THE ENGINEEREDWOOD ASSOCIATION

APA

FIRE-RATED SYSTEMSDESIGN/CONSTRUCTION GUIDE

Wood is the right choice for a host of construction applications. It is theearth’s natural, energy efficient and renewable building material.

Engineered wood is a better use of wood. The miracle in today’s woodproducts is that they make more efficient use of the wood fiber resource to make stronger plywood, oriented strand board, I-joists, glued laminated

timbers, and laminated veneer lumber. That’s good for the environment, and good fordesigners seeking strong, efficient, and striking building design.

A few facts about wood.■ We’re not running out of trees. One-third of the United States land base– 731 million acres – is covered by forests. About two-thirds of that 731million acres is suitable for repeated planting and harvesting of timber. Butonly about half of the land suitable for growing timber is open to logging.Most of that harvestable acreage also is open to other uses, such ascamping, hiking, and hunting. Forests fully cover one-half of Canada’s land mass. Of this forestland, nearly half is considered productive, or capable of producing timber on asustained yield basis. Canada has the highest per capita accumulation of protected naturalareas in the world – areas including national and provincial parks.

■ We’re growing more wood every day. American landowners plant more than two billion trees every year. In addition, millions of trees seednaturally. The forest products industry, which comprises about 15 percentof forestland ownership, is responsible for 41 percent of replanted forestacreage. That works out to more than one billion trees a year, or about

three million trees planted every day. This high rate of replanting accounts for the fact thateach year, 27 percent more timber is grown than is harvested. Canada’s replanting recordshows a fourfold increase in the number of trees planted between 1975 and 1990.

■ Manufacturing wood is energy efficient.Wood products made up 47 percent of allindustrial raw materials manufactured in theUnited States, yet consumed only 4 percentof the energy needed to manufacture allindustrial raw materials, according toa 1987 study.

■ Good news for a healthy planet. For every ton of wood grown, a young forest produces 1.07 tons of oxygen and absorbs 1.47 tons ofcarbon dioxide.

Wood, the miracle material for the environment, for design, and for strong, lasting construction.

NOTICE:The recommendations inthis guide apply only topanels that bear the APAtrademark. Only panelsbearing the APA trademarkare subject to theAssociation’s qualityauditing program.

RATED SHEATHING

EXPOSURE 1SIZED FOR SPACING32/16 15/32 INCH

000PS 1-95 C-D PRP-108

THE ENGINEERED

WOOD ASSOCIATIONAPA

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Percent of Percent ofMaterial Production Energy Use

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Steel 23 48

Aluminum 2 8

CONTENTS

Introduction . . . . . . . . . . . . . . 3

Fireproof vs. firesafe . . . . . . . 4

The basics of fire protection . . 5Safety criteria . . . . . . . . . . . . . . 5Protection methods . . . . . . . . . . 7Meeting the building codes . . . 10Insurance provisions . . . . . . . . 11

How to build for fire protection . . . . . . . . . . .12

Wall systems . . . . . . . . . . . . . .12Floor and roof systems . . . . . . .16APA Rim Board Assemblies

(one- and two-hour) . . . . . . .21Structural glued

laminated timber . . . . . . . . . .21

Appendix . . . . . . . . . . . . . . . .23

Bibliography . . . . . . . . . . . . .26

About APA . . . . . . . . . . . . . . .27

lanning and designing buildings that

provide good fire protection, don’t cost

too much to build or insure, meet the

codes, make the best use of materials,

and strike a balance between form and function

is complicated.

The problem arises from the lack of standardized

code provisions and insurance rating practices,

and partly from the rapid advance of

construction technology itself. Many of these

advances have changed and improved wood

construction’s acceptance by building codes

and insurance rating agencies.

This brochure from APA – The Engineered Wood

Association is designed to bring you up to date

on what are considered today among the most

cost-effective fire-rated construction systems you

can design or build – wood and wood structural

panel systems. It provides hard facts about

what’s available, what’s acceptable, and what’s

best practice. For additional information or

assistance with specific design problems, contact

the nearest APA regional field office listed on the

back cover. A bibliography of other helpful

sources is also provided on page 26.

P

For updated editions of this publi-cation and additional informationon this topic, visit the Association’sweb site at www.apawood.org

4

FIREPROOF

VS. FIRESAFE

The first step of designing or buildingfor fire protection is to recognize thatfireproof buildings simply don’t exist.The contents are the critical factor.Almost any building’s contents willburn, and the smoke and heat thusgenerated can cause extensive damageand loss of life long before the buildingitself begins to burn, regardless of thetype of construction.

The Forest Products Laboratory hasconvincingly documented this fact forresidential construction. After studyingdwelling-room fires involving combus-tible contents, FPL concluded that“wall and ceiling materials, whethercombustible or noncombustible, hadlittle or no effect on the time or temper-ature of the critical point” – the point atwhich human life is untenable. In theFPL studies, the critical point wasreached in four to seven minutes. Othertests have shown untenable conditionscan occur in as little as two minutes.

Nor are so-called “fireproof” buildingmaterials a guarantee of human or prop-erty safety. One classic demonstration of this was the 1953 fire in GeneralMotors’ huge plant in Livonia, Michigan(photo right). The plant was consideredcompletely noncombustible, yet was acomplete loss due to the collapse ofunprotected metal construction.

Another was the 1967 disaster atMcCormick Place, Chicago’s exhibitionhall. All of its structural members,including interior nonbearing walls,were noncombustible. Yet a small firethat began in the contents spread withsuch heat that the entire ceiling fell assteel beams, girders and trusses buckledand collapsed.

The type of construction is, of course,important. But to protect the occupants– always the first concern – as well as tosafeguard property, the presence of aprompt detection and alarm system andthe accessibility of numerous exits are

far more vital. Also of importance arethe type of contents and furnishings,interior finishes, degree of sprinklerprotection and the availability of ade-quate fire-fighting equipment.

With proper construction in confor-mance with code regulations, and withrecognition of the above factors, a fire-safe building can be designed with bothcombustible and noncombustible mate-rials. This puts wood and wood struc-tural panel systems in perspective, andexplains why they are increasingly usedfor both low-rise and medium-rise (fourto six stories) construction today.

General Motors plant in Livonia, Michigan

was unprotected metalconstruction (see text).

5

THE BASICS OF

FIRE PROTECTION

Safety CriteriaIn order to evaluate fire safety of a struc-ture, building authorities consider manyfactors, including flame spread and fire-resistance ratings.

Flame Spread in general means spreadof fire within a room – and is measuredby the performance of the materialsused for interior finish on walls, ceilings,and partitions.

Flame spread is a property of thesurface material once fire has started,not the structure.

The best known flame spread test is thetunnel test, American Society for Testingand Materials (ASTM) Test MethodE-84. In this test, a sample of the mater-ial, 20 inches wide and 25 feet long, isinstalled as ceiling of a test chamber,and exposed to a gas flame at one end.The rate at which flame spreads acrossthe specimen is compared on a scale of0 for inorganic reinforced cement boardand 100 for red oak.

Another property measured in theASTM E-84 test is the opacity of thesmoke generated by the burning mater-ial. This measurement provides anindication of the amount of smokereleased, which also is compared on ascale of 0 for inorganic reinforcedcement board and 100 for red oak.

Model building code interior finishclassifications are summarized in Table 1. Materials with the lowest rate of flame spread (0 to 25) are classed byall building codes as Class A (or I), andare permitted for areas where fire hazardis most severe, such as vertical exitwaysof unsprinklered buildings for publicassembly.

Materials with ratings from 26 to 75 areClass B (or II) and are permitted in areasof intermediate severity: for example,corridors providing exitway access inbusiness and industrial buildings.

Materials rated from 76 to 200 are ClassC (or III). APA trademarked panels suchas plywood, oriented strand board(OSB) and composite panels fall gener-ally in this class and are permitted inrooms of most occupancies.(Exceptions: hospitals, or institutionswhere occupants are restrained.) Forexitways and for most interiors where

Class A or Class B flame spread perfor-mance is required, fire-retardant-treatedplywood (which falls in Class A) is permitted.

Table 1 also shows ratings of somecommonly used construction materials.Table 2 (page 6) shows typical flamespread requirements, as called for underthe International Building Code.

Table 1 shows that the flame spreadrating for construction plywood andAPA wood structural panels falls withinClass C; but there is considerable varia-tion of ratings, depending on species,thickness, and glue type. Plywood withexterior adhesives performs better thanwith interior; thick panels better thanthin; and low density species betterthan heavier species. (See Bibliographyin Appendix for references to more dataon flame spread tests, particularly APAResearch Report No. 128.)

TABLE 1

INTERIOR FINISH CLASSIFICATIONSInterior Finish Flame Spread Smoke

or Flame Spread Rating DevelopedClassification or Index Rating or Index

Class A (or I) 0 to 25Class B (or II) 26 to 75 450 max.Class C (or III) 76 to 200

Examples: Flame SmokeSpread Developed

Material Rating Rating

Inorganic reinforced cement board 0 0

Fire-retardant-treatedconstruction plywood 0 to 25 0 to 80

Fire-retardant-coated construction wood structural panels 0 to 45* 0 to 200

Fire-retardant-treated lumber 0 to 25 10 to 360

Red oak lumber 100 100

APA wood structural panels 76 to 200 25 to 270

*See text, page 9.

TABLE 2

TYPICAL FLAME SPREAD CLASSIFICATION REQUIREMENTS FOR INTERIOR FINISH BASED ON THE 2003 INTERNATIONALBUILDING CODE (TABLE 803.5)l

Sprinkleredm Nonsprinklered

Vertical exits Exit access Rooms and Vertical exits Exit access Rooms andand exit corridors and enclosed and exit corridors and enclosed

Group passagewaysa, b other exitways spacesc passagewaysa, b other exitways spacesc

A-1 & A-2 B B C A Ad Be

A-3f, A-4, A-5 B B C A Ad C

B, E, M, R-1, R-4 B C C A B C

F C C C B C C

H B B Cg A A B

I-1 B C C A B B

I-2 B B Bh, i A A B

I-3 A Ak C A A B

I-4 B B Bh, i A A B

R-2 C C C B B C

R-3 C C C C C C

S C C C B B C

U No restrictions No restrictions

For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2.

a. Class C interior finish materials shall be permitted for wainscotting or paneling of not more than 1,000 square feet of applied surface area in the grade lobbywhere applied directly to a noncombustible base or over furring strips applied to a noncombustible base and fireblocked as required by Section 803.4.1.

b. In vertical exits of buildings less than three stories in height of other than Group I-3, Class B interior finish for nonsprinklered buildings and Class C interiorfinish for sprinklered buildings shall be permitted.

c. Requirements for rooms and enclosed spaces shall be based upon spaces enclosed by partitions. Where a fire-resistance rating is required for structuralelements, the enclosing partitions shall extend from the floor to the ceiling. Partitions that do not comply with this shall be considered enclosing spaces and therooms or spaces on both sides shall be considered one. In determining the applicable requirements for rooms and enclosed spaces, the specific occupancythereof shall be the governing factor regardless of the group classification of the building or structure.

d. Lobby areas in A-1, A-2, and A-3 occupancies shall not be less than Class B materials.

e. Class C interior finish materials shall be permitted in places of assembly with an occupant load of 300 persons or less.

f. For churches and places of worship, wood used for ornamental purposes, trusses, paneling or chancel furnishing shall be permitted.

g. Class B material required where building exceeds two stories.

h. Class C interior finish materials shall be permitted in administrative spaces.

i. Class C interior finish materials shall be permitted in rooms with a capacity of four persons or less.

k. Class B materials shall be permitted as wainscotting extending not more than 48 inches above the finished floor in exit access corridors.

l. Finish materials as provided for in other sections of the code.

m. Applies when the vertical exits, exit passageways, exit access corridors or exitways, or rooms and spaces are protected by a sprinkler system installed inaccordance with Section 903.3.1.1 or 903.3.1.2.

6

1-1/8" APA RATED STURD-I-FLOOR

48 oc wood structural panel (tongue-and-groove edges)

Strength axis

Heavy timber or glulam beams(at least 4" nominal width)

Built-up roofing

7

Protection MethodsIn many cases, ordinary wood-frameconstruction with plywood or otherwood structural panel sheathing pro-vides ample fire safety and is completelyacceptable. When unusual circum-stances require additional protection,the designer’s options include protectedconstruction, Heavy Timber construc-tion, and treated construction.

Protected Construction is simply anynormal wood-and-panel assembly, suchas floor-ceiling or wall, with a fire-resis-tive material added to give primaryprotection to the joists. The materialmay be gypsum wallboard, plaster, oracoustical tile. The panel prevents flamepassage and temperature rise, whilereinforcing framing against collapseunder load. Table 3 (page 8) is an exam-ple of typical fire-resistive requirements.

Heavy Timber Construction implies theprotection provided by massive woodmembers. The name comes from earlyNew England textile mills, where it wasknown as “mill construction,” “plank-on-timber,” or “slow-burning.” In suchconstruction, though the outside maychar during exposure to fire, the surfacechar acts as insulation. And the strengthof wood is such that it continues tosupport its load – so the chance ofbuilding collapse is greatly diminished.

Based on comparative fire tests, 1-1/32-or 1-1/8-inch-thick wood structuralpanels with exterior glue are permittedfor heavy timber roof decks. SeeFigure 1 for typical construction; woodstructural panels must have tongue-and-groove edges. (See IBC Section 602.4.5and ICC Evaluation Service Inc., ReportNo. ER-1952.)

FIGURE 1

WOOD STRUCTURAL PANEL HEAVY TIMBER ROOF CONSTRUCTION

Fire Resistance. Though codes areconcerned with how fast fire can spreadon a room’s surface, they are even morespecific about fire resistance: the mea-sure of containment of fire within aroom or building. It is defined asprotection against fire penetrating awall, floor or roof, either directly orthrough a high rate of heat transfer thatmight cause combustible materials to beignited on the side of the wall or flooraway from the actual fire. Thus, it is aproperty of an assembly of several mate-rials, including fastenings, and of theworkmanship.

A fire-resistive construction gives timeto discover a fire, to suppress it beforeit spreads, and to evacuate the buildingif need be.

The standard test for measuring fireresistance is ASTM Test Method E-119.Ratings of assemblies are determined byactual fire-test procedures approximatingactual fire conditions. Floor-ceilings androof-ceilings are tested flat, while loadedto their full allowable stress. Walls aretested vertically, either as bearing walls,under axial load, or as nonbearing walls,under no load. The resistance rating isexpressed in hours or minutes that theconstruction withstands the test. So itapproximates the time the assemblywould be expected to withstand actualstructure-fire conditions.

A one-hour rating, for example, is takento mean that an assembly similar to thattested will not collapse, nor transmitflame or a high temperature, whilesupporting its full load, for at least one hour after the fire commences.

TABLE 4

DIMENSIONS OF COMPONENTS FOR HEAVY TIMBER CONSTRUCTION (TYPICAL CODE PROVISIONS)Heavy timber construction is generally defined in building codes and standards by the following minimum sizes for the various members orportions of a building:

8

Inches, nominal

ColumnsSupporting floor loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8x8Supporting roof and ceiling loads only. . . . . . . . . . . . . . . . . 6x8

Floor framingBeams and girders . . . . . . . . . . . . . . . . . . . . . 6 wide x 10 deepArches and trusses . . . . . . . . . . . . . . . . . . . . 8 in any dimension

Roof framing – not supporting floor loadsArches springing from grade . . . . . . . . . . . . . . . . 6x8 lower half

6x6 upper halfArches, trusses, other framing springing from top of walls, etc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4x6

Inches, nominal

Floor (covered with 1-inch nominal flooring, 15/32 or 1/2-inchwood structural panel, or other approved surfacing) Splined or tongue-and-groove plank. . . . . . . . . . . . . . . . . . . . 3Planks set on edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Roof decksSplined or tongue-and-groove plank. . . . . . . . . . . . . . . . . . . . 2Plank set on edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Tongue-and-groove wood structural panels . . . . . . . . . . 1-3/32

TABLE 3

TYPICAL FIRE-RESISTIVE REQUIREMENTS FOR STRUCTURAL COMPONENTS (IN HOURS, BASED ON 2003 INTERNATIONAL BUILDING CODE)

Type I Type II Type III Type IV Type V

Building Element A B A B A B HT A B

Structural frameIncluding columns, girders, trusses 3 2 1 0 1 0 HT 1 0

Bearing wallsExterior 3 2 1 0 2 2 2 1 0Interior 3 2 1 0 1 0 1/HT 1 0

Floor constructionIncluding supporting beams and joists 2 2 1 0 1 0 HT 1 0

Roof constructionIncluding supporting beams and joists 1-1/2 1 1 0 1 0 HT 1 0

Note: The above table specifies the fire resistance ratings required based on conditions such as maximum heights and areas. Increases and reductions in theseratings for specified design considerations are covered in the code. Nonbearing walls and partitions are typically not required to have a resistance rating.

A = Protected or one-hour.B = Unprotected.

9

This model code recognition can sim-plify roof construction practices whileproviding fire protection. Performanceof Heavy Timber construction ismarkedly superior to most unprotected“noncombustible” (metal) structures,under fire conditions. There are noconcealed spaces where fire can spread,making fire fighting simpler and safer.

The IBC and other model codes alsorecognize 15/32- or 1/2-inch woodstructural panels over 3-inch planks forHeavy Timber floors.

See Table 4 (page 8) for code definitionsof minimum sizes of members for HeavyTimber construction.

