oriented strand board

P R O D U C T G U I D E

A P AThe Eng ine e r ed Wood As so c i a t i on

O R I E N T E DS T R A N D B O A R D

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Wood is good. It is the earth’s natural, energy efficient and renewable building material.

Engineered wood is a better use of wood. It uses less wood to make more wood products.

That’s why using APA trademarked plywood, oriented strand board and APA EWSglued laminated timbers is the right thing to do.

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 731 million acres issuitable for repeated planting and harvesting of timber. But only about half of the landsuitable for growing timber is open to logging. Most of that harvestable acreage is opento other uses, such as camping, hiking, hunting, etc. Forests fully cover one-half ofCanada’s land mass. Of this forestland, nearly half is considered productive, or capableof producing timber on a sustained yield basis. Canada has the highest per capitaaccumulation of protected natural areas in the world – areas including national andprovincial parks.

■ We’re growing more wood every day. American landowners plant more thantwo billion trees every year. In addition, millions of trees seed naturally. The forestproducts industry, which comprises about 15 percent of forestland ownership, isresponsible for 41 percent of replanted forest acreage. That works out to more than one billion trees a year, or about three million trees planted every day. This high rate ofreplanting accounts for the fact that each year, 27 percent more timber is grown than isharvested. The Canadian forest products industry annually harvests only 4/10 of onepercent of the country’s productive forestlands. Canada’s replanting record shows afourfold increase in the number of trees planted between 1975 and 1990.

■ Manufacturing wood is energyefficient. Wood products made up47 percent of all industrial raw materialsmanufactured in the United States, yetconsumed only 4 percent of the energyneeded to manufacture all industrial rawmaterials, according to a 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 of carbon dioxide.

Wood. It’s the right product for the environment.

D O T H E R I G H T T H I N G R I G H T ™


Percent of Percent ofMaterial Production Energy Use

Wood 47 4

Steel 23 48

Aluminum 2 8

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

RATED STURD-I-FLOOR

EXPOSURE 124 oc 23/32 INCH

000PS 2-92 SINGLE FLOOR

PRP-108 HUD-UM-40

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PG,W410,OSB.0 4/17/00 7:12 AM

CONTENTS

Product Features . . . . . . . . . . . . 4

Quality Assurance . . . . . . . . . . . 6

OSB Applicationsand Common Sizes . . . . . . . . . . 7

Span Ratings . . . . . . . . . . . . . . .9

OSB Storage and Handling . . .11

APA Provides Quality Assurance and More . . . . . . . .11

rom squeak-free floors to solid wall and

roof sheathing, oriented strand board (OSB)

is helping to shape how the world builds.

OSB is engineered for strength and designed

for a variety of applications. For about two decades,

OSB has been a proven performer for many

residential and nonresidential applications. Its

performance has allowed OSB to gain entry into

new markets, including materials-handling

applications, the structural insulated panel

industry, do-it-yourself projects, wood I-joist

products, and industrial applications such as

furniture, and trailer liners.

This brochure from APA – The Engineered

Wood Association describes OSB’s features,

uses, quality assurance, and performance. APA

began providing a quality assurance program for

OSB in 1981 and has led the engineered wood

industry in OSB research and quality programs

ever since. The APA trademark is the manufac-

turer’s assurance to you that the OSB panel is

produced to APA’s stringent requirements as well

as to U.S. and Canadian standard requirements.

The APA trademark also assures you that an OSB

manufacturer is committed to quality.

F

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PRODUCT FEATURES

OSB is made from real wood

OSB is manufactured in a cross-orientedpattern similar to plywood to create astrong, stiff structural panel. OSB iscomposed of thin rectangular-shapedwood strands arranged in layers at rightangles to one another, which are laid upinto mats that form a panel. OSB isbonded with fully waterproof adhesives.Most panels are also treated with asealant on the panel edges to guardagainst moisture penetration duringshipment. As an added feature, panelsare often textured on at least one side toprovide a slip-resistant surface.

the correct size. The dried strands aresprayed with liquid or powder resin andthen transported in layers on a conveyersystem to a forming line, where thelayers are cross-oriented into mats. Forface layers, the strands generally runalong the panel, while for core layers, thestrands are randomly oriented or runacross the panel. The mats are trimmedto a workable size and then moved to apress where the wood strands and glueare bonded together under heat andpressure to create a structural panel.Finally, the panels are cut to size. Panelscan be manufactured in many sizessimply by altering the cutting pattern.

