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.
Our page to photo shows OSB oriented strand board used for roof decking, and at left our photograph shows OSB subflooring. [Click any image to see an enlarged, detailed version]
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 second OSB sheathing photo (above right) shows fire retardant treated plywood roof sheathing (below) and OSB roof decking (photo below at right in the image) sheathing the roof of a multi-unit condominium building.
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
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.
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.
Our main website topics listed at page top or at the MORE READING links at the bottom of this article provide in-depth, un-biased, expert information on building defect inspection, diagnosis, & repair.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Ask a Question or Search InspectApedia
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: email@example.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - firstname.lastname@example.org. Mr. Hankey is a frequent contributor to InspectAPedia.com.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones