Building Construction 65

INTRODUCTIONFrom a safety standpoint, all firefighters should

have a basic knowledge of the principles of buildingconstruction. Knowledge of the various types ofbuilding construction and how fires react in eachtype give the firefighter and fire officer an edge inplanning for a safe and effective fire attack. Historyhas shown that failure to recognize the potentialdangers presented by a particular type of construc-tion and the effects a fire has on it can lead to deadlyresults.

New technologies and designs are being usedfor building construction every day. Therefore, itis impossible to highlight every conceivable situ-ation in this chapter. The purpose of this chapteris to introduce the firefighter to some of the mostbasic and common types of building constructionand their fire protection characteristics. The chap-ter will also introduce the firefighter to commonbuilding construction terms and components.This chapter also discusses some of the indica-tors that signify danger during fire fighting op-erations.

TYPES OF BUILDING CONSTRUCTION[NFPA 1001: 3-3.11(a)]

Each of the model building codes classifiesbuilding construction in different terms. In gen-eral, construction classifications are based onthe type of materials used in the constructionand on the fire-resistance rating requirements ofcertain structural components. Most buildingcodes have the same five constructionclassifications, but use different terms to namethe classifications. The five types of buildingconstruction include:

Chapter 3

Building Construction

• Type I (fire-resistive) construction

• Type II (noncombustible or limited combus-tible) construction

• Type III (ordinary) construction

• Type IV (heavy timber) construction

• Type V (wood-frame) construction

Type I (Fire-Resistive) ConstructionFire resistance provides structural integrity

during a fire. Fire-resistive construction hasstructural members, including walls, columns,beams, floors, and roofs, made of noncombustibleor limited combustible materials (Figure 3.1).The fire-resistive compartmentation provided bypartitions and floors tends to retard the spread offire through the building. These features allowtime for occupant evacuation and interior firefighting. Because of the limited combustibility ofthe materials of construction, the primary firehazards are the contents of the structure. In a

Figure 3.1 Type I Construction.

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fire-resistive structure, firefighters are able tolaunch an interior attack with greater confidencethan in a building that is not fire resistant. Theability of fire-resistive construction to confine thefire to a certain area can be compromised by open-ings made in partitions and by improperly de-signed and dampered heating and air-conditioningsystems.

Type II (Noncombustible or LimitedCombustible) Construction

Noncombustible or limited combustible con-struction is similar to fire-resistive constructionexcept that the degree of fire resistance is lower.Noncombustible construction has a fire-resistancerating on all parts of the structure (exterior andinterior load-bearing walls and building materi-als). Materials with no fire-resistance ratings, suchas untreated wood, may be used in limited quanti-ties (Figure 3.2). Again, one of the primary fireprotection concerns is the contents of the building.The heat buildup from a fire in the building cancause structural supports to fail. Another potentialproblem is the type of roof on the building. Noncom-bustible or limited combustible construction build-ings often have flat, built-up roofs. These roofscontain combustible felt, insulation, and roofingtar (Figure 3.3). Fire extension to the roof caneventually cause the entire roof to become involvedand fail.

Type III (Ordinary) ConstructionOrdinary construction features exterior walls

and structural members constructed of noncom-

bustible or limited combustible materials. Inte-rior structural members, including walls, col-umns, beams, floors, and roofs, are completely orpartially constructed of wood (Figure 3.4). Thewood used in these members is of smaller dimen-sions than that required for heavy timber con-struction. See the Type IV (Heavy Timber) Con-struction section that follows. The primary fireconcern specific to ordinary construction is theproblem of fire and smoke spreading throughconcealed spaces. These spaces are between thewalls, floors, and ceiling. Heat from a fire may beconducted to these concealed spaces through

Figure 3.3 The components of a built-up roof.

Figure 3.2 Type II Construction. Figure 3.4 Type III Construction.

Building Construction 67

finish materials, such as drywall, gypsum board,or plaster, or the heat can enter the concealedspaces through holes in the finish materials.From there, the heat, smoke, and gases mayspread to other parts of the structure. If enoughheat is present, the fire may actually burn withinthe concealed spaces and feed on the combustibleconstruction materials in the space. These haz-ards can be reduced considerably by placing fire-stops inside these spaces to limit the spread ofthe combustion by-products (heat, smoke, etc.).