OSB uses the wood resource very effi-ciently, in part because sheathing panelscan be made using smaller, younger fast-growing tree species such as aspen andsouthern yellow pine. Plus, about 85-90 percent of a log can be used to makehigh quality structural panels, and theremainder – bark, saw trim, and saw-dust – can be converted into energy,pulp chips or bark dust.

OSB manufactureIn the first phase of OSB manufacture,logs are debarked and cut to a uniformlength. The logs are then turned intostrands or wafers. The strands are driedwith heat in a large rotating drum whichis screened to grade for strands that are

4

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5

OSB is engineered to performOver a decade of laboratory tests anduse in the field have proven that OSB isan excellent performer. Performancebegins when the panel leaves the manu-facturer. The panels remain flat andsquare during storage and transporta-tion, so they arrive at the jobsite flat andeasy to install; tongue-and-groove panelseffortlessly fit together. Relative to theirstrength, OSB panels are light in weightand easy to handle and install.Frequently, the panels are textured orsplatter-coated on one side to increasetraction on the panel surface. This isespecially useful when the panels areused for roof sheathing, because the

textured surface provides better footingfor workers. OSB is designed to with-stand exposure to the weather duringconstruction.

OSB’s performance continues long after the panel is put to use. The panelsexhibit excellent fastener-holding capa-bility, even when nailed close to thepanel edge. OSB resists deflection,delamination and warping because thewood and adhesives work together tocreate a strong, dimensionally stablepanel. OSB panels are made of real

wood, a natural insulator which provides excellent protection againstheat loss and condensation. Many OSBpanels are manufactured in large dimen-sions, minimizing the number of jointsthat can “leak” heat and admit airbornenoise into the structure. In addition, the panels resist racking and shapedistortion under high wind andearthquake forces.

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FIGURE 1

TYPICAL APA TRADEMARK

1 APA panel grade2 Span rating3 Exposure durability classification4 Thickness5 Mill number6 APA’s performance-rated panel standard

QUALITY ASSURANCE

OSB panels that bear the APA trademarkare manufactured under APA’s rigorousquality assurance program, and arerecognized by the major U.S. andCanadian building codes, as well asmany international building codes. Each panel is “performance rated,”which means the panel meets the performance requirements necessary for its end-use application.

Standards recognition in the United StatesMost North American OSB panels are manufactured in conformance withVoluntary Product Standard PS-2 or APAPRP-108 performance standards. Panels,similar to those described in the repre-sentative trademarks in Figure 1, areevaluated for their performance in spe-cific end-use markets. Panel applicationsdescribed in PS-2 and APA PRP-108include floors, walls, and roofs. Thesestandards are recognized in the majormodel building codes in the UnitedStates: 1) National Building Code,2) Uniform Building Code, 3) StandardBuilding Code, and the InternationalBuilding Code* and InternationalResidential Code*, or by NationalEvaluation Service Report NER-108.

* Scheduled for publication in the year 2000.

FIGURE 2

TYPICAL APA TRADEMARK, CONFORMING TO CSA-O325

1 APA panel grade2 Panel mark – Rating and end-use designation, Canadian standard3 Canadian performance-rated panel standard4 Thickness5 Mill number

