if they could look at the ruins of a collapsed building and determine that warning signs had existed before the collapse occurred, we could do the same. Perhaps then we could erase the terrible phrase “The fatal collapse occurred without warning” from our fire service publications.
KNOW YOUR BUILDINGS— THEY’RE THE ENEMY
Steel or concrete framed buildings are often covered with brick, and their walls are usually a brick and block composite. A wall that is supported on each floor is called a panel wall. If the wall panel extends more than one story, it is called a curtain wall. However, the two terms are often used interchangeably.
When the walls have been constructed of wet masonry (brick by brick) on the concrete floors of the framed building, an excellent inherent fire stop is provided. However, this type of construction is expensive, and many high-rise buildings are constructed with pre-fabricated concrete or imitation concrete panels attached to the floor. In some cases, brick masonry panels have been built on the ground and then hoisted into place. These panels have varying degrees of firestopping effectiveness.
One problem with brick and block composite walls used as panel or curtain walls on concrete framed buildings is that concrete tends to shrink as it ages. Concrete never really stops curing. The brick is inflexible. If proper measures are not taken, the brick will crack and may fall off, at times in huge sheets. Loose brickwork is held back in place by channel steel members tied across the building with cold drawn steel cables, which totally fail at
The structural defects cited above are but a few of the many warning signs that can be observed in preplanning. Although this takes time and effort, once the information is entered into the system, it needs little attention, as the defects are permanent. The building may be “modernized,” but the defects will remain—and may even be enhanced. 800°F. Often, no effort is even made to protect the steel cables from fire. Heat from fire will slacken the cables thus permitting the braced brick to fall. Have you ever heard of a report listing “loose brick” as the collapse cause?
Brick veneer walls
Brick masonry panel walls are often used on steel framed structures such as churches and industrial buildings which are usually one story, but of great height. The steel frame supports the roof and the balcony, if there is one. The masonry walls are non-bearing walls and are usually tied to the steel frame for wind resistance. One church I examined is probably typical. The wooden roof is supported by steel trusses. A fire involving the roof would elongate the steel trusses (a 100-foot steel member is nine inches longer at 1,000°F), pushing the columns out of line and possibly pushing down the walls.
Reinforced brick masonry
The height of conventional brick masonry structures is limited to about seven stories. Reinforced brick (or block) masonry combines brick (or block) and concrete so that structures as high as 22 stories have been built with no wall thicker than 12 inches. This type of construction can be used for apartment houses or motels which have a need for many interior walls. It would not be used for an office building because of the need for clear space.
Two wythes (a vertical line of masonry one unit thick) of brick are erected one brick space apart. Reinforcing rods are placed in the void which is then filled with concrete. In construction terms, the brick becomes a “left in place form.” The building is, in effect, a group of masonry boxes tied together, given added strength by the floors they support.
Photos by Frank Brannigan
Such a building would have good firestopping. Since the interior walls are probably reinforced masonry, it will not be possible to go from one apartment to another or bypass a stubborn door by breaking through a gypsum board wall.
Many buildings constructed of other materials are covered with brick facing, often deceiving the observer—which includes many firefighters.
The brick face is one brick thick, and although the wall is supposed to be attached to the basic building, often the quality of the tie system is dubious. Brick veneer can be applied to wood, concrete block (NOTE: this is not the same as brick and block composite walls as described above), steel, concrete, or any other building material.
Brick veneer walls are hazardous and demand very special attention. Just as with brick and block composite walls used on concrete framed buildings, brick veneer used on concrete bearing walls has the problem of the concrete shrinking more than the brick. If this shrinkage is not compensated for, the brick veneer can fall off. Veneer walls are inherently unstable and therefore dangerous.
If the walls or interior of a brick veneered building are heavily involved in fire, stand well clear. An interior collapse or a failure of the structural wall can bring down the veneer. Although this is not a structural collapse, the fact remains that bricks from a veneer wall can do just as much damage to your skull as can bricks from a solid wall. An old house in New York was “improved” by brick veneer—an interior collapse brought down the wall. A fire lieutenant lost his life pushing a probationary firefighter out of harm’s way.
In addition to being added to existing structures to “rehabilitate” the building, brick veneer can be applied as an original construction material. Many buildings are partially brick veneer and partially solid masonry. The variations are endless. The building may be solid masonry only up to a certain floor. Some walls may be solid, others veneer. You cannot tell them apart. Because of the use of the masonry trusses, the solid masonry walls are laid all stretchers just like the veneer wall.
Sometimes, a cast concrete imitation stone is used to improve old frame buildings. This material presents the same hazard as brick veneer, coming away from the structural walls and causing collapse.
I recently looked at what appears to be a six-story brick building. In reality, it is two three-story, wood frame, brick veneered buildings on top of each other. The upper building rests on a reinforced concrete platform. All the floors are wood trusses. The building, which is still under construction, will have a residential sprinkler system. Such a system will do the job if the fire is in the contents. However, if the fire starts in or penetrates the truss void (or trussloft), collapse should be expected. Brick veneer may fall from as high up as six stories.
A brick veneer wall, located in the lobby of a one-story and basement, non-combustible building, had its supporting steel beam heated by a basement fire. The beam attempted to elongate, but because it was restrained by the veneer, it dumped the wall across the corridor.
Imitation masonry
There are various imitation bricks and stone used for interior decoration. Some are of vermiculite, which is noncombustible. Others may be of combustible glass fiber reinforced polyester resin plastic, which you might call fiberglass. Both of these materials are listed in N. Irving Sax’s DANGEROUS PROPERTIES OF INDUSTRIAL MATERIALS, and warnings against inhalation are noted.
CONCLUSION
There is a real danger in assuming that what appears to be a sound, solid brick wall is. And there are no real answers to this problem. Again, pre-plan, know your buildings, and adopt a fire department policy that substitutes informed acceptance of only absolutely necessary risks for macho madness.
Did you ever see a builder at a fire department funeral?
