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BUILDING CONSTRUCTION

INTRODUCTION

The most important reason for understanding building construction is safety.Firefighters should be able to identify the types of building construction, associatedterminology, and type of roof, to know when it is no longer safe to remain in or onthe building Firefighters must be familiar with the basics of building constructionand how a fire in a particular building can affect its structural integrity Knowingcommon building construction terminology will allow firefighters to understandand interpret building construction experts who may be called to a structure fire.Firefighters must also have an understanding of the major roof types and be aware

of their associated strengths and weaknesses When attacking a fire, this knowledgewill make it easier to avoid serious injury or fatalities due to the hazards intrinsic

to a particular roof type

Buildings may collapse for a variety of reasons including stress, poor construction,

or deterioration Firefighters should be aware of the potential and imminentindicators of building collapse They should be able to inspect a building andidentify those indicators which may lead to building collapse, both under normalconditions and during fire suppression operations These indicators, in some cases,may be avoided or alleviated Firefighters must know what to do under thesecircumstances and when it is no longer safe to remain in, on, or near the building

An example might include the steady build-up of the water level when fighting aninternal structure fire It may be possible to reduce the amount of water on the floor

by either knocking out the lower windows at floor level or by drilling holes in thefloor

Another important aspect of building construction that firefighters must be cerned with is building classifications and the basic differences between each type

signs of potential structural collapse during fire operations.

be noted during an emergency These may include:

hazards of each

safety, which would include:

work for high-rise construction

The following dwelling cutaway, overviews examples of construction terminologyand techniques that are useful in developing a basic knowledge of constructionfundamentals

Definitions of Wall Types

Bearing Wall: A bearing wall is capable of supporting a vertical load, such as a floor

or a roof, in addition to its own weight

Non-bearing Wall: This wall is not designed to support a vertical load

Exterior Wall: An exterior wall separates the interior from the exterior of a building.Such a wall is usually exposed to the outside, though not always It forms the extent

or boundary of the building

Interior Wall: This wall will be wholly within a building and will not be exposed

to weather

Party Wall: A party wall usually separates two buildings of distinct ownership andlies on the lot dividing line between the two properties This wall can be eitherbearing or non-bearing

Fire Wall: This type of wall is erected to prevent the spread of fire It must havesufficient fire resistance to withstand the effects of the most severe fire that couldoccur in the building As well, it must provide a complete barrier to the spread offire Any openings in this type of wall must be properly protected

One-Hour Wall: This is a term often used in the fire service There are 83 differentways to construct a typical one-hour wall as described in Chapter 43, Table 43-A, ofthe Uniform Building Code A typical one-hour wall will be non-bearing and willconsist of either:

• 2"x4" wood studs, 16 inches centered, with both sides covered by one

layer of 5/8" type “X” gypsum wallboard

• 3 1/4" “Tin Can” metal studs, 24 inches centered, with both sides

covered by one layer of 5/8" type “X” gypsum

Partition: This is an interior wall, one story or less in height, which separates twoareas A partition can be either bearing or non-bearing

Fire Partition: This is a partition that will inhibit the spread of fire but does notqualify as a fire wall

Curtain Wall: A curtain wall is an exterior, non-bearing wall more than one story

in height It is usually supported by the structural frame

Panel Wall: This is an exterior wall one story in height In a multistory building,

a building.

Shear Wall: This type of wall is erected to assist in resisting the force of wind It isbuilt within the building and usually is part of some required enclosure, such as anelevator or stair shaft This is a bearing wall

Veneer Wall: This is an exterior wall created to improve the appearance of abuilding It is constructed from a variety of materials including marble, brick, stone,

or steel The most common veneered wall is brick on a wood frame These wallsare unsupported and are only as strong as the underlying wall During a fire, thesewalls can become very unsafe