RATED SHEATHING

EXPOSURE 1SIZED FOR SPACING

32/16 15/32 INCH

000PRP-108 HUD-UM-40

THE ENGINEEREDWOOD ASSOCIATION

APA

RATED SHEATHING

EXPOSURE 1

10.5mmCSA 0325

EXTERIOR TYPEADHESIVE

SIZED FOR SPACING

24/16 7/16 INCH

CONSTRUCTION SHEATHING

1R24/2F16/W24

000PS 2-92 SHEATHINGPRP-108 HUD-UM-40

THE ENGINEEREDWOOD ASSOCIATION

APA

STRENGTH AXISTHIS DIRECTION

12

3

4

56

1

2

3

5

4

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7

Standards recognition in CanadaMany North American OSB panels aremanufactured in conformance to therequirements of CAN/CSA-O325.0-92Construction Sheathing. The paneltrademark shown in Figure 2 is repre-sentative of the marks APA applies to OSB manufactured in accor-dance with the Canadian standard. OSB panels manufactured to theCAN/CSA-O325.0-92 standard arerecognized in the National BuildingCode of Canada and other provincialcodes for use in flooring, wall, androof construction.

Performance standardsA performance standard sets perfor-mance requirements for a product basedon that product’s intended end use.The advantage of a wood structuralpanel performance standard is that itprovides a common baseline of perfor-mance for all panel types, regardless ofthe manufacturing method. By placingemphasis on product performancerather than on manufacturing method,you – the consumer – stand to benefit.

A performance standard sets require-ments based on a panel’s end use, whilea prescriptive standard defines mini-mum manufacturing requirements. Theobjective of a performance standard is to provide flexibility in manufacturingwhile assuring that a product will satisfythe requirements of the intended use.

Performance standards help to encour-age more efficient use of resourcesbecause panel producers have morefreedom to use innovative manufactur-ing techniques that use greater percent-ages of each log and allow for theutilization of a wide range of species.

The wood products industry was notthe first to use performance standardsand testing. The electronics, automo-

1.25 x 2.50 meters. Panels for use asexterior siding are also available innarrow lap widths of 6 inches (152 mm)or 8 inches (203 mm) and 16-foot(4.88 m) lengths. Because OSB istypically manufactured in large sizes,many manufacturers can custom-makepanels in almost any size by simplyaltering the cutting pattern. Most OSBmanufacturers make oversized panels,up to 8 x 24 feet, which are typicallyused for panelized roof systems or mod-ular floors. In operations where over-sized panels can be handled, theyprovide the advantage of reducing thetotal number of panels required to do ajob, and thus speed installationtime and cost.

OSB can be manufactured with squareedges or with tongue-and-groove edges.Panel surface treatments may includetexturing or sanding. Overlaid OSB foruse as exterior siding also may be surface textured or grooved.

Exposure classificationsAPA Performance Rated oriented strandboard panels have a designated expo-sure classification, which identifies thepanel’s resistance to moisture exposure.

Panels are classified into the followingtwo groups:

Exterior panels have a fully waterproofbond and are designed for applicationssubject to permanent exposure to theweather or to moisture.

Exposure 1 panels have a fully water-proof bond and are designed for appli-cations where long construction delaysmay be expected prior to providingprotection. Approximately 95 percent ofPerformance Rated Panels are manufac-tured with this designation.

tive, and aircraft industries all use per-formance standards for a variety of partsand products. Panels manufacturedunder APA performance standards arerated for three end uses: sheathing forfloors, walls, and roofs (APA RatedSheathing); single-layer flooring (APARated Sturd-I-Floor); and exterior siding(APA Rated Siding).

The three basic criteria for qualifyingOSB products under APA performancestandards are: structural adequacy,dimensional stability, and bond durabil-ity. Performance criteria in each of thesecategories were established by buildingcode requirements and through tests ofpanel products with known acceptancein the marketplace. These tests assurethat panels possess the structuralrequirements necessary for uniformload, concentrated load, shear wall,diaphragm, and other demanding end-use applications. A partial list of typicaltests includes: linear expansion, racking,uniform load, concentrated static load,impact resistance, direct fastener with-drawal, and lateral fastener strength.

OSB APPLICATIONS

AND COMMON SIZES

OSB is most commonly used for tradi-tional applications such as sheathing forroofs and walls, subfloors, and single-layer flooring. Its superior performancehas allowed OSB to gain popularity in avariety of other areas, including: struc-tural insulated panels, the webs forwood I-joists, materials-handling appli-cations, furniture, and a variety of do-it-yourself projects.