Treated Construction. In any projecteduse of fire-retardant treatments, thor-ough investigation should first deter-mine that it is the best overall solution,in view of long-term insurance costs andadequate fire protection at lowest con-struction cost. It is more expensive thanuntreated plywood and wood, which inmost cases perform satisfactorily inregard to both life safety and protectionof property.

FRT (fire-retardant-treated) wood orplywood is pressure-impregnated withchemicals in water solution to perm-anently inhibit combustion. This quali-fies it for lower flame spread (at least aslow as gypsum wallboard) and smoke-generation ratings, and reduces its fire-hazard classification. When it is identi-fied as such by a code-recognizedtesting agency label, it is rated on aparity with noncombustible construc-tions by many insurance rating bureaus,but not by building codes.

Precisely defined, FRT plywood hasbeen impregnated with fire-retardantchemicals in accordance with AmericanWood Preservers Association StandardAWPA C27. When tested for thirtyminutes under ASTM Standard E-84(the tunnel test), it has a flame spreadnot over 25 and shows no evidence ofsignificant progressive combustion.

Span Ratings and load capacities forAPA-trademarked plywood are basedon untreated panels, and may notapply following fire-retardant treat-ment. Obtain structural performancecharacteristics and use recommend-ations for FRT plywood from thecompany providing the treatmentand redrying service.

Fire Retardant (FR) Paints can be usedon plywood for nonstructural interiorfinish applications such as wall andceiling paneling, to reduce flame spreadratings to 25 or less (Class A or I), orfrom 26 to 75 (Class B or II) dependingon the paint selected. FR paints aretested per ASTM E-84 for ten minutes,as compared to thirty minutes for FRTplywood. FR paints can be applied asinterior finish coats over new or existingplywood surfaces; some FR paints areavailable with proprietary topcoat fin-ishes for exterior use.

Sprinklers are another option to solve a number of problems. With sprinklerprotection, code requirements for flamespread and fire-resistance ratings may be relaxed. It may be possible to addanother story or increase building area.Reduced insurance premiums for build-ings and contents mean that sprinklersgenerally will pay for themselves withina few years, depending on the value ofthe building and its contents. And thedifference in insurance rates betweensprinklered wood and sprinkleredunprotected steel buildings is usuallyvery small.

10

Meeting the Building CodesThe primary model building codes arethe International Building Code (IBC)and the International Residential Code(IRC). Other codes, currently beingsuperceded by the IBC and IRC, are theStandard Building Code (primarily usedin the South); Uniform Building Code(primarily used in the Midwest andWest); National Building Code (widelyused in the Northeast); and the Oneand Two Family Dwelling Code. TheIBC, IRC, and most of the regional andstate codes in the country are similar toor adaptations of these.

All code provisions have the authorityof law (unlike insurance requirements,which are optional).

All buildings must meet code specifica-tions as to maximum permissibleheights and floor areas. These specifi-cations are based on certain characteris-tics of the building, including the firezone; type of occupancy; constructionmaterials and systems; setbacks fromproperty lines; exits; and automaticextinguishing systems.

For further discussion of how to adjustthese characteristics in order to achievearea increases, see Appendix, “HowAreas Can Be Increased.”

Fire Zones. Some cities have establishedone, two or three geographic fire zones(or fire limits), which restrict type of useor occupancy, percentage of lot cover-age, and type of construction permitted.The purpose is to make fire protectioneasier by concentrating in one areathose buildings of similar fire hazard.Usually, frame construction is not

permitted in central fire zones, wherecongestion and closeness of other build-ings would make fire spread most likelyand fire fighting most difficult.

Occupancy. All codes have use or occu-pancy classifications; in general, theseinclude: residential, business, educa-tional, institutional, assembly, storage,mercantile, manufacturing, and haz-ardous. Within occupancy classifi-cations, codes also consider whether themanufacturing is of potentially explosiveor dangerous materials; whether theresidents are elderly, disabled, or con-fined; etc. Unprotected wood construc-tion is generally not permitted in suchoccupancies as high-hazard, theatreswith stages, and some institutions.

Setbacks. Codes recognize the advan-tage of large open areas around build-ings, to make fire fighting easier andprevent fire spread. Therefore, buildingsthat are 20 to 30 or more feet from theproperty line, or facing a street 20 ormore feet wide, are permitted largerareas than those immediately adjacentto other buildings.

Exits. The number and type of exitsrequired depend on occupant load andtravel distance to exits. For example,according to the International Residen-tial Code, in a business or residentialbuilding of unprotected frame construc-tion, maximum distance to an exit is200 feet. Other codes may differ some-what in these provisions. All exit assem-blies are classified by fire-resistanceratings, and except for certain high-hazard or institutional occupancies,wood construction is usually permitted.

Types of Construction. Construction-type classifications are based on fire-resistance ratings of structural elements.Of the three types of wood construc-tion, Heavy Timber, or Type IV, is usedin multistory buildings (up to five sto-ries) such as educational, religious,manufacturing, warehouse, supermar-ket; and permits largest areas. The nextlargest areas are permitted for Type III orordinary construction – commonly usedfor commercial or public buildings upto four or five stories high. Finally, light-frame construction or Type V is used in80 percent of all residential and manycommercial, institutional, industrialand assembly buildings.

Codes differ somewhat in the labelsthey apply to comparable types of construction. Actual codes should beconsulted for more detailed differences.

If the building requires a larger areathan is permitted for the type of con-struction selected, the designer hasseveral choices, including: breaking upthe area with fire walls, adding sprin-klers, increasing property line setbacks,or specifying a more fire-resistant con-struction. (See Appendix, “How AreasCan Be Increased.”)

Calculated Fire Resistance. The IBCand three of the model building codesalso permit determination of one-hourfire-rated wood-framed floors, roofs andload-bearing and non-bearing walls bycalculation, as an alternate to testedassemblies. These codes provide tablesof assigned times for components,which have been developed empiricallyfrom extensive studies of assembliestested in accordance with ASTM

11

Standard E-119. End-point criteria inthe standard also were considered. Aone-hour fire-rated assembly can bedetermined by combining the individualcomponent times of the assembly inaccordance with the method and limita-tions in the codes, thereby providingadditional choices for the designer.Methods also provide for determiningthe required size of glulam beams andcolumns for a one-hour fire resistancerating. Code references are:

■ 2003 International Building Code,Section 721.6

■ 1997 Uniform Building Code (UBC),Section 703.3 and UBC Standard 7-7,Parts V and VI

■ 1999 Standard Building Code,Section 709.6

■ Guidelines for Determining Fire-resistance Ratings of Building Elements(BOCA International, Inc./1994)

Insurance ProvisionsCompliance with insurance provisionsis purely voluntary. The means of doingso is not specified or even suggested bythe rating bureau. This puts a specialresponsibility on the designer to workout the best combination of economicalconstruction and sufficient protection toqualify for low premiums. And, if possi-ble, to determine during preliminaryplanning just what kind of rating can becounted on, while there is still time toadjust such factors as setbacks, materi-als, size, etc.

Most agencies will be glad to cooperatewith an architect who wishes to do thiskind of research (rating bureaus are

constrained to give out rate informationonly to, or by authority of, thebuilding owner).

Changing ideas about fire safety alsoobligate the designer to be familiar withthe many alternative means of assuringprotection. Awareness is increasing thatcontents, not structure, are most critical(due to many recent tragic fires in high-rise steel and concrete buildings). Moreemphasis is now being placed on warn-ing and sprinkler systems, less on “fire-proof” structural materials.

Furthermore, the greater likelihood ofcollapse of metal structures is beingrecognized, compared with sound woodconstruction. As a result, there is adefinite tendency to a lowering of ratesfor wood, and increasing them for metal.

This tendency is widespread, andhas been especially noticeable in theMidwest since 1969, where rates onunprotected metal have increased –possibly under the influence of suchincidents as the McCormick Place fire,and other adverse experiences.

Wind resistance of the building’s roofsystem also determines the ExtendedCoverage Endorsement, or ECE insur-ance rates. See the APA Design/Construction Guide: Nonresidential RoofSystems, Form A310, for wood roofsystems that provide maximum fire andwind protection, satisfy code require-ments, and qualify for lowest possibleinsurance rates. The publication isavailable on the APA web site.

Although insurance rates for wood buildingsare higher than for noncombustible build-ings, the savings in construction costs areusually enough to result in a substantiallyreduced annual cost.

Rating Bureaus and Rates. Insurancecompanies, through assessments againsttheir premium income, have for manyyears supported state and regional ratingbureaus throughout the country. Mostof these have been consolidated into theInsurance Services Office (ISO) and aredescribed at www.iso.com.

The intent of the ISO is to develop anationwide rate schedule, which willstraighten out much of the confusiondue to the multiplicity of rates through-out the country. However, until a gen-uinely universal rate schedule comesabout, it will still be necessary for arch-itects to be familiar with local situationsand to be alert to changes.