Type IV (Heavy Timber) ConstructionHeavy timber construction features exterior

and interior walls and their associated structuralmembers made of noncombustible or limited com-bustible materials. Other interior structural mem-bers, including beams, columns, arches, floors, androofs, are made of solid or laminated wood with noconcealed spaces (Figure 3.5). This wood musthave dimensions large enough to be consideredheavy timber. These dimensions vary dependingon the particular code being used.

Heavy timber construction was used exten-sively in old factories, mills, and warehouses. It israrely used today in new construction, other thanoccasionally in churches. The primary fire hazardassociated with heavy timber construction is themassive amount of combustible contents presentedby the structural timbers in addition to the con-tents of the building. Though the heavy timbersremain stable for a long period under fire condi-tions, they give off tremendous amounts of heatand pose serious exposure protection problems forfirefighters.

Type V (Wood-Frame) ConstructionWood-frame construction has exterior walls,

bearing walls, floors, roofs, and supports madecompletely or partially of wood or other approvedmaterials of smaller dimensions than those usedfor heavy timber construction. Wood-frame con-struction is the type commonly used to constructthe typical single-family residence. This type ofconstruction presents almost unlimited potentialfor fire extension within the building of origin andto nearby structures, particularly if the nearbystructures are also wood-frame construction (Fig-ure 3.6). Firefighters must be alert for fire comingfrom doors or windows extending to the exterior ofthe structure.

Figure 3.5 Type IV Construction. Courtesy of Keith Flood.

Figure 3.6 Type V Construction.

EFFECTS OF FIRE ON COMMON BUILDINGMATERIALS[NFPA 1001: 3-3.11(a); 4-3.2(a)(b)]

All materials react differently when exposed toheat or fire. Knowledge of how these materials

68 ESSENTIALS

react gives fire suppression personnel an idea ofwhat to expect during fire fighting operations at aparticular occupancy. This part of the chapterreviews the common materials found in buildingconstruction and explains how they react to fireinvolvement.

WoodWood is used in various structural support

systems. It may be used in load-bearing walls(those that support structural weight) or nonload-bearing walls (those that do not support structuralweight). Most exterior walls are load-bearing walls.A party wall that supports two adjacent structuresis a load-bearing wall (Figure 3.7). A partition wallthat simply divides two areas within a structure isan example of a nonload-bearing wall (Figure 3.8).Some interior walls may also be load bearing,although this is often difficult to tell by just lookingat them. This information should be obtained dur-ing pre-incident planning trips.

The reaction of wood to fire conditions dependsmainly on two factors: the size of the wood and themoisture content of the wood. The smaller the woodsize, the more likely it is to lose structural integ-rity. Large pieces of wood, such as those used inheavy timber construction, retain much of theiroriginal structural integrity, even after extensivefire exposure. Smaller pieces of wood can be pro-

tected by drywall or gypsum to increase theirresistance to heat or fire.

The moisture content of the wood affects therate at which it burns. Wood with a high mois-ture content (sometimes referred to as greenwood) does not burn as fast as wood that has beencured or dried. In some cases, fire retardantsmay be added to wood to reduce the speed atwhich it ignites or burns. However, fire retar-dants are not always totally effective in reducingfire spread.

Water used during extinguishing operationsdoes not have a substantial negative effect on thestructural strength of wood construction materi-als. Applying water to burning wood minimizesdamage by stopping the charring process, whichreduces wood’s strength. Firefighters should checkwood studs and structural members for charring toascertain their structural integrity.

Newer construction often contains compositebuilding components and materials that are madeof wood fibers, plastics, and other substances joinedby glue or resin binders. Such materials includeplywood, particleboard, fiberboard, and paneling.Some of these products may be highly combustible,can produce significant toxic gases, or can rapidlydeteriorate under fire conditions.Figure 3.7 A diagram of a party wall.

Figure 3.8 Walls that separate offices or rooms are commonly nonload-bearing walls.

Building Construction 69

MasonryMasonry includes bricks, stones, and concrete

masonry products (Figure 3.9). Masonry in a vari-ety of wall types is commonly used for fire wallassemblies, which consist of all the componentsneeded to provide a separating fire wall that meetsthe requirements of a specified fire-resistance rat-ing. The components include the wall structure,doors, windows, and any other opening protectionmeeting the required protection-rating criteria.Fire wall assemblies may be used to separate twoconnected structures and prevent the spread of firefrom one structure to the next. Fire wall assem-blies can also divide large structures into smallerportions and contain a fire to that particular por-tion of the structure. Cantilever walls are free-standing fire walls commonly found on largechurches and shopping centers (Figure 3.10).

Block walls may be load-bearing walls; how-ever, most brick and stone walls are veneer walls,which are decorative and usually attached to theoutside of some type of load-bearing frame struc-ture.

Masonry isminimally affectedby fire and expo-sure to high tem-peratures. Bricksrarely show anysigns of loss of in-tegrity or seriousd e t e r i o r a t i o n .Stones may spallor lose small por-tions of their sur-face when heated.Blocks may crack,but they usuallyretain most of theirstrength and basicstructural stabil-ity. The mortar be-tween the bricks,blocks, and stone may be subject to more deterio-ration and should be checked for signs of weak-ening (Figure 3.11).

Rapid cooling, which can occur when water isused to extinguish fire, may cause bricks, blocks, orstone to spall and crack. This is a common problemwhen water is used to extinguish chimney fluefires. The water causes the flue liner or firebricks tocrack. Masonry products should be inspected forsigns of this damage after extinguishment hasbeen completed.

Cast IronCast iron is rarely used in modern construc-

tion; it typically is found only in older buildings.It was commonly used as an exterior surfacecovering (veneer wall). These large sections werefastened to the masonry on the front of thebuilding. The cast iron stands up well to fire andintense heat situations, but it may crack or shat-ter when rapidly cooled with water. A primaryconcern from a fire fighting standpoint is that thebolts or other connections that hold the cast iron

Figure 3.9 The main types of masonry construction are stone, concretemasonry products, and brick.

Figure 3.10 A cantilever wall.

Figure 3.11 Mortar is used betweenbricks, blocks, or stone.

70 ESSENTIALS

to the building can fail, causing these large,heavy sections of metal to come crashing down.

SteelSteel is the primary material used for struc-

tural support in modern building construction (Fig-ure 3.12). Steel structural members elongate whenheated. A 50-foot (15 m) beam may elongate by asmuch as 4 inches (100 m) when heated from roomtemperature to about 1,000°F (538°C). If the steelis restrained from movement at the ends, it bucklesand fails somewhere in the middle. For all pur-poses, the failure of steel structural members canbe anticipated at temperatures near or above1,000°F (538°C). The temperature at which a specificsteel member fails depends on many variables,including the size of the member, the load it isunder, the composition of the steel, and the geom-etry of the member. For example, a lightweight,open-web truss will fail much quicker than a large,heavy I beam.

ReinforcedConcrete

Reinforced con-crete is concrete thatis internally fortifiedwith steel reinforce-ment bars or mesh(Figure 3.14). Thisgives the material thecompressive strengthof concrete along withthe tensile strength ofsteel. Reinforced con-crete does not performparticularly well un-der fire conditions; itloses strength andspalls. Heating maycause a failure of thebond between the con-crete and the steelr e i n f o r c e m e n t .Firefighters shouldlook for cracks and

Figure 3.12 A typical steel superstructure.

From a fire fighting perspective, firefightersmust be aware of the type of steel members usedin a particular structure. Firefighters also needto determine how long the steel members havebeen exposed to heat; this gives an indication ofwhen the members might fail. Another possibil-ity for firefighters to consider is that elongatingsteel can actually push out load-bearing wallsand cause a collapse (Figure 3.13). Water cancool steel structural members and reduce therisk of failure, which reduces the risk of a struc-tural collapse.

Figure 3.13 As beams expand, they can push a wall outward, forcing acollapse.

Figure 3.14 Reinforcing rods increasestructural integrity.

Building Construction 71

spalls in reinforced concrete surfaces. This is anindication that damage has occurred and thatstrength may be reduced.