Basic Roof Types

The following roof types summarize the majority of different types of roofs foundwithin the city of San Diego and surrounding areas There are several others, but ingeneral they are a variation of these types Each type will be covered in detail further

on within this section

Description: “A” frame configuration Conventional or ordinary constructionconsists of a ridge board, rafters from the ridge board down to and across the outsidewalls (studs) Ridge and rafters are usually 2x6 inches or larger Rafters are usually

16 inches to 24 inches “on center” Additional support is provided by collar beamsand ceiling joists The roof is constructed in semi-flat to steep pitches

Strengths: Ridge board, rafters (if 2x6 inches or larger) and the area where rafterscross the outside walls

Hazards: Older gables may use 2x4 inch rafters Newer roofs use 3/8 or 1/2inchplywood as a decking instead of 1x4 inch or 1x6 inch stripping Plywood will burnand fail at a faster rate, offers little resistance to fire, and is difficult to remove forventilation purposes

Description: Similar to gable roof, but no “A” frame configuration Ends of roofterminate in “hip” configuration Conventional or ordinary construction consists ofridge pole (board), hip rafters from the ridge pole down to and across the corners

at the outside walls Valley rafters are utilized where two roof lines are joinedtogether Ridge and rafters are usually 2x6 inches or larger Rafters are usually 16

to 24 inches “on center” Various degrees of pitch are utilized

CORRUGATED ROOF

Description: Fast and inexpensive to erect whether large or small Corrugationsconsist of steel, aluminum, or fiberglass over a wood or metal substructure.Corrugated steel is often utilized, usually 18 to 20 gauge thickness (About thethickness of an American car fender, 0475".)

Strengths: Ridge and area where roof crosses the outside bearing walls

Hazards: Corrugations may be steel, aluminum, or fiberglass Expect rapid failure

of these materials when exposed to heat or fire Some buildings utilize plastic orfiberglass panels in the roof as skylights Personnel should consider this roofextremely hazardous for ventilation operations

Description: Steel or wood substructure covered by corrugated metal “RobertsonDecking”; an air-entrained mixture of sand, cement, and occasionally pea gravel ispumped on top of the corrugated metal decking and wire mesh to a thickness ofabout 3 to 4 inches Composition roofing material is utilized as a final layer.

Strengths: Lightweight concrete surfaces offer a strong, hard surface Structurallysound and resilient to fire

Hazards: Difficult to penetrate with chain-saw or rotary saw with a masonry blade.Use a rotary saw with carbide-tipped wood blade to cut ventilation holes

Strengths: Substructure constructed from adequate (2x8 inch, 2x10 inch, etc.)lumber Easy to ventilate-open the hinged panes of glass Consider the area whererafters cross or are tied into the vertical walls as strong areas.

Hazards: Newer sawtooth roofs are covered with 1/2 inch plywood Plywooddecking provides little resistance to fire

BRIDGE TRUSS ROOF

Description: Wooden truss members constructed from 2x12 inch lumber withsloping ends Usually a heavy grade of construction Metal tie rods may be usedvertically for additional support Joists are 2x6 inch and 2x8 inch and covered with1x6 inch sheathing and composition roofing material

Strengths: Well-constructed Consider the perimeter of the building (where trussesand the roof are anchored to outside bearing wall) and the bridge truss members asstrong areas

Hazards: Dependent on the size of lumber utilized and span of trusses Trusses are

in “tension” and “compression” and will fail under severe fire conditions If metaltie rods are used, early failure of rods will affect the stability of the trusses

BOWSTRING ARCH ROOF Description: Arch roof with tie rods and turnbuckles offering lateral support Tierods with turnbuckles are used below each arch member to support the exterior

walls Tie rods may pass through the exterior wall to an outside plate facilitatingidentification Tension is maintained by turnbuckles Top chords or arch membersmay utilize laminated 2x12’s or larger 2x10 inch rafters are covered by 1x6 inchsheathing and composition roofing material