There are two kinds of rates: “class”rates (generally for one- and two-familyhomes, small multifamily, and garages),and “schedule” or specific rates (allother types of buildings). The former,with many shared physical characteris-tics, may be rated according to theirposition in established classes based ontype of construction, occupancy, andpublic fire protection. Only major differ-ences in these characteristics would bereason for rate distinction.

In the latter category, however, eachbuilding is considered a separate case. Itis rated after consideration of five factors:type of construction; effectiveness ofpublic fire protection; private fire protec-tion in the building; occupancy – thereare well over a hundred occupancyclasses, according to how the building isused, whether people are in it, etc.; andexposure from other properties nearby.

12

HOW TO BUILD FOR

FIRE PROTECTION

Wall SystemsPossible wood wall systems for light-frame construction include ordinarystud-wall, with sheathing or as singlewall (Sturd-I-Wall); “protected” con-struction; and incorporation of fire-retardant treatment or paint.

Unprotected double-wall or Sturd-I-Wallsystems, with studs on 16- or 24-inchcenters, are fully covered in the APAEngineered Wood Construction Guide (seeBibliography in Appendix).

Protected Walls. Protected light-frameconstruction with gypsum wallboardinterior finish is rated by codes betweenordinary (Type III) unprotected andHeavy Timber (Type IV) in terms of fireperformance. Examples of protectedconstruction are shown in Systems 2Aand 2C of Figure 2: 2x4 studs, 16inches or 24 inches o.c. with woodstructural panel siding over 5/8-inchType X gypsum sheathing on the exte-rior side and 5/8-inch Type X or propri-etary Type X (Type C or G) gypsumwallboard on the interior side. Anotheroption permitted in the Uniform

Building Code, using stucco over woodstructural panel sheathing, is shownin System 2B of Figure 2.

Protected wall constructions qualify forthe same ratings if other materials areadded: e.g., siding may be attached tothe outside of a rated wall to add shear-wall value, without impairing the rating.

The gypsum sheathing is not requiredunder the International Building Code,National Building Code and StandardBuilding Code where separation isgreater than 5 feet, since they providethat fire-resistive rating need only applyto the interior face of the wall. SeeSystems 2D through 2F of Figure 2 forone-hour fire-rated wall constructionsthat are applicable under these codeprovisions.

Model building code provisions alsopermit determination of one-hour fire-rated wall systems, using procedures forcalculated fire resistance of components(see page 10).

Interior Walls and Partitions. Generallyaccepted building code regulationsplace a flame spread limit of 200 (ClassC) on materials used for interior sur-faces (in areas other than certain exit-ways and corridors, as noted earlier).Since APA trademarked wood structural

panel ratings generally fall within ClassC, or 76-200, they are well within therange of acceptable materials.

For interior areas requiring lower flamespread ratings, fire-retardant-treated ply-wood paneling is acceptable; suchpanels qualifying for the U.L. label arecapable of a Class A rating, and areaccepted by codes. Fire retardant paints,properly applied, may also be used toreduce the flame spread rating to ClassA or B, and are often recognized bybuilding officials. (See page 10.)

In single-family residential use, Class Cis acceptable. Softwood plywood panel-ing is well within the acceptable range,and has been used for interior as well asexterior walls where plywood’s strengthand rigidity help the unit withstandhorizontal loads.

As for thermal resistance in fires:because of its superior insulating quali-ties, wood structural panels may beexpected to develop a finish resistance(based on time to develop an averagetemperature rise of 250° on the back ofthe panel) of approximately 20 or moreminutes per inch of thickness, whenexposed to the standard ASTM Time-Temperature curve. Pressure treatmentof plywood with fire retardant chemicalsdoes not materially affect the finish resis-tance, though coating with fire retardantpaints may be somewhat more effective.

13

FIGURE 2

ONE-HOUR COMBUSTIBLE LOAD-BEARING WALL ASSEMBLIES(a)

Some rated assemblies incorporate proprietary products. When designing and specifying, check the appropriate reference for complete details ona particular assembly. A change in details may affect the fire resistance of the assembly.

2A – LOAD-BEARING EXTERIOR WALL SYSTEM

Generic, nonproprietary assembly based on GA File No. WP8105 in Gypsum Association (G.A.) Fire Resistance Design Manual; applicablereferences in 1997 Uniform Building Code (Table No. 7-B), and 1999 Standard Building Code (Sec. 701.5.2). (2-Hour)b

APA Rated Siding Exterior5/8" Type X gypsum sheathingMineral wool or glass fiber insulation (optional)5/8" Type X gypsum wallboardMin. 2x4 studs @ 16" or 24" o.c.

2B – LOAD-BEARING EXTERIOR WALL SYSTEM

Generic, nonproprietary assembly based on combining Item No. 15-1.2 and 15-1.3 and Footnote l of Table 720.1(2) in the 2003 International Building Code. Also see Sec. 2.2.2 of ICC Evaluation Service, Inc. Report No. ER-1952.

Stucco (over self-furring metal lath)APA Rated Sheathing Exposure 1 plywood or OSB(c)(d)

Mineral wool or glass fiber insulation (optional)5/8" Type X gypsum wallboardMin. 2x4 studs @ 16" o.c.

2C – LOAD-BEARING EXTERIOR WALL SYSTEM

Based on U.L. Design No. U344 in Underwriters Laboratories Inc. (U.L.) Fire Resistance Directory.

APA Rated Siding Exterior or other exterior finish (code-approved type)5/8" Type X gypsum sheathingMin. 15/32" APA Rated Sheathing Exposure 1 OSB or plywood(d)

Glass fiber insulation (R11)5/8" proprietary(e) Type X gypsum wallboardMin. 2x4 studs @ 16" or 24" o.c.

2D – LOAD-BEARING EXTERIOR WALL SYSTEM

Based on U.L. Design No. U356 in Underwriters Laboratories Inc. (U.L.) Fire Resistance Directory.

APA Rated Siding Exterior or other exterior finish (code-approved type)Min. 7/16" APA Rated Sheathing Exposure 1 OSB or plywoodGlass fiber (R13) or mineral wool insulation5/8" Type X gypsum wallboardMin. 2x4 studs @ 16" o.c.

(a) Wall systems exposed to fire on both exterior and interior faces, exceptwhere indicated by “Fire Side” (tested from interior face only).

(b) For a two-hour load-bearing exterior wall of similar construction, see GAFile No. WP 8415 (requires two layers of 5/8" Type X gypsum sheathing onexterior side of wall, and two layers of 5/8" Type X gypsum wallboard oninterior side).

(c) See APA Engineered Wood Construction Guide (Form E30) for installation recommendations when stucco exterior finish is used. Building paper isrequired where stucco is applied over structural wood panel sheathing (check local building code and applicator for specific requirements). UniformBuilding Code requires two layers of waterproof building paper (per Federalspecification UU-B-790, Type 1, Grade D) over wood-based sheathing.

(d) Footnote l of Table No. 720.1(2) in the 2003 International Building Codepermits installation of wood structural panel sheathing directly over studs,beneath fire protective membrane, for added racking resistance or shear wallapplications, in certain generic, nonproprietary fire-rated wall assemblies.Also see ICC Evaluation Service, Inc. Report No. ER-1952 for wood structuralpanels used for wall sheathing in these assemblies.

(e) For proprietary names see latest U.L. Fire Resistance Directory, www.ul.com.

(figure continued on next page)

FIRE SIDE

14

FIGURE 2 CONTINUED

2E – LOAD-BEARING EXTERIOR WALL SYSTEM

Generic, nonproprietary assembly based on provisions for calculated fire resistance rating per Section 721.6 of the International ResidentialCode, Section 709.6.2.4 of the 1999 Standard Building Code, and Section 6.2 of Guidelines for Determining Fireresistance Ratings ofBuilding Elements (BOCA International, Inc./1994).

Min. 3/8" APA Rated Siding Exterior plywood(f )

Mineral wool or glass fiber insulation (optional)5/8" Type X gypsum wallboardMin. 2x4 studs @ 16" o.c.

2F – LOAD-BEARING EXTERIOR WALL SYSTEM

Based on U.L. Design Nos. U326, U330 (shown) and U335 (shown) in Underwriters Laboratories Inc. (U.L.) Fire Resistance Directory.

Min. 1/2" APA Rated Siding Exterior plywood1" Rigid foam insulation sheathingMineral wool insulation5/8" Type X gypsum wallboardMin. 2x4 studs @ 16" o.c.

Exterior finish-elastomeric coating1" Rigid foam insulation sheathingMin. 1/2" APA Rated Sheathing Exposure 1 plywood

Glass fiber insulation5/8" Type X gypsum wallboardMin. 2x4 studs @ 16" o.c.