GypsumGypsum is an inorganic product from which

plaster and plasterboards are constructed (Fig-ure 3.15). It is unique because it has a high watercontent, and the evaporation of this water re-quires a great deal of heat. The water contentgives gypsum excellent heat-resistant, fire-re-tardant properties. Gypsum is commonly used toprovide insulation to steel and wood structuralmembers that are less adapted to high heatsituations because it breaks down gradually un-der fire conditions. In areas where the gypsumhas failed, the structural members behind it willbe subjected to higher temperatures and couldfail as a result.

Figure 3.15 Gypsum board is used to cover interior walls.

Glass/FiberglassGlass is not typically used for structural sup-

port; it is used in sheet form for doors and win-dows (Figure 3.16). Wire-reinforced glass mayprovide some thermal protection as a separation,but for the most part conventional glass is not aneffective barrier to fire extension. Heated glassmay crack and shatter when it is struck by a coldfire stream.

Fiberglass is typically used for insulation pur-poses. The glass component of fiberglass is not asignificant fuel, but the materials used to bind thefiberglass may be combustible and can be difficultto extinguish.

Figure 3.16 Some structures have large quantities of glass.

FIREFIGHTER HAZARDS RELATED TOBUILDING CONSTRUCTION[NFPA 1001: 3-3.9(a); 3-3.11(a); 4-3.2(a)(b)]

The primary objective of understanding build-ing construction and materials principles is toapply that information to the fireground.Firefighters should use their knowledge of theseprinciples to monitor building conditions for signsof structural instability. Any problems that arenoted should be reported to incident commandpersonnel as quickly as possible. Even though aspecific safety officer may be designated at thescene, it is the obligation of all personnel to con-stantly monitor for unsafe conditions. The follow-ing sections highlight some of the more criticalissues related to building construction that affectfirefighter safety.

Dangerous Building ConditionsFirefighters must be aware of the dangerous

conditions created by a fire, as well as dangerousconditions that may be created by firefighters try-ing to extinguish a fire. A potentially serious situ-ation can be compounded if firefighters fail torecognize the seriousness of the situation and takeactions that only make the situation worse.

There are two primary types of dangerous con-ditions that may be posed by a particular building:

• Conditions that contribute to the spreadand intensity of the fire

• Conditions that make the building suscep-tible to collapse

These two conditions are obviously related —conditions that contribute to the spread and

72 ESSENTIALS

intensity of the fire increase the likelihood of struc-tural collapse. The following sections describe someof these conditions.

FIRE LOADING

Fire load is the maximum heat that can beproduced if all the combustible materials in a givenarea burn. Heavy fire loading is the presence oflarge amounts of combustible materials in an areaof a building. The arrangement of materials in abuilding directly affects fire development and se-verity and must be considered when determiningthe possible duration and intensity of a fire.

Heavy content fire loading is perhaps one of themost critical hazards in commercial and storagefacilities because the fire may quickly override thecapabilities of a fire sprinkler system (if present)and cause access problems for fire fighting person-nel during fire fighting operations (Figure 3.17).Proper inspection and code enforcement proce-dures are the most effective defense against thesehazards.

COMBUSTIBLE FURNISHINGS AND FINISHES

Combustible furnishings and finishes contrib-ute to fire spread and smoke production (Figure3.18). These two elements have been identified asmajor factors in the loss of many lives in fires.Proper inspection and code enforcement proce-dures are the most effective defense against thesehazards.

ROOF COVERINGS

Roof coverings are the final outside layer that isplaced on top of a roof assembly. Common roof

Figure 3.17 Commercial occupancies, such as this tire warehouse, mayhave heavy content fire loading.

Figure 3.18 Furniture stores have considerable amounts of combustiblefurnishings.

coverings include wood and composite shingles,tile, slate, tin, and asphaltic tar paper. The com-bustibility of a roof’s surface is a basic concern tothe fire safety of an entire community. Some of theearliest fire regulations ever imposed in the UnitedStates hundreds of years ago related to combus-tible roof-covering issues because these roof cover-ings caused several conflagrations from flamingembers flying from roof to roof.

