OSB Oriented Strand Board Sheathing:

This article defines and illustrates the properties of OSB or oriented strand board roof or wall sheathing.

This article series describes wood products used in construction including engineered lumber, OSB, and Plywood products.

Page top photo: OSB exterior sheathing being applied to a Poughkeepsie, New York garage during reconstruction and repairs in 2011.

Definition & Characteristics of OSB - Oriented Strand Board

"OSB" or Oriented Strand Board wood products is similar to LVL and PSL, but OSB is produced in sheets (typically 4' x 8' in size) and is constructed of shorter strands of wood or even (in the case of 4' x 8' sheets) wood chips that may be roughly rectangular in shape.

Just above our photograph shows OSB subflooring. [Click to enlarge any image].

Developed in the 1980's, oriented strand board is an engineered wood product in which strands and flakes of wood are cut from straight, low-knot small-diameter logs, usually aspen or white birch.

The wood strands and flakes of OSB are glued (or "bonded") together with a phenol-formaldehyde resin binder (forming a waterproof glue), heated (to at least 120 degF), and are compressed and flattened using pressure.

Other chemical binders may be used in OSB products, and the OSB sheathing surface may have a wax coating to improve water resistance of the product.

Our photographs of OSB "plywood" below illustrate that the wood fragments glued together under heat and pressure are deliberately oriented randomly to produce greater strength than would be achieved if these small individual fragments were all oriented in the same direction

Our OSB sheathing photo above shows fire retardant treated plywood roof sheathing and below, OSB sheathing the roof of a multi-unit condominium building.

Notice that to meet fire codes, for one truss-bay adjacent to the firewall a fire retardant-treated FRT plywood was used in lieu of OSB.

Properties of OSB Panels & OSB Sheathing Ratings, Markings, Lumber Stamps

In an OSB panel the two exterior surface layers of wood strands are oriented parallel to the long axis of the panel. In the interior OSB panel layer or "core layer" strands are oriented either randomly or across the short axis of the OSB panel. In overall thickness the ratio of face panels to core panel ranges from 40:60 to 60:40.

According to the Universite Laval and also Timberco, the dimensions of wood strands used in OSB are specified in industry standards; most producers of OSB use a combination of strands that are up to 6" long and 1" wide or from another source, 19-40 mm in width and 90 to 100mm in length.

OSB is a modern wood product that developed from earlier 1970's "waferboard" product. In 1990 the Structural Board Association was formed. By 1996 there were 38 OSB producers in North America.

But unlike waferboard whose composite wood chips were place randomly, an oriented strand board product is made from wood chips that are deliberately oriented with respect to one another to provide greater strength.

As a result, modern OSB products are rated at the same strength as plywood products. OSB roofing panels are available with a perforated (breathable) foil radiant barrier affixed to the pane's interior surface.

Type Variations of OSB Specialty OSB Sheathing Products

Below: OSB for sale in a Home Depot web page in 2021

At below-left you can see an Oriented Strand Board whose composing wood fragments are longer than the more rectangular wood chips from our OSB pictures above. Still the strands are oriented randomly for strength.

Below is a cedar OSB product used in construction of cedar-lined closets, a less costly alternative to solid wood cedar planks traditionally used for that purpose.

Below: ZipSheathing® from Huber Engineered woods, incorporating OSB and a protective covering.

• ZIP SYSTEM® OSB SHEATHING MANUAL [PDF] Huber Engineered Woods 10925 David Taylor Drive Suite 300 Charlotte, NC 28262 1.800.933.9220
  
  This sheathing combines OSB with a protective overlay that eliminates need for a separate housewrap. A companion product, a sealing tape, is applied to sheathing joints. Retrieved 2019/09/11 original source: https://zipsystemrevolution.com/wp-content/uploads/2018/09/ZIP-System-Installation-Manual-HUB-81670-REV-8_18.pdf
  
  Excerpt: ZIP System® roof and wall sheathing panels are oriented strand board (OSB), wood structural panels with built-in protective overlays that eliminate the need for building wrap or roofing felt. Install the panels, tape the seams with ZIP System™ tape, and the building is rough dried-in.

Mold Growth on OSB Oriented Strand Board Products

Our moldy OSB roof and attic gable end wall sheathing photo (left) illustrates that as with most other wood products, if left exposed in a damp or wet environment, some species of mold will grow readily on this material.

Also see ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD, and because some indoor "black mold" on wood framing may be harmless cosmetic mold, also

see RECOGNIZE HARMLESS BLACK MOLD

Water Damaged OSB Sheathing

OSB, even OSB manufactured with waxes and preservatives intended to protect it from moisture, will in our experience ultimately show delamination or feathering or "frizzing" when left exposed to the weather.

In my OPINION superficial weathering like that shown above (at a VA hospital in New York) probably doesn't have a significant impact on the OSB sheathing's structural strength, but left exposed to moisure or weather for sufficent time we expect OSB, like other wood products, to become softened, damaged, and ultimately vulnerable to failure.

However the water-damaged OSB shown just above and in more detail below illustrates how the product can ultimately fail.