2G – LOAD-BEARING INTERIOR (CHASE) WALL SYSTEM

Based on U.L. Design Nos. U339 and U341 (shown) in Underwriters Laboratories Inc. (U.L.) Fire Resistance Directory.

5/8" Type X gypsum wallboardMineral wool or glass fiber insulation (optional)

2x4 studs @ 16" or 24" o.c.5/8" Type X gypsum wallboard

Min. 1/2" APA Rated Sheathing Exposure 1 plywood

(f) Min. 5/16" APA Rated Sheathing Exposure 1 plywood, with building paperand APA Rated Siding Exterior or other exterior finish, or min. 3/8" APA RatedSiding Exterior directly over studs, may be used in accordance withTable 709.6.2C of the 1999 Standard Building Code.

FIRE SIDE (U330)

FIRE SIDE (U335)

1" Space

FIRE SIDE

FIGURE 3

TWO-HOUR LOAD-BEARING INTERIOR WALL SYSTEM

5/8" Type X gypsum wallboard2x6 studs @ 24" o.c.5-1/2" mineral wool

5/8" Type X gypsum wallboard

FIGURE 2 CONTINUED

2H – ONE-HOUR LOAD-BEARING INTERIOR WALL SYSTEM

5/8" Type X gypsum wallboard2x4 studs @ 16" o.c.3-1/2" mineral wool5/8" Type X gypsum wallboard

2I – ONE-HOUR LOAD-BEARING WALL SYSTEM

5/8" Type X gypsum wallboard2x6 studs @ 16" o.c.

5/8" Type X gypsum wallboard

2J – ONE-HOUR LOAD-BEARING INTERIOR WALL SYSTEM

5/8" Type X gypsum wallboard2x6 studs @ 16" o.c.5-1/2" mineral wool

5/8" Type X gypsum wallboard

2K – ONE-HOUR LOAD-BEARING EXTERIOR WALL SYSTEM

5/8" Type X gypsum wallboard2x6 studs @ 16" o.c.5-1/2" mineral wool

24/16 APA Exposure 1 sheathingAPA Siding – Panel or lap

15

FIRE SIDE

16

Floor and Roof SystemsRoof and floor systems that are acceptedby building codes, while providingmaximum strength and economy,include numerous constructions involv-ing APA-trademarked wood structuralpanels over a variety of support systems.Complete information on APA panelsheathing in general, and some twodozen roof and floor systems, may befound in APA’s Engineered WoodConstruction Guide, Form E30, (seeBibliography).

Two systems in particular that achievegood fire protection are protected, andHeavy Timber (see page 7). Examples ofprotected systems will be found on thefollowing pages.

Protected Roof-Ceiling and Floor-Ceiling Systems.There are numerous fire rated, speciallydesigned assemblies combining woodstructural panels with protective materi-als, suitable especially for commercialand public buildings. They include one-hour-rated and several two-hour-ratedprotected wood-frame wall and floor-ceiling systems.

Over 40 wood and plywood floor-ceiling (orroof-ceiling) systems are listed in the U.L.Fire Resistance Directory, and are acceptedas rated constructions by building codes.Examples are shown in Figure 4 (pages17-19). Model building code provisionsalso permit determination of one-hour

fire-rated floor-ceiling or roof-ceilingsystems, using procedures for calculat-ing fire resistance of components (seepage 10). Other proprietary floor-ceilingor roof-ceiling systems also are recog-nized by model building code agenciesunder evaluation reports issued to indi-vidual manufacturers or trade associa-tions.

Because they contain wood and maycontain other organic materials, they aredesignated as combustible construc-tions. At present, codes don’t permitthem in so-called “noncombustible”types of structures, even though theirtest performance is identical to that ofan assembly classed as noncombustible.

In these assemblies, materials such asgypsum wallboard, plaster, and acousti-cal tile provide primary fire protection.The panel floor or roof acts to preventflame passage and temperature rise, aswell as to reinforce joists against col-lapse under load after the effectivenessof the ceiling has been lost.

In many, a double layer of plywood(15/32 inch and 19/32 inch) is used,though several have a single layer of19/32 inch or thicker. Some modelcodes accept lightweight or gypsumconcrete under certain conditions inlieu of the top layer of plywood for one-hour floor-ceiling assemblies, as indi-cated in System 4.1 of Figure 4. Anyfinish floor material may be used. Mostcodes permit omission of the top layerof plywood in roof assemblies.

One assembly shown in System 4.2 ofFigure 4 (L513) permits an economical24-inch lumber joist spacing with asingle-layer 23/32" plywood floor, andseveral include trusses or I-joists(System 4.3).

Based on comparative tests, APA OSBmay be used in plywood floor-ceiling (orroof- ceiling) systems without jeopardiz-ing fire-resistance ratings. In double-layer wood systems, 7/16" OSB APARated Sheathing 24/16 may be used inlieu of 15/32" plywood subfloor. Othersubstitutions are based on equivalentpanel thickness.

Roof Coverings.The fire resistance ratings of finish roof-ing materials are listed as Class A, B, or Cin descending order of fire protectionafforded. Their use is prescribed bybuilding codes, and also affects insurancerates. The standard test for measuring thefire characteristics of roof coverings isASTM E108. Untreated APA RatedSheathing panels are recognized as a roofdeck substrate for rated roof coverings.For individual requirements, see the U.L.Roofing Materials and Systems Directory,Category TGFU for built-up or single ply roofing membranes or spray-appliedfoam insulation and roof coating systems; or Category TFWZ for pre-pared roof covering materials such asshingles, shakes, cement tile and metalroofing panels.

17

FIGURE 4

ONE-HOUR COMBUSTIBLE FLOOR-CEILING AND ROOF-CEILING ASSEMBLIES(f)(i)

Some rated assemblies incorporate proprietary products. When designing and specifying, check the Underwriters Laboratories Inc. (U.L.) Fire Resistance Directory for complete details on a particular assembly. A change in details may affect the fire resistance of the assembly.

4.1 TWO-LAYER FLOOR SYSTEM WITH JOISTS(a)(c)

For details, see U.L. Design Nos. L001, L003, L004, L005, L006, L201, L202, L206, L209, L210, L211 (2 hr), L212, L501, L502, L503, L505 (2 hr), L511 (2 hr), L512, L514, L515, L516, L519, L522, L523, L525, L526, L533, L535, L536 (2 hr), L537, L541 (2 hr) and L545. Alsosee U.L. Design Nos. L524 with steel joists spaced 24" o.c., L521 with wood trusses spaced 24" o.c. and L549 with steel trusses spaced 48" o.c.

4.2 – SINGLE-LAYER FLOOR SYSTEM WITH JOISTS

For details, see U.L. Design No. L513. Also see U.L. Design Nos. L504 for stressed-skin panel (5/8" APA RATED STURD-I-FLOOR orSHEATHING plywood with joists spaced 12" o.c.); L507 for 5/8" APA RATED STURD-I- FLOOR plywood with joists spaced 16" o.c.; L508 for1-1/8" APA RATED STURD-I-FLOOR plywood with joists spaced 48" o.c.; and L539, L540 with joists spaced 16" or 24" o.c. and separateceiling assembly (for modular housing units). Also see U.L. Design Nos. L524 and L543 with steel joists spaced 19.2" or 24" o.c. (L543 withseparate ceiling assembly).

* For proprietary names see latest U.L. Fire Resistance Directory.

See footnotes, page 20.

19/32" T&G APA plywood underlayment

Buildingpaper

15/32" APA woodstructural panel

subfloor(b)

Joists 16" o.c. (2x10s min.)

5/8"Type X gypsum wallboard ceiling

Lightweight or gypsum concretetopping (or gypsum wallboardU.L. Design Nos. L523 and L541, or cementitious tile backer unitsU.L. Design No. L545)

Buildingpaper

15/32" APA woodstructural panel

subfloor(b)

Joists 16" o.c. (2x10s min.)

5/8"Type X gypsum wallboard ceiling

4.1A 4.1B

Joists 24" o.c. (2x10s min.)(no bridging required)

23/32" T&G APA wood structural panels(b)

5/8" proprietary*Type X gypsum

wallboard ceiling

Constructionadhesive at joistsand T&G edges(e)

Resilient furringchannels max. 16" o.c.

18

4.3 – SINGLE-LAYER FLOOR SYSTEMS WITH I-JOISTS OR TRUSSES

For details, see U.L. Design Nos. L528, L529, L534, L542 and L548 with trusses or L544 with I-joists spaced 24" o.c. maximum. Also see GA File No. FC5512 for generic, nonproprietary truss assembly.

See footnotes, page 20.

FIGURE 4

ONE-HOUR COMBUSTIBLE FLOOR-CEILING AND ROOF-CEILING ASSEMBLIES(f)(i) (CONTINUED)

Min. 23/32" T&G APA Sturd-I-Floor Glued and nailed to I-joist

0.026" galvanized steel hat-shaped furring

channels max. 16" o.c.