History has shown time and time again thatwood shake shingles in particular, even whentreated with fire retardant, can significantly con-tribute to fire spread. This is a particular problemin wildland/urban interface fire situations wherewood shake shingle roofs have contributed to largefires (Figure 3.19). Firefighters must use aggres-sive exposure protection tactics when faced withthis type of fire.

Figure 3.19 Wood shake shingles are major contributors to fire spread.

Building Construction 73

WOODEN FLOORS AND CEILINGS

Combustible structural components such aswood framing, floors, and ceilings also contributeto the fire loading in a building. Prolonged expo-sure to fire may weaken them and increase thechances of collapse.

LARGE, OPEN SPACES

Large, open spaces in buildings contribute tothe spread of fire throughout. Such spaces may befound in warehouses, churches, large atriums, com-mon attics or cocklofts, and theaters (Figure 3.20).In these facilities, proper vertical ventilation (chan-neling smoke from a building at its highest point)is essential for slowing the spread of fire (seeChapter 10, Ventilation).

Figure 3.20 Buildings with large open spaces burn fast, and in manycases, they collapse quickly.

BUILDING COLLAPSE

Many firefighters have been seriously injuredor killed by a structural collapse at fire fightingoperations. The collapse results from damage tothe structural system of the building caused by thefire or by fire fighting operations. Knowledge of thetypes of construction and the ability to recognizethem is important to firefighters. Some buildings,because of their construction and age, are moreinclined to collapse than others. For example, build-ings featuring lightweight or truss constructionwill succumb to the effects of fire much quickerthan a heavy timber building. Older buildings thathave been exposed to weather and have been poorlymaintained are more likely to collapse than newer,well-maintained buildings (Figure 3.21). Woodenstructural components in older structures mayalso dehydrate to the point that their ignitiontemperature decreases and their flame spread char-

acteristics increase. Information on building ageand construction type should be obtained whenconducting inspections and documented in pre-incident plans.

The longer a fire burns in a building, the morelikely it will collapse. Fire weakens the structuralsupport system until it becomes incapable of hold-ing the weight of the building. The time it takes forthis to happen varies with the fire severity, thetype of construction, the presence or absence ofheavy industrial machinery on upper floors or onthe roof, and the general condition of the building.Firefighters should be aware of the following indi-cators of building collapse and be on the lookout forthem at every fire:

• Cracks or separations in walls, floors, ceil-ings, and roof structures (Figure 3.22)

• Evidence of existing structural instabil-ity such as the presence of tie rods andstars that hold walls together (Figure 3.23)

• Loose bricks, blocks, or stones falling frombuildings

• Deteriorated mortar between the masonry

• Walls that appear to be leaning

• Structural members that appear to be dis-torted

• Fires beneath floors that support heavymachinery or other extreme weight loads

• Prolonged fire exposure to the structuralmembers

Figure 3.21 Old buildings can become very dangerous during fires.

74 ESSENTIALS

• Unusual creaks and cracking noises

• Structural members pulling away from walls

• Excessive weight of building contents

Fire fighting operations also increase the riskof building collapse. Improper vertical ventilationtechniques can result in the cutting of structuralsupports that could weaken the structure. Thewater used to extinguish a fire adds extra weight tothe structure and can weaken it. Water only a fewinches (millimeters) deep over a large area can addmany tons (tonnes) of weight to an already weak-ened structure.

Immediate safety precautions must be taken iffire personnel believe that the collapse of a buildingis imminent or even possible. First, all personnelwho are operating within the building should im-mediately evacuate. Second, a collapse zone shouldbe set up around the perimeter of the building(Figure 3.24). The collapse zone should be equal to

Figure 3.22 Firefighters should look for cracks and repaired cracks in thewalls of buildings that may affect structural integrity.

Figure 3.23 Reinforcement stars on a building are an indication that thebuilding was already in bad shape before the fire started.

one and a half times the height of the building. Nopersonnel or apparatus should be allowed to oper-ate in the collapse zone except to place unmannedmaster stream devices (see Chapter 14, Fire Con-trol). Once these devices have been placed, person-nel should immediately retreat to an area outsidethe collapse zone. Firefighters must always beaware of any evacuation or emergency signals usedby their department.