Strengths: This roof utilizes a good size of lumber and 1x6 inch sheathing as the roofdecking Consider the perimeter of the building and the bowstring arch members

as strong areas

Hazards: The main hazard is early failure of metal tie rods and turnbuckles Tierods (tension) provide lateral support to the walls and keep the arches (compres-sion) from pushing the exterior walls outward, and prevent collapse of the building

RIBBED (TRUSSED) ARCHED ROOF

Description: Usually large size (2x12, 2x14 inch) of wooden members utilized toconstruct truss arch Some arches have multiple laminated beams to form one arch.Rafters (2x10 inch or larger) are covered with 1x6 inch sheathing and compositionroofing material

Strengths: Most roofs of this type are well-constructed Consider the perimeter ofthe building and the trussed arch members as strong areas

LAMELLA ROOF (SUMMERBELL)

Description: Egg-crated, geometric, or diamond-patterned roof This roof iscommonly known as a “Summerbell Roof”, however, it is lamella roof constructiondeveloped by the Summerbell Company Constructed from 2x12 inch woodframing, steel plates, and bolts at junctions of framing Roof decking is 1x6 inchsheathing and composition roofing material Arch roof is supported by exterior

“buttresses”, or internally by tie rods and turnbuckles

Strengths: Good construction utilizing solid construction techniques and lumber.Consider the perimeter of the building as a strong area

Hazards: Possible total roof collapse if fire removes more than 20% of roof structure.Collapse may occur from the “domino effect.”

Description: Wood joists (or rafters) of various sizes laid across the outside walls

or outside walls to interior walls or structural supports Joists may also besuspended by metal hangers Joists are covered with 1x6 inch sheathing or plywoodand composition roofing material Very common roof

Strengths: Dependent on the size of the joists and type of decking utilized.Consider the perimeter of the building as a strong area

Hazards: Degree of hazard presented by joist is based on span, size of joist,

“on-Basic Roof Coverings

During firefighting and roof ventilation procedures there are a number of roofcoverings that will be encountered It is important for firefighters to familiarizethemselves with the different materials used, and the strengths and hazards of each

In this way the proper method of ventilation can be used in an expedient and safemanner

Shake shingles: (Wood and Composite) Wood shingles or shakes are split pieces

of red cedar wood used for roofing or siding They are usually attached to 1x6 inchskip sheeting Newer wooden shakes are now treated with fire retardent Compos-ite or shake substitutes are made to simulate wood shake shingles, but in fact aremade of a variety of non-combustible materials

Strengths: Composite shakes are non-combustible Walking on rafters offers mostsupport

Hazards: Wood shakes are combustible Skip sheeting offers little support whenweighted

Asphalt composition shingles: This shingle consists of a fiberglass mat that isimpregnated with asphalt Plywood is placed over rafters and felt is placed on top

of the plywood Finally, the shingle is stapled or nailed over the felt

Strengths: Walking on the rafters, valley rafters or ridgepole offers the best support.Hazards: This material will melt and burn

Heavy felt: This is asphalt-impregnated felt which comes in rolls A hot mopprocedure of tar is placed over plywood and the felt rolled over it This material isused predominately on flat roofs

Strengths: Walking on joists and over exterior walls

Hazards: This material will melt and burn Since this is typically used on flat roofs,firefighters will encounter lightweight construction methods on more recent homes.Under heavy fire conditions, this type of roof can fail quickly

Tile: These can be made from a variety of materials They consist of:

Strengths: The overlap area offers most support The tiles are non-combustible.