Min. 1-1/2" mineral fiber batts (2.5 pcf)

Min. 9-1/4" wood I-joistsspaced max. 24" o.c.

with 3-1/2" x 1-1/2" flanges

Min. 5/8" Type Cgypsum wallboard

taped

For additional details, see AF&PA DCA 3 Assembly WIJ-1.1 (www.afandpa.org)

4.3A – ONE-HOUR FIRE-RESISTIVE FLOOR(g)/CEILING ASSEMBLY

Min. 23/32" T&G APA Sturd-I-Floor Glued and nailed to I-joist

0.019" galvanized steel resilient channels

max. 16" o.c.

Min. 1-1/2" mineral fiber batts (2.5 pcf)

Min. 5/8" Type Cgypsum wallboard

taped

Min. 9-1/4" wood I-joists spaced max. 24" o.c., 7/16" webs

with 3-1/2" x 1-1/2" flangesFor additional details, see AF&PA DCA 3, Assembly WIJ-1.2 (www.afandpa.org)

4.3B – ONE-HOUR FIRE-RESISTIVE FLOOR(g)/CEILING ASSEMBLY

Min. 23/32" T&G APA Sturd-I-Floor

0.019" galvanized steel resilient channels

max. 16" o.c.

Min. 2" mineral fiber batts (3.5 pcf)

1x4 wood setting strips

Min. 5/8" Type Cgypsum wallboard

taped

Min. 9-1/4" wood I-joistsspaced max. 24" o.c. with

min. 1-5/16" x 1-3/4" flanges

For additional details, see 2003 IBC Table 720.1(3), Item No. 24-1.1

4.3C – ONE-HOUR FIRE-RESISTIVE FLOOR(g)/CEILING ASSEMBLY

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

- - - -

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

- - 49(h) 59(h)

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

51(h) 46(h) 52 66

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

60(h) 48(h) 60(h) 60(h)

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

51(h) 46(h) 51(h) 64(h)

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

60(h) 50(h) 60(h) 65(h)

19

FIGURE 4

ONE-HOUR COMBUSTIBLE FLOOR-CEILING AND ROOF-CEILING ASSEMBLIES(f)(i) (CONTINUED)

Min. 23/32" T&G APA Sturd-I-Floor

0.019" galvanized steel hat-shaped furring channels

max. 24" o.c.

Min. 1" mineral fiber batts (6 pcf)

Min. 9-1/4" wood I-joistsspaced max. 24" o.c. with

2-1/4" x 1-1/2" flanges

Min. 1/2" Type Cgypsum wallboard

taped

For additional details, see AF&PA DCA 3, Assembly WIJ-1.4 (www.afandpa.org)

4.3D – ONE-HOUR FIRE-RESISTIVE FLOOR(g)/CEILING ASSEMBLY

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

- - 46 68

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

51 47 50 73

Min. 23/32" T&GAPA Sturd-I-Floor

Min. 9-1/4" wood I-joistsspaced max. 24" o.c. with

1-1/2" x 1-1/2" flanges

Two layers 1/2" Type Xgypsum wallboard

taped

For additional details, see AF&PA DCA 3, Assembly WIJ-1.5 (www.afandpa.org)

4.3E – ONE-HOUR FIRE-RESISTIVE FLOOR(g)/CEILING ASSEMBLY

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

- - - -

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

- - 49(h) 55(h)

0.019" galvanized steel resilient channels max. 16" o.c. (24" o.c. when joists max 16" o.c.)

Min. 23/32" T&G APA Sturd-I-Floor

Min. 9-1/2" wood I-joists spaced max. 24" o.c.

with 1-5/16" x 1-1/2" flanges

Insulation OK

Two layers1/2" Type X

gypsumwallboard

taped

Construction adhesiveat joists andT&G edges(e)

For additional details, see AF&PA DCA 3, Assembly WIJ-1.6 (www.afandpa.org)

4.3F – ONE-HOUR FIRE-RESISTIVE FLOOR(g)/CEILING ASSEMBLY

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

With Isulation 59 50 55(h) 68(h)

Without Isulation - - 54 68

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

With Isulation 65 51 63(h) 65(h)

Without Isulation - - 58(h) 55(h)

See footnotes, page 20.

20

(a) Substitution of 1-1/8" APA RATED STURD-I-FLOOR 48 oc for the combination ofsubfloor, paper and underlayment is often allowed. Check with local buildingofficial.

(b) Tests have shown that substitution of OSB or composite APA RATED SHEATHINGsubfloor and APA RATED STURD-I-FLOOR underlayment for the plywood panels inrated assemblies will not jeopardize fire-resistance ratings. Substitution is based onequivalent panel thickness, except that in two-layer wood assemblies 7/16" OSBsubfloor panels may be used in place of 15/32" plywood subfloor panels. OSBpanels are listed as alternates to plywood for subflooring or finish flooring in U.L.Design Nos. L501, L503, L505 (2hr), L508, L511 (2 hr), L513, L514, L516, L521,L526, L528, L529, L539, L540, L543 and L544.

(c) Most building codes do not require the top layer of two-layer rated assemblieswhen used for roofs.

(d) For improved acoustical performance, the gypsum wallboard is fastened toresilient metal channels in some assemblies. Other assemblies use mineral acousti-cal panels suspended under the floor framing on a T-bar grid system.

(e) Construction adhesive to conform to APA Specification AFG-01 (ASTM D3498).

(f) For other plywood floor-ceiling assemblies, see U.L. Design Nos. L208 (1-1/2hr),L506 (3/4 hr), L509 (1/2 hr), L520 (3/4 hr), L527 (1-1/2 hr) and L532 (1-1/2 hr).

(g) This assembly may also be used in a fire-rated roof/ceiling application, but onlywhen constructed exactly as described.

(h) STC and IIC values estimated by David L. Adams Associates, Inc.

(i) The following fire-rated floor-ceiling or roof-ceiling assemblies include thermal oracoustical insulation in the joist cavity:

InsulationU.L. Design No. Insulation Thickness (in.)L211 (2 hr) Glass fiber batts 6

L212 Glass fiber batts 6

L507 Mineral wool (blown in) 9-1/4

L516 Glass fiber batts 3

L520 (3/4 hr) Glass fiber batts 3

L521 Glass fiber batts 3-1/2

L532 (1-1/2 hr) Glass fiber batts 3-1/2

L533 Glass fiber batts 3

L539 Glass fiber batts 3-5/8

L540 Glass fiber batts 3-5/8

L541 (2 hr) Mineral wool batts 3

L543 Mineral wool (blown in) 3-1/2

L545 Glass fiber batts 3

FOOTNOTES FOR FIGURES 4 AND 5

FIGURE 5

TWO-HOUR COMBUSTIBLE FLOOR-CEILING AND ROOF-CEILING ASSEMBLIES(f)(i)

Min. 23/32" T&G APA Sturd-I-Floor

Min. 0.0179" galvanized steelhat-shaped furring channels

max. 16" o.c.

Min. 3-1/2" unfacedfiberglass insulation

on stay wires @ max. 12" o.c.

Stay wires max.12" o.c.

Three layers min. 5/8"

Type C gypsumwallboard taped

Min. 9-1/4" wood I-joistsspaced max. 24" o.c.,

min. 1-1/2" x 1-1/2" flanges

For additional details, see AF&PA DCA 3 Assembly WIJ-2.1 (www.afandpa.org)

STC AND IIC SOUND RATINGS

Without Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

- - 49(h) 54(h)

With Gypsum ConcreteCushioned Vinyl Carpet & Pad

STC IIC STC IIC

52(h) 46(h) 52(h) 60(h)

21

APA Rim Board Assemblies (One- and Two-Hour)See APA Data File No. D350, APA RimBoard in Fire Rated Assemblies, avail-able at www.apawood.org, for typicalassemblies, as shown below.

TABLE 5

MINIMUM DEPTH AT WHICH GLULAM BEAMS CAN BE ADAPTED FOR ONE-HOUR FIRE RATINGS

Depth DepthBeam Width 3 Sides Exposed 4 Sides Exposed

(in.) (in.) (in.)

5-1/8(a) 12 22-1/26-3/4 13-1/2 278-3/4 7-1/2 13-1/2

(a) When 5-1/8-inch wide glulam is used for one-hour fire-rated beams, load capacity is reduced toabout 50% of the allowable design load for depths shown in Table 5. Contact APA for details.

Assembly No. 1

1" APA Rim Board

Load

5/8" Type X GWB

One-Hour-Rated Wall

Upper story walls, floor/ceiling androof/ceiling, if present.

FIREFROM EITHER SIDE

Structural Glued Laminated Timber (Glulam)The requirements for Heavy Timberconstruction in model building codes donot constitute one-hour fire resistance.Procedures are available in the modelbuilding codes, however, to estimate thesize of glulam beams required for pro-jects in which one-hour fire resistance isrequired (see page 10).