OSB panels manufactured in NorthAmerica are typically 4 x 8 feetin size. Metric panel sizes are alsoavailable from some manufacturers in

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8

OSB for sheathingOSB APA Rated Sheathing is intendedfor subflooring, wall sheathing, and roofsheathing. APA Rated Sheathing/CeilingDeck can also be made using OSB; it ismade so that one surface has an overlay,texturing, or grooving.

Common thicknesses for sheathingpanels are: 5/16" (7.9 mm), 3/8" (9.5 mm), 7/16" (11.1 mm),15/32" (11.9 mm), 1/2" (12.7 mm),19/32" (15.1 mm), 5/8" (15.9 mm),23/32" (18.2 mm), and 3/4" (19.0 mm).

OSB for flooringOSB APA Rated Sturd-I-Floor isintended for single-layer flooring under carpet and pad. APA Rated Sturd-I-Floor panels often have tongue-and-groove edges.

Common thicknesses for flooring panelsare: 19/32" (15.1 mm), 5/8" (15.9 mm),23/32" (18.2 mm), 3/4" (19.0 mm),7/8" (22.2 mm), 1" (25.4 mm), and1-1/8" (28.6 mm).

OSB for industrial and do-it-yourself applicationsOSB is also widely used in industrialapplications. It can be used for mezza-nine floors and shelving in commercialand industrial structures. OSB also isused in furniture, reels, trailer liners,recreational vehicle floors, roofs andcomponents. Industrial specifiers areencouraged to talk with APA mills abouttheir particular panel needs.

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SPAN RATINGS

Span Ratings for panels used in the United StatesThe Span Ratings in the trademarks onPerformance Rated Panels denote themaximum permitted center-to-centerspacing of supports, in inches, overwhich the panels should be installed innormal construction.

For APA Rated Sheathing and Sturd-I-Floor, the Span Rating applies when thelong panel dimension is across sup-ports, unless the strength axis is other-wise identified. The Span Rating for APA Rated Siding panels is for verticalinstallation; for lap siding, the ratingapplies with the long dimensionacross supports.

For APA Rated Sheathing, the SpanRating looks like a fraction, such as32/16. The left-hand number denotesthe maximum spacing of supports (ininches) when the panel is used for roofsheathing, and the right-hand numberdenotes the maximum spacing of supports when the panel is used for subflooring.

Sheathing panels with roof Span Ratingsof 24 or greater may be used verticallyor horizontally as wall sheathing overstuds at 24 inches on center (o.c.).Those with roof Span Ratings of lessthan 24 may be used vertically or hori-zontally over studs at 16 inches o.c.

APA Rated Sheathing may also be manufactured specifically for use as wall sheathing. These panels are identified with Span Ratings of Wall-16 or Wall-24.

over which the panels should beinstalled. The Span Rating, also referredto as “panel mark,” applies when thelong panel dimension runs across thesupports, unless the strength axis isotherwise identified.

APA Rated Sheathing and APA RatedSturd-I-Floor panels intended for use inCanada are marked with one or moreSpan Ratings to show maximum supportspacings for subfloors, roofs, and/orwalls. Span Ratings for floors and roofsinclude a number and letter to indicatethe end use, followed by a two-digitnumber, or span mark, representing themaximum allowable span in inches. An“F” in the Span Rating represents floors,while the “R” signifies roofs. In the caseof floors, the prefix “1” indicates that thepanel is designed for use as a single-layerfloor (no separate underlay requiredunder carpet and pad); a “2” indicatesthat an additional layer of panel-typeunderlay is required. For example, 2F16is a Span Rating for a two-layer subfloor-ing system (subfloor with underlay to beadded), where supports are spaced amaximum of 16 inches on centre.

For roofs, the prefix “1” indicates thatno additional edge support is requiredat maximum span; a panel with a “2”will require edge support such as panelclips at maximum span. A Span Ratingof 2R24, therefore, represents use forroof applications with panel clips wheresupports are spaced a maximum of24 inches on centre.

APA Rated Sheathing Span Ratings forwalls include the letter “W” to identifyend use followed by a two-digit number,

APA Rated Sturd-I-Floor panels aredesigned specifically for single-floor(combined subfloor-underlayment)applications under carpet and pad andare manufactured with Span Ratings of16, 20, 24, 32, and 48 oc.