Hazards: Stability of roof is masked Tiles can be extremely slippery when wet.When ventilating, tiles must be removed and can slide off the roof and cause injury.Ridge caps must be removed before a roof ladder can safely be hooked over theridge board If trusses are exposed to fire the roof will collapse rapidly

Metal: Steel roofing is a Class I (non-combustible) lightweight roofing material thatcomes in 4' x 15" panels The roofing panels have the look of tile or can resemble thetraditonal wood shake roof This type of roofing material prevents embers fromigniting roofs during wind-driven fires As building codes in the wildland/urbaninterface become stricter, this type of roofing material has become more prevalent

in California

Steel roofing can be installed directly over an existing wood shake roof This makes

it easy and less expensive to install The panels are placed on a 2' x 2' batten and 1' x 4'counterbatten grid system To strengthen the roof, the panels are staggered likebrick work and nailed horizontally One indication of this type of roofing is theoversized metal trim, of 4' to 6', found on the fascia boards and the end caps Anotherindication is the steel roofing panels will not break when struck by a sledge or axe.Sounding and/or walking on the roof should be done at the bottom of the panelswhere the battens are located Avoid areas that feel hot and sticky underfoot

For more information review training video entitled "Stone-Coated Steel Roofs",available at video library at headquarters

Strengths: Strongest part of roof is at the bottom of the panels where the battens arelocated Panels are non-combustible

Hazards: Two problems have surfaced in four Southern California cities whenfighting fires in structures with steel roofs The first problem is rapid and undetec-ted fire spread under the new roof The method of applying steel roofs over existingcombustible roofs creates a space (approximately 4") between the old and the newroof This 4 inches of hidden space provides an avenue for the fire to spread rapidlyand to move undetected through the entire length of the roof Once the original,combustible roof is burning, the entire new roof must be removed to ensurecomplete extinguishment

LIGHTWEIGHT CONSTRUCTION METHODS

Lightweight building and roof construction is currently very popular with tects and building contractors across the country Considering the present cost oflabor, equipment, and building materials, it is not economically feasible to con-struct buildings the same as 50 years ago Ease of installation and utilization oflightweight building materials have become the standard during the last 25 years.Heavy timber, laminated beams, and 1x6 inch sheeting have been replaced by 2x4’sand1/2 inch plywood regardless of building size New style buildings with theircharacteristic concrete tilt-up walls, false fascias, and flat roofs are other indicationsthat lightweight construction may be present As a result of architects' reducing thesize of what there is to burn, today’s fire departments are losing one of their mostvaluable fireground factors-TIME

archi-This section will focus on the five major types of lightweight roof construction:

NOTE: This type of construction may also be utilized in floors , walls, etc

PANELIZED ROOF SYSTEM

Description: This roof can be found on structures constructed of wood, masonry,

or concrete tilt-up slabs This roof consists of four major components:

4 1/2 or 5/8 inch plywood decking

Panelized roofs do not have a space between the ceiling and underside of the roofoccupied by the familiar trussed joist construction The roof is usually constructed

by laminating beams of various sizes (6x36 inches are common) The beams aresupported at their ends by pilaster or posts and additional posts may be supportingthe beam along the span The beams will be spaced from 12 to 40 feet apart and may

be bolted together to create lengths well in excess of 100 feet

Wooden purlins are installed with metal hangers on 8 foot centers The commonsize of a purlin is 4x12 inches with the length depending on the spacing betweenbeams Joists measuring 2x4 inches x 8 feet are installed with metal hangers on 2 footcenters between the purlins and run parallel to the beams.Sheets of plywood (4 x 8 feet

composition roofing material A three-layer insulation paper is stapled to theunderside of the roof between the beams and purlins This paper offers littleprotection to the 2x4 inch joists and 1/2 inch sheets of plywood Insulation paperconsists of tar- impregnated kraft paper covered on either side by thin aluminumfoil

Strengths: The strengths of this roof are beams, purlins, perimeter of building(where roof ties into the exterior walls)

Hazards: Span supports for beams of 4 inch hollow steel pipe may be found Expectweakening and/or collapse of these supports with failure of large portions of theroof under heavy fire conditions When the insulation paper is subjected to fire, thefoil will peel away from the middle layer of tar-impregnated paper This paper willthen begin to give off flammable gases which build up between the insulation paperand plywood decking

When ignition temperature is reached, the gases will flash resulting in heavy char