Lightweight and Truss Construction HazardsOne of the most serious building construction

hazards facing firefighters today is the increaseduse of lightweight and trussed support systems(Figure 3.25). Lightweight construction is mostcommonly found in houses, apartments, and smallcommercial buildings. The two most common typesare lightweight metal and lightweight wood trusses.Lightweight steel trusses are made from a long steel

Figure 3.24 A collapse zone should be equal to one and a half times theheight of the building.

Figure 3.25 Lightweight truss construction can be extremely hazardousto firefighters during fire fighting operations.

Building Construction 75

bar that is bent at a 90-degree angle with flat orangular pieces welded to the top and bottom (Fig-ure 3.26). Lightweight wood trusses are constructedof 2- x 3- or 2- x 4-inch boards that are connectedtogether by gusset plates (Figure 3.27). Gussetplates are small metal plates (usually 18 to 22gauge metal) with prongs that penetrate about ³�₄-inch (10 mm) into the wood.

Experience has shown that lightweight metaland wood trusses will fail after 5 to 10 minutes ofexposure to fire. For steel trusses, 1,000°F (538°C)is the critical temperature. Gusset plates in woodtrusses will fail early when exposed to heat. Al-though the trusses may be protected with fire-retardant treatments to give longer protection,most are not protected at all.

Figure 3.26 Unprotected lightweight steel trusses fail quickly whenexposed to high heat.

Figure 3.27 Wood trusses connected together with gusset plates.

Wooden I beams are also used in lightweightconstruction. They have fire characteristics simi-lar to wood trusses and similar precautions shouldbe used when they are found in a structure (Figure3.28).

Other types of trusses, such as bowstrings, arefound in virtually every community. They are usedin buildings that have large open spaces such as cardealerships, bowling alleys, factories, and super-markets. Bowstrings are often easily denoted bytheir rounded appearance, though many appearotherwise (Figure 3.29).

Figure 3.28 Lightweight wooden I beams are made by nailing 2- x 4-inchboards together.

Figure 3.29 The telltale rounded shape of a bowstring truss roof may behidden by square-end parapets.

All trusses are designed to work as an integralunit. Some members are in tension (vertical andhorizontal stresses that tend to pull things apart),and others are in compression (vertical and

76 ESSENTIALS

horizontal stresses that tend to press things to-gether). One thing common to all types of trusses isthat if one member fails, the entire truss is likely tofail. Once an entire truss fails, usually the trussnext to it fails, and the domino principle soon takesover until a total collapse occurs.

It is important that firefighters know whatbuildings in their district have truss roofs or floors.Truss-containing buildings exposed to fire condi-tions for 5 to 10 minutes (which is usually how longthey have been exposed before the fire departmentarrives) should not be entered, and crews shouldnot go onto the roofs.

Construction, Renovation, and DemolitionHazards

The risk of fire rises sharply for a number ofreasons when construction, renovation, or demoli-tion is being performed on a structure. One contrib-uting factor is the additional fire load and ignitionsources (such as open flames from torches andsparks from grinding or cutting processes) broughtby building contractors and their associated equip-ment.

Buildings under construction are subject torapid fire spread when they are partially com-pleted because many of the protective featuressuch as plasterboard are not yet in place (Figure3.30). The exposed wood framing can be likened toa vertical lumberyard. The lack of doors or othermeasures that would normally slow fire spread arealso contributing factors to rapid fire growth.

Buildings that are being renovated, demol-ished, or abandoned are also subject to faster than

normal fire growth. Breached walls, open stair-wells, missing doors, and disabled fire protectionsystems are all potential problems. The potentialfor a sudden building collapse during fire condi-tions is also a serious consideration. Arson is alsoa factor at construction or demolition sites becauseof easy access into the building.

Due to the rising costs of new construction,renovating old buildings is becoming more popu-lar. Hazardous situations may arise during reno-vation construction because occupants and theirbelongings may remain in the building while con-struction continues. Fire detection or alarm sys-tems may be taken out of service or damagedduring renovation. With the accumulation of de-bris, new construction materials, and equipment,exits can easily be blocked if good housekeeping isnot maintained, preventing the egress of personsfrom the building in an emergency.

Figure 3.30 “Skeleton” of a wood building under construction.