APA Rated Siding is produced withSpan Ratings of 16 and 24 oc. Bothpanels and lap siding may be useddirect to studs or over non-structuralsheathing (Sturd-I-Wall construction) orover nailable panel or lumber sheathing(double wall construction).

Building precisely at Span Ratings willmeet minimum code requirements. Forstructures that will exceed minimumcode requirements, specify panels withSpan Ratings greater than the spacingof supports.

Allowable uniformly distributed liveload at maximum span for APA RatedSturd-I-Floor and APA Rated Sheathingis 100 psf live load for floors plus 10 psfdead load (65 psf total load for Sturd-I-Floor 48 oc) and 30 psf snow load forroofs (35 psf for Rated Sheathing 48/24or greater) plus 10 psf dead load. Higherlive load levels can be achieved by plac-ing supports closer than the maximumspan indicated on the APA RatedSheathing or Sturd-I-Floor trademarks.Refer to APA’s Design/Construction Guide:Residential and Commercial for these liveload capacities.

Span Ratings for panels used in CanadaThe Span Ratings in the trademarks onPerformance Rated Panels denote themaximum recommended centre-to-centre spacing of supports, in inches,

9

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indicating the maximum supportspacing. For example, a Span Rating ofW16 appears on panels for use wherethe maximum spacing of wall framingmembers is 16 inches on centre.

Building at the indicated Span Ratingswill ensure that minimum code require-ments are met. For structures that willexceed minimum code requirements,specify panels with Span Ratings greaterthan the spacing of supports.

Allowable uniformly distributed liveload at maximum span for APA RatedSturd-I-Floor and APA Rated Sheathingis 4.8 kPa (100 psf) for floors plus0.5 kPa (10 psf) dead load (3.1 kPa[65 psf] total load for Sturd-I-Floor1F48) and 1.4 kPa (30 psf) for roofs(1.7 kPa [35 psf] for Rated Sheathing2R48) plus 0.5 kPa (10 psf) dead load.Higher live load levels can be achievedby placing supports closer than themaximum span indicated on the APARated Sheathing or Sturd-I-Floor trade-marks. Refer to APA’s Design/Construction Guide: Residential andCommercial, Form E30, or to theResidential Construction Guide, CanadianEdition, form CE R200 (English) orForm CF R200 (French) for theselive load levels.

PANEL MARKS FOR CONSTRUCTION SHEATHING PRODUCTS

Manufactured under Canadian Standard CAN/CSA-O325.0-92

TABLE 1

END-USE MARKSFor Panels Marked Assumed End Use

1F Subflooring (single-layer)

2F Subflooring used with panel-type underlay

1R Roof sheathing used without edge support

2R Roof sheathing used with edge support

W Wall sheathing

TABLE 2

PANEL MARKSSpan Marks

16 20 24 32 40 48Recommended Framing Member Spacing

End Use 400 mm 500 mm 600 mm 800 mm 1000 mm 1200 mmMarks (16 in.) (20 in.) (24 in.) (32 in.) (40 in.) (48 in.)

1F 1F16 1F20 1F24 1F32 * 1F48

2F 2F16 2F20 2F24 * * *

1R 1R16 1R20 1R24 1R32 1R40 1R48

2R 2R16 2R20 2R24 2R32 2R40 2R48

W W16 W20 W24 * * *

* Not covered in CSA-O325

Note: (1) Multiple panel marks may be used on panels qualified for more than one end use,e.g., 1R24/2F16/W24 or 2R48/2F24.

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OSB STORAGE

AND HANDLING

OSB panels require proper storage and handling. Always protect ends and edges, especially tongue-and-grooveproducts, from physical damage. Whenmoving bundles of panels with a forklift,place the bundles on pallets or lumberbunks to avoid damaging them withfork tines. When transporting panels on open truck beds, cover the bundles with a tarp.

Whenever possible, store the panelsunder a cover. Keep sanded or otherappearance-grade panels away from hightraffic areas. If moisture absorption isexpected, cut the steel band on thebundles to prevent damage.

When storing panels outside, stackthem on a level surface on top ofstringers or other blocking. Use at leastthree stringers. Never leave panels incontact with the ground. Cover thestack with plastic or a tarp. Make surethe bundle is well ventilated toprevent mildew.

APA PROVIDES

QUALITY ASSURANCE

AND MORE

APA – The Engineered Wood Associationis a nonprofit trade association whosemember mills produce approximately70 percent of the structural wood panel products manufactured inNorth America.

■ Conducts informational buyer andspecifier seminars and provides dealerand distributor sales training.

■ Publishes a vast inventory of literatureon panel grades, applications, designcriteria, and scores of other topics.

■ Advertises and publicizes panelproduct systems and applications innational trade and consumer magazines.

■ Works to secure acceptance ofstructural wood panel products andapplications by code officials, insuringagencies and lending institutions.

■ Develops and maintains industryperformance and product standards.

■ Conducts in-depth market researchand development programs to identifyand penetrate new panel markets.

■ Works in conjunction with otherwood product industry organizations on solutions to problems ofcommon concern.

Always insist on panels bearing themark of quality – the APA trademark.Your APA panel purchase or specifica-tion is your highest assurance of quality.It is also an investment in the manytrade services and programs that APAundertakes on your behalf.

Founded in 1933 as the Douglas FirPlywood Association and widely recog-nized today as the voice of the structuralwood panel industry, APA performsnumerous functions and services onbehalf of panel product users, specifiers,dealers, distributors, schools, universities,and other key groups.

Among the most important of thesefunctions is quality auditing. The APAtrademark appears only on productsmanufactured by APA member mills and is the manufacturer’s assurance thatthe product conforms to the standardshown on the trademark. For OSB, thatstandard may be an APA performancestandard, Voluntary Product StandardPS 2-92 Performance Standard forWood-Based Structural-Use Panels, orCAN/CSA-O325.0-92 ConstructionSheathing. APA maintains five qualitytesting laboratories in key producingregions, and a 37,000-square-footresearch center at Association headquar-ters in Tacoma, Washington.

But quality validation is only one of APA’s many functions. TheAssociation also:

■ Operates the most sophisticatedprogram for basic panel researchin the world.

■ Maintains an international network offield representatives to assist panelproduct users, specifiers, dealers,distributors, and other segmentsof the trade.

11

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OR I EN T ED S TRAND BOARDP R O D U C T G U I D E

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

products. For additional assistance in specifyingAPA engineered wood products, get in touch with

your nearest APA regional office. Call or write:

WESTERN REGION7011 So. 19th St. ■ P.O. Box 11700Tacoma, Washington 98411-0700

(253) 565-6600 ■ Fax: (253) 565-7265

EASTERN REGION2130 Barrett Park Drive, Suite 102Kennesaw, Georgia 30144-3681

(770) 427-9371 ■ Fax: (770) 423-1703

U.S. HEADQUARTERS AND INTERNATIONAL MARKETING DIVISION

7011 So. 19th St. ■ P.O. Box 11700Tacoma, Washington 98411-0700

(253) 565-6600 ■ Fax: (253) 565-7265

PRODUCT SUPPORT HELP DESK(253) 620-7400

E-mail Address: [email protected]

(Offices: Antwerp, Belgium; Bournemouth,United Kingdom; Hamburg, Germany; Mexico City,

Mexico; Tokyo, Japan.) For Caribbean/LatinAmerica, contact headquarters in Tacoma.

The product use recommendations in this publica-tion are based on APA – The Engineered WoodAssociation’s continuing programs of laboratorytesting, product research, and comprehensive fieldexperience. However, because the Association hasno control over quality of workmanship or the con-ditions under which engineered wood products areused, it cannot accept responsibility for productperformance or designs as actually constructed.Because engineered wood product performancerequirements vary geographically, consult yourlocal architect, engineer or design professional toassure compliance with code, construction, andperformance requirements.

Form No. W410B/Revised June 1999/0200

www.apawood.org@Web Address:

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oriented strand board

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