A structural member’s fire resistance ismeasured by the time it can support itsdesign load during a fire. An exposedbeam or column sized for a minimumone-hour fire resistance will support itsfull design load for at least one hourduring standard fire test conditionswhich simulate an actual fire. As with all other structural framing, final specifi-cations of members designed to haveone-hour fire resistance should be care-fully checked by a professional engineeror architect to assure compliance withall local building codes.

For further information, see APA EWSTechnical Note EWS Y245, CalculatingFire Resistance of Glulam Beams andColumns.

Beams. Charring of glulam surfacesduring a fire places a premium on cross-sectional area. Charring weakens aglulam cross section slowly because ofthe self-insulating character of the char.Glulam beams with a minimum widthof 5-1/8 inches (nominal 6 inches) canbe adapted to a one-hour fire rating inaccordance with procedures recognizedby the model building codes.

For 6-3/4-inch and 8-3/4-inch widths,there is a minimum depth at and abovewhich all members with these widthscan be adapted at 100 percent of theallowable design load for a one-hour firerating. The minimum depth increaseswhen the design calls for the beam tobe exposed on four rather than threesides. See Table 5.

22

To adapt beams whose dimensionsqualify for one-hour fire rating, the basiclayup must be modified as shown inFigure 6. One core lamination must beremoved from the center and the ten-sion face augmented with the additionof a tension lamination.

Columns. Columns are often producedwith a single grade of laminationsthroughout and therefore need no spe-cial layup to qualify for a one-hour firerating. For glulam beams having8-3/4-inch and 10-3/4-inch widths,columns meeting the minimum sizestandard satisfy the one-hour fire ratingrequirement at 100 percent of the allowable design load.

However, column length plays a signifi-cant role in determining minimum sizefor one-hour ratings. The column sizeneeded for a one-hour fire rating isdetermined by calculating the l/d andthen using the appropriate minimumdimensions in Table 6.

l = column length in inches

d = column least dimension in inches

If l/d is less than or equal to 11, theminimum required size is smaller thanwhen l/d is greater than 11.

Metal Connectors for Glulam. Instructures using one-hour fire-ratedglulam, all supporting metal connectorsand fasteners must be protected toachieve a one-hour fire rating. A1-1/2 inch covering of wood, 5/8"Type X gypsum wallboard or any coatingapproved for a one-hour rating providesthe needed protection.

FIGURE 6

SIMPLE SPAN LAYUP

One tension lam added atbottom (replaces one corelam removed from center)

Compression lams at top

Core lams in center

Tension lams at bottom

One-Hour RatedBeam Layup

StandardBeam Layup

TABLE 6

MINIMUM DEPTH AT WHICH GLULAM COLUMNS QUALIFY FOR ONE-HOURRATING FOR GIVEN ll/D

Column Depth Depthll/d Width 3 Sides Exposed 4 Sides Exposed

Criteria (in.) (in.) (in.)

l/d>11 10-3/4 10-1/2 13-1/2

6-3/4(a) 10-1/2 10-1/2l/d≤ 11 8-3/4 7-1/2 12

10-3/4 7-1/2 10-1/2

(a) Glulam with a nominal width of 6-3/4 inches can be used for one-hour fire-rated columns, butload capacity is reduced to about 50% of the allowable design load for depths shown in Table 6.Contact APA for details.

23

APPENDIX

How Areas Can Be IncreasedBuilding codes place limitations on theheight and area of a building accordingto its compliance with certain estab-lished criteria which are based on codeconcern with health and safety ofthe occupants.

These criteria include occupancies,types of construction, and locationwithin fire zones.

Because light-frame construction is usually the best choice from thestandpoint of cost and simplicity, yetis accorded the lowest basic allowableareas, it is to the designer’s advantageto find ways to secure area increases,in order to take advantage of the econ-omy and versatility of wood andplywood construction.

The following suggestions, and the datain Table 7 (page 24), should help. Forfurther assistance on specific questions,designers should contact APA or its fieldspecialists in order to find ways toachieve area increases.

1. One-hour fire resistance: Codesallow the area of a wood-frame buildingto be increased when one-hour fireresistance is provided for all structuralelements in the building, includingbeams and columns, floors, walls, and roofs.

2. Automatic sprinkler protection: Allcodes have provisions which allowbuilding areas to be increased when anautomatic sprinkler system is installedthroughout the building. For example,under the International Building Code,a 300 percent increase is permitted for one-story buildings, and 200 per-cent for multi-story buildings. Anadditional benefit is the likelihood ofsubstantially lower insurance rateswith sprinklers. Sprinkler systems canbe connected to a central alarm systemfor additional protection.

3. Building separation: Basic areaincreases are allowed if there are largeopen areas on two or more sides of abuilding. Under the InternationalBuilding Code, a 175 percent increase isallowed if all sides face toward publicstreets.

4. Unlimited areas: In some codes,provisions are made for the constructionof unlimited area buildings for industrial,storage or business uses. Generally, theremust be large areas of open space sur-rounding the building, and the buildingmust be completely sprinklered.

The IBC permits unlimited areas incertain factory and storage buildings.The IBC also permits unlimited areas forall business, factory, mercantile andstorage occupancies when the buildingis one story and equipped with anautomatic sprinkler system.

5. Fire walls: The equivalent effect ofarea increases can be achieved by intro-duction of properly constructed firewalls. In effect, two contiguous build-ings are erected, but are separated by a rated wall or partition, withall openings protected.

24

TABLE 7

ALLOWABLE HEIGHT AND BUILDING AREASHeight limitations shown as stories and feet above grade plane. Area limitations as determined by the definition of “Area, building,” per floor.

Type of Construction

Type I Type II Type III Type IV Type V

A B A B A B HT A BHgt (feet)Group Hgt(S) UL 160 65 55 65 55 65 50 40

A-1S UL 5 3 2 3 2 3 2 1A UL UL 15,500 8,500 14,000 8,500 15,000 11,500 5,500

A-2S UL 11 3 2 3 2 3 2 1A UL UL 15,500 9,500 14,000 9,500 15,000 11,500 6,000

A-3S UL 11 3 2 3 2 3 2 1A UL UL 15,500 9,500 14,000 9,500 15,000 11,500 6,000

A-4S UL 11 3 2 3 2 3 2 1A UL UL 15,500 9,500 14,000 9,500 15,000 11,500 6,000

A-5S UL UL UL UL UL UL UL UL ULA UL UL UL UL UL UL UL UL UL

BS UL 11 5 4 5 4 5 3 2A UL UL 37,500 23,000 28,500 19,000 36,000 18,000 9,000

ES UL 5 3 2 3 2 3 1 1A UL UL 26,500 14,500 23,500 14,500 25,500 18,500 9,500

F-1S UL 11 4 2 3 2 4 2 1A UL UL 25,000 15,500 19,00 12,000 33,500 14,000 8,500

F-2S UL 11 5 3 4 3 5 3 2A UL UL 37,500 23,000 28,500 18,000 50,5000 21,000 13,000

H-1S 1 1 1 1 1 1 1 1 NPA 21,000 16,500 11,000 7,000 9,500 7,000 10,500 7,500 NP

H-2S UL 3 2 1 2 1 2 1 1A 21,000 16,500 11,000 7,000 9,500 7,000 10,500 7,500 3,000

H-3S UL 6 4 2 4 2 4 2 1A UL 60,000 26,500 14,000 17,500 13,000 25,500 10,000 5,000

H-4S UL 7 5 3 5 3 5 3 2A UL UL 37,500 17,500 28,500 17,500 36,000 18,000 6,500

H-5S 3 3 3 3 3 3 3 3 2A UL UL 37,500 23,000 28,500 19,000 36,000 18,000 9,000

I-1S UL 9 4 3 4 3 4 3 2A UL 55,000 19,000 10,000 16,500 10,000 18,000 10,500 4,500

I-2S UL 4 2 1 1 NP 1 1 NPA UL UL 15,000 11,000 12,000 NP 12,000 9,500 NP

I-3S UL 4 2 1 2 1 2 2 1A UL UL 15,000 11,000 10,500 7,500 12,000 7,500 5,000

I-4S UL 5 3 2 3 2 3 1 1A UL 60,500 26,500 13,000 23,500 13,000 25,500 18,500 9,000

MS UL 11 4 4 4 4 4 3 1A UL UL 21,500 12,500 18,500 12,500 20,500 14,000 9,000

CONTINUED ON NEXT PAGE

25

TABLE 7 CONTINUED

ALLOWABLE HEIGHT AND BUILDING AREASHeight limitations shown as stories and feet above grade plane. Area limitations as determined by the definition of “Area, building,” per floor.