• Failures may occur as loss of connections to the structure if the OSB is softened around nails or construction screws.
• Failures may occur as point loads or fractures if water damaged OSB is, for example, in use as roof sheathing in an area subject to snow loads.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

I think I have been endangered or harmed by exposure to OSB (Oriented Strand Board) Sheathing

Do you know anywhere I can contact ? Because I was placed and subjected to a very harmful OSB BOARDS when I bought a home the HOA accused me of being in VIOLATIONS, not disclosed to me I placed all funds as my down payment on the home so I didn't want to be heavily fined by the HOA.

I find out later the DENIED SELLERS a PERMIT to have built a extra bedroom halfway wrong.

SELLERS ABANDONED HOME. I tried to do myself what HOA EXPECTED me and threatened me to finish and fix.

Unknowingly I had been getting extremely close to, and hammering next to, and painting it. OLD WEATHERED OSB BOARDS that pierced fine asbestos fibers and splinters everywhere in my flesh.

It's been over 3 years and it's still pouring and popping out of my skin including my entire FACE.
Pleading for anyone to help me.

All the DOCTORS at the ER HOSPITAL thinks I'm seeing things, and won't believe a word I say nor help me at all after 12 different visits the 1st by ambulance. On 2019-01-01 by Micky

by (mod) - Advice for reader frightened by OSB sheathing

OSB wafer board does not contain asbestos. And OSB wafer board is not a fiberboard product but rather is made of wood chips and glue.

Consulting the offical safety data sheets for OSB manufacturers will tell us that the primary potential health hazard from OSB sheathing would be breathing wood dust produced during sawing or similar operations.

It's important for you to find a doctor whom you trust, discuss your concerns and hospital visits and any tests you had done, and then listen to that doctor's advice.

I recommend reading about MORGELLONS SYNDROME

Details about OSB sheathing are found at SHEATHING, OSB and include OSB panel identification and ingredients.

Here are some example

SDS (Safety Data Sheets) for OSB Sheathing

• WEYERHAUSER ORIENTED STRAND BOARD (OSB) PRODUCT INFORMATION SDS [PDF] (2018) [Weyerhauser website]
  Weyerhaeuser, 20 Occidental Ave S., Seattle, WA 98104 E
  MERGENCY PHONE (DOT): (844) 523-4081 (3E Company)
  BUSINESS PHONE: (206) 539-3910
  
  Excerpt:
  TRADE NAME(S): Weyerhaeuser Oriented Strand Board (OSB) products including: Sheathing, Edge, Edge Gold™, RBS™ (Radiant Barrier Sheathing), Rim Board, SturdiStep™
  SYNONYMS and/or GRADES: Radiant Barrier Sheathing (RBS™), Rim Board, Web stock, Sheathing, Roof Sheathing
• LANBOARD OSB SDS [PDF] (2015) Langboard, Inc. P.O. Box 837 320 Langboard Lane Quitman, GA 31643 Telephone: (229) 263-8943
  
  Excerpt: OSB is produced with interlocking wood fibers having a slightly aromatic resinous odor and natural wood color. The wood component of these products may consist of alder, aspen, beech, birch, hickory, maple, oak, pecan, pine, poplar, western red cedar and/or other mixed hardwood species.
• West Fraser, NORBORD OSB BOARD (which includes OSB branded West Fraser) SDS [PDF] (2021) |
  
  Including these trade names: Sub-Floors & Stairs: Stabledge, TruFlor PointSIX, TrufFlorSub-Flooring, Pinnacle, Rimboard, Rimboard Plus, Durastrand PointSIX, SteadiTred, and T&G JAS. Wall Sheathing: TallWall, QuakeZone, Windstorm, JAS, Trubord Roof Sheathing: Solarbord, Trubord, and Square-Edge JAS. Industrial: TruDeck, StableDeck, StableDeckPlus, CoreDeckPlus, StableWall, StableRV, SipFacers, NorCore, Furnitures, SteadiPack, Web-Stock, and ShedDeck.
  
  Excerpt: POTENTIAL HEALTH EFFECTS: The wood panels in the purchase form do not represent a health hazard.
  
  The health effects mentioned below could happen if the board is mechanically processed, and dust particles (wood and polymerized resin) are generated in the environment.
  
  Inhalation of dust may cause irritation to upper respiratory system ...

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Continue reading at SHEATHING, PLYWOOD or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• DEFINITIONS of ENGINEERED WOOD OSB LVL etc
• PLYWOOD Roof, Wall, Floor Decks & Sheathing
• SHEATHING, FIBERBOARD
• SHEATHING, GYPSUM BOARD
• SHEATHING, OSB
• SHEATHING, PLYWOOD
• SHEATHING, EXTERIOR PRODUCT INDEX
• SIDING, FIBER CEMENT IDENTIFICATION - identify fiber cement siding products
• SIDING HARDBOARD IDENTIFICATION & CLAIMS - home - wood-fiber based siding products
• STRESS SKIN / STRUCTURAL INSULATED PANELS (SIPs)

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SHEATHING, OSB at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING STRUCTURES

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