Type of Construction

Type I Type II Type III Type IV Type V

A B A B A B HT A BHgt (feet)Group Hgt(S) UL 160 65 55 65 55 65 50 40

R-1S UL 11 4 4 4 4 4 3 2A UL UL 24,000 16,000 24,000 16,000 20,500 12,000 7,000

R-2a S UL 11 4 4 4 4 4 3 2A UL UL 24,000 16,000 24,000 16,000 20,500 12,000 7,000

R-3a S UL 11 4 4 4 4 4 3 3A UL UL UL UL UL UL UL UL UL

R-4S UL 11 4 4 4 4 4 3 2A UL UL 24,000 16,000 24,000 16,000 20,500 12,000 7,000

S-1S UL 11 4 3 3 3 4 3 1A UL 48,000 26,000 17,500 26,000 17,500 25,500 14,000 9,000

S-2b, c S UL 11 5 4 4 4 5 4 2A UL 79,000 39,000 26,000 39,000 26,000 38,500 21,000 13,500

US UL 5 4 2 3 2 4 2 1A UL 35,500 19,000 8,500 14,000 8,500 18,000 9,000 5,500

For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m2.

A = protected (fire resistive) or one-hour. B = no special requirements for fire resistance.

S = story, A = area.

UL = unlimited, NP = not permitted.

a. As applicable in Section 101.2.

b. Fore open parking structures, see Section 406.3.

c. For private garages, see Section 406.1.

26

BIBLIOGRAPHY

The following APA publicationscontain additional details onsubjects covered in this booklet.Copies are available upon requestfrom APA – The Engineered WoodAssociation, 7011 So. 19th St.,Tacoma, Washington 98466-5399.Or at www.apawood.org.APA Engineered Wood ConstructionGuide. E30, $8

APA Design/Construction Guide: Non-residential Roof Systems. A310. Onlineonly.

Research Report 128: Fire HazardClassification of PS-1 Plywood. Y380, $4

EWS Product Guide: Glulam.EWS X440, $3

In addition, the following are good sources of technical orbackground information on woodconstruction systems in relation to code provisions and insuranceregulations:Building Materials Directory (issuedannually). Underwriters LaboratoriesInc., Northbrook, Illinois. www.ul.com

Fire Resistance Directory (issued annu-ally). Underwriters Laboratories Inc.,Northbrook, Illinois. www.ul.com

Roofing Materials and Systems Directory(issued annually). UnderwritersLaboratories Inc., Northbrook, Illinois.www.ul.com

Fire Resistance of Engineered WoodRim Board Products, U.S. Forest ServiceResearch Paper FPL-RP-610, May 2003,Forest Products Laboratory, Madison,Wisconsin. www.fpl.fs.fed.us

DCA No. 3 – Fire Rated Wood WallAssemblies. American Forest and PaperAssociation, Washington, D.C.www.awc.org

DCA No. 4 – Component AdditiveMethod (CAM) for Calculating andDemonstrating Assembly FireEndurance. American Forest and PaperAssociation, Washington, D.C.www.awc.org

T. R. No. 10: Calculating the FireResistance of Exposed Wood Members.American Forest and Paper Association,Washington, D.C. www.awc.org

APA Engineered Wood Handbook,McGraw-Hill

Construction Costs and Fire Insurancefor Large Buildings. American Forestand Paper Association, Washington,D.C. www.awc.org

Other publications and information are available from:American Forest and Paper Association,Washington, D.C.

American Institute of Timber Construction, Englewood, Colorado.

American Society for Testing andMaterials, West Conshohocken,Pennsylvania.

U.S. Forest Products Laboratory,Madison, Wisconsin.

National Fire Protection Association,Quincy, Massachusetts.

Canadian Wood Council,Ottawa, Ontario, Canada.

Fire Resistance Design Manual, 2003.Gypsum Association, Washington, D.C.www.gypsum.org

Approval Guide (issued annually).Factory Mutual Research Corporation,Norwood, Massachusetts. www.allendale.com

Listings Book (issued annually). Intertek Testing Services/WarnockHersey Inc., Middleton, Wisconsin.www.et/semko.com

Fire Protection Handbook, 2003 Edition. National Fire ProtectionAssociation, Quincy, Massachusetts.www.nfpa.org

Effects of Wall Linings on Fire Per-formance within a Partially VentilatedCorridor. U.S. Forest Service ResearchPaper FPL 49, December, 1965. ForestProducts Laboratory, Madison,Wisconsin. www.fpl.fs.fed.us

Timber Construction Manual, 1994.American Institute of Timber Con-struction. Published by Wiley & Sons,New York.

Code Conforming Wood Design.American Forest and Paper Association,Washington, D.C. www.awc.org

WCD No. 5 – Heavy TimberConstruction Details. American Forestand Paper Association, Washington, D.C.www.awc.org

DCA No. 1 – Flame SpreadPerformance of Wood Products.American Forest and Paper Association,Washington, D.C. www.awc.org

DCA No. 2 – Design of Fire-ResistiveExposed Wood Members. AmericanForest and Paper Association,Washington, D.C. www.awc.org

27

ABOUT APA

APA – The Engineered Wood Associationis a nonprofit trade association whosemember mills produce the majority ofthe structural wood panel productsmanufactured in North America.

The Association’s trademarks appearonly on products manufactured bymember mills. The marks signify thatthe manufacturer is committed to APA’srigorous program of quality inspectionand testing and that panel quality issubject to verification throughAPA audit.

The audit procedures verify that themanufacturer is in conformance withAPA’s standards, set forth in APAPRP-108 “Performance Standards andPolicies for Structural-Use Panels,” orwith the Department of CommerceVoluntary Product Standards PS 1-95,

“Construction and Industrial Plywood”or PS 2-04, “Performance Standard forWood-Based Structural-Use Panels.”

APA’s services go far beyond qualitytesting and inspection. Research andpromotion programs play importantroles in developing and improving ply-wood and other panel constructionsystems, and in helping users and speci-fiers to better understand and applypanel products.

Always insist on panels bearing themark of quality – the APA trademark.Your APA panel purchase is not onlyyour highest possible assurance of prod-uct quality, but an investment in themany trade services that APA provideson your behalf.

The APA EWS trademark appears onlyon engineered wood products manu-factured by members of Engineered WoodSystems, a division of APA. The mark

signifies that the manufacturer is com-mitted to a rigorous program of qualityverification and testing and that prod-ucts are manufactured in conformancewith ANSI Standard A190.1, AmericanNational Standard for StructuralGlued Laminated Timber.

For additional information on woodconstruction systems, contact APA –The Engineered Wood Association, 7011 So. 19th St., Tacoma, Washington98466, or visit the Association’s website at www.apawoood.org

TYPICAL APA REGISTERED TRADEMARKS

TYPICAL APA EWS REGISTERED TRADEMARK

RATED SHEATHING

EXPOSURE 1SIZED FOR SPACING

32/16 15/32 INCH

000PRP-108 HUD-UM-40

THE ENGINEEREDWOOD ASSOCIATION

APA

RATED STURD-I-FLOOR

EXPOSURE 1

24 oc 23/32 INCH

000PRP-108 HUD-UM-40

THE ENGINEEREDWOOD ASSOCIATION

APA

SIZED FOR SPACINGT&G NET WIDTH 47-1/2

RATED SHEATHING

EXTERIORSIZED FOR SPACING

48/24 23/32 INCH

000PS 1-95 C-C PRP-108

THE ENGINEEREDWOOD ASSOCIATION

APA

RATED SHEATHING

EXPOSURE 1SIZED FOR SPACING

24/16 7/16 INCH

000PS 2-04 PRP-108

THE ENGINEEREDWOOD ASSOCIATION

APA

B IND DOUGLAS-FIR 117-9324F-V4

ANSI A190.1-1992MILL 0000

THE ENGINEEREDWOOD ASSOCIATION

APA

FIRE-RATED SYSTEMSDESIGN/CONSTRUCTION GUIDE

We have field representatives in many major U.S. cities and in Canada who can helpanswer questions involving APA trademarked

products. For additional assistance in specifyingAPA engineered wood products, contact us:

APA – THE ENGINEERED WOOD ASSOCIATION

HEADQUARTERS 7011 So. 19th St.

Tacoma, Washington 98466(253) 565-6600 ■ Fax: (253) 565-7265

PRODUCT SUPPORT HELP DESK(253) 620-7400

E-mail Address: help@apawood.org

DISCLAIMERThe information contained herein is based on APA –The Engineered Wood Association’s continuing pro-grams of laboratory testing, product research, andcomprehensive field experience. Neither APA, norits members make any warranty, expressed orimplied, or assume any legal liability or responsibil-ity for the use, application of, and/or reference toopinions, findings, conclusions, or recommenda-tions included in this publication. Consult your localjurisdiction or design professional to assure compli-ance with code, construction, and performancerequirements. Because APA has no control overquality of workmanship or the conditions underwhich engineered wood products are used, it can-not accept responsibility for product performance ordesigns as actually constructed.

Form No. W305YRevised June 2005/0300

www.apawood.org@Web Address: