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Plywood vs. OSB (Oriented Strand Board) | Differences & Applications

Plywood vs. OSB (Oriented Strand Board) | Differences & Applications

by Fred Fauth (email Fred) | | July 3, 2009 | 25 Comments »

Reader Question: What is the difference between plywood and oriented strand board (OSB)?  What are the appropriate uses for each? Is one better than the other for new home construction? — John

John, those are great questions.  Here’s the basic rundown on each material and suitable applications.

Plywood

Plywood is made by cutting thin layers of a tree all the way around its circumference.  These boards are then laminated together using a hot press (basically a giant iron that fuses wood and glue together under heat). The first piece of wood is placed so that it rolls “up” while each subsequent layer is laid 90 degrees to the one below it, and upside-down. The result is that the tendency for the boards to warp into their original shape is diminished as each board is pressed against the other layers. As a result, thicker plywood (say, 5/8″ and above, which is made from 5 or more plies) is much less likely to warp than thinner plywood, such as 1/4″ or 3/8″.

plywood

All plywood will still have some warp, especially because some layers have greater warp tendency than others (for instance, layers derived closer to the center of the tree).  Obviously, these forces are easily overcome by fasteners when the plywood is attached to studs or joists.

When exposed to water, over time plywood will delaminate.  It is important to avoid an extensive amount of water exposure during construction.  (Some water, however, will not damage the boards). We’ve had a number of readers ask about water exposure. The reality is that water and plywood don’t mix well, especially over time. If you leave plywood exposed to water, it will eventually rot and must be replaced.

Plywood is sold in nominal thicknesses, such as 3/4″. However, finished plywood is actually 1/32″ thinner than its nominal rating. For example, 3/4″ plywood is actually 23/32″ thick. The nominal length of plywood is true to its actual length (4′ x 8′ sheets are usually 4′ x 8′); however, even length and width can vary slightly due to imprecise cutting.

Oriented Strand Board (OSB)

OSB is built by pressing smallers strands of wood together with glue and wax in a hot press.  OSB looks a lot like a collage of different wood chips. Unlike it’s plywood counterpart, OSB lacks the forces that tend the wood to warp, and so is easier to get perfect dimensions and avoid warping tendencies.

osb

The one major disadvantage of OSB is its propensity to expand with moisture.  The edges of OSB will dramatically expand (>15%) when wet, and takes much longer to return to normal size.  If the moisture is allowed to remain in the OSB for some time, the boards may never return to their original dimensions.  The effects of water on OSB are much worse than plywood, although in both cases water and moisture should be avoided.

Applications for Plywood vs. OSB

Subflooring

When used as a subfloor, either product will work for many flooring surfaces, especially carpet where there will be no noticeable difference. For hardwoods, plywood is desirable because it holds nails slightly better than OSB.  Also, since the entire floor will be built with the same product, some care should be taken in deciding whether its worth it to risk potential moisture in bathrooms and kitchens that could cause OSB sub- flooring to buckle and rise at the joints.  For ceramic and stone tiles, either can be used as long as the product meets the deflection requirements of the installation.

Here’s an article using plywood and shingles to level a subfloor that may be of interest.

Roofing

For roofs, plywood is preferable and required by code in many states.  Since roofing wood will be exposure to moisture, OSB will have a tendency to expand and warp which will both weaken the roof and may pry up the shingles, making any leak problem worse. However, for exterior buildings, such as sheds, OSB is an appropriate product.

Here’s an example of building a shed that uses OSB and Advantech, a material mentioned in the comments section below.

Sheathing

For wall sheating, OSB or plywood is acceptable, but again, plywood is preferable unless extreme cost savings is a concern.

Cost Savings for OSB vs. Plywood

The cost savings of OSB over plywood will be less than 2% of the total cost of most homes.  If we were building a new home, we’d choose plywood given only these two choices.  That said, Plywood and OSB aren’t your only options.  Our buddy Todd over at Home Construction Improvement swears by Advantech Sheathing, a next-generation surface that resists moisture much better than either plywood or OSB.  He built his whole house with it!

(Photos: nieve44/laluz, hryck)

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25 Responses to Plywood vs. OSB (Oriented Strand Board) | Differences & Applications

  • Todd responds...
    July 3rd, 2009 2:43 pm

    Fred,

    Couple things worth pointing out. The layers of plywood are oriented with the grain 90 degrees from the previous layer for another really important reason. Plywood panels give floors, walls and roofs substantial shear strength to counter wind and other horizontal forces such as earthquakes. By orienting the grain in two directions you create a much stronger “panel”. The same theory applies to OSB and that’s why the wafers are allowed to be dispersed in many different directions.

    Also, most all OSB products are now approved for construction of walls, floors and roofs. All of these products have made significant improvements when it comes to strength with fasteners. OSB also happens to be quite earth friendly as it can be manufactured with new growth wood instead of old growth.

    Great post Fred! Some of us take for granted the differences between these products.

    [Reply]

  • Fred responds...
    July 5th, 2009 11:18 pm

    Todd, great additions… always appreciated.

    I’m still skeptical on OSB applications where water is involved. I have seen that stuff swell to a ridiculous degree (must more than 15%). Would like to see some demonstrations where OSB is subjected to a lot of moisture over several years, or where a leak develops on the edges.

    [Reply]

  • Alice Soininen responds...
    July 27th, 2009 9:07 am

    We built a gorgeous timberframe home in northern VT ten years ago. When our builder came to replace a cracked clapboard, he discovered that the OSB on theentire south and west exposures of our home was wet and rotten. The apparent cause was a buildup of moisture beneath the Typar (due to condensation???). We are having to scrape off the OSB surface of the stress skin panels (manufactured by Foard in Brattleboro, VT) and re-glue a new surface to the panels prior to putting on a siding. We are very discouraged as this is a $70K problem covered by only 10K of “mold and wet/dry rot” insurance. Also, we do not want to have a repeat of the same problem. Solution??

    [Reply]

    Elaine Reply:

    We had a snow and ice storm last Jan. 2011. It caused an ice dam on the roof. We replaced the roof that was damaged. Insurance wouldn’t cover it. Now 1 year later we have mold inside the house on the wall. We took off the vinyl siding on the outside of where the mold was. The osb was wet and rotten. We think this is from the ice dam one year earlier. How long does it take wood to rot? Where we took the siding off there is no sunlight.

    [Reply]

    Fred Reply:

    Wood can start to rot in as little as a few weeks if exposed to constant moisture. OSB, particularly will delaminate in these conditions. From what you describe, you’ve got a problem that is several months in the making.

    [Reply]

    Greg Bublitz Reply:

    It sounds like the problem you are having is related to moisture infiltration rather than the 1 year old ice dam problem. If your vinyl siding is not properly installed (proper vapor retarder – Tyvek, and proper flashing and waterproofing practices) it will allow water to reach the substrate. This is not a problem of what your wall is sheathed with, it is a problem of poor installation of your siding. All siding leaks. Could also have to do with improper roof flashings.

    [Reply]

  • Phil responds...
    December 8th, 2009 12:22 pm

    I have 5/8th inch plywood subfloor in my house that I am laying 3/4 inch hardwood flooring over. I have to build up my family room with 1/4 inch luan to match the level of my kitchen. Am considering using 1/4 inch OSB due to cost, but don’t want to sacrifice quality. Anybody have an opinion about the appropriateness of OSB for this application?

    [Reply]

    Fred Reply:

    I think it’s perfectly fine for you to use OSB in the application you describe. This article may also be of some interest to you:

    http://www.oneprojectcloser.com/how-to-level-a-plywood-or-osb-subfloor-using-asphalt-shingles-construction-felt/

    Fred

    [Reply]

  • Wieslaw Zielinski responds...
    August 31st, 2010 9:44 am

    In my kitchen is 3/4″plywood floor.Can I use 1/2″ OSB boards over 3/4″ plywood to build subfloor for ceramic tiles?

    [Reply]

  • Roberto luis responds...
    November 20th, 2010 7:32 pm

    I have osb as sub floor and I want to put solid hard wood flooring and nailed is this posible

    [Reply]

  • Fred responds...
    November 22nd, 2010 7:20 pm

    Roberto, yes this is possible, but a lot of factors should be considered: how thick is the OSB? Are you laying the hardwoods perpendicular or parallel to the joists? What type of hardwood do you plan to lay?

    [Reply]

  • steve Levette responds...
    December 8th, 2010 2:38 pm

    Hi, I have a new garage and I have moisture proof sheetrock on the walls. I like the finished look of OSB board. Can I install OSB board over the sheetrock? Is this a good idea? Thanks Steve

    [Reply]

    Fred Reply:

    Steve, I’m confused. You want the walls to look like OSB rather than drywall? That’s pretty unusual…. Why would you want that?

    [Reply]

  • Jean Revaul responds...
    November 4th, 2011 1:07 pm

    My husband decided to store some leftover OSB in the barn stacked against a wall.
    We have two young geldings and they have eaten the OSB on a regular basis and seem to do pretty good on it. One horse has really gained weight on it.

    It started with the feeder my husband built out of the OSB. This was not intentional on our part, but what is in that stuff that makes a horse eat it wood chips and all? They get hay and grain everyday but if there is a board in there, they eat that too!! Would plywood be better? Maybe they would not eat that??

    [Reply]

    Fred Reply:

    Jean, I can honestly say I have no idea!

    [Reply]

  • Vaibhav responds...
    March 1st, 2012 4:31 pm

    I’m getting vinyl in one of my rooms at this ment and though they were supposed to get the 1/4 inch luan what they are applying is actually more like 3/16 and am being told that’s what’s called 1/4 in construction terms. Is that true?

    [Reply]

    Fred Reply:

    Actually, 1/4″ luan is normally finished to 7/32, but it could be easily mistaken for 3/16 if you’re thinking that it should be exactly 1/4. I think they are telling you the truth.

    [Reply]

  • Andrew Young responds...
    July 28th, 2012 10:02 am

    May OSB boards (panels) be use for open (no awning, canopy or roof above it) outdoor deck ? Deck eventually will be covered by outdoor carpet.

    If yes, what kind of OSB should be use ?
    Andrew

    [Reply]

  • richard responds...
    August 30th, 2012 5:13 pm

    i have osb used as a facia / decorative band around an outdoors deck. the problem is that the edge of the osb has been exposed to the elements for seven years. the edge was painted, but have deteriorated.

    any suggestions on preventing further deterioration.

    another unrelated question: how well do screws work on osb?

    [Reply]

  • Vince responds...
    October 13th, 2012 10:04 pm

    I am working on a old complex apartment with subfroors and on the kitchen and restroom iam installing 1 1/8 OSB

    [Reply]

  • Juan J. Mascorro responds...
    October 19th, 2012 4:57 pm

    I’m a Code Enforcement officer for the City of Holland, MI 49423. One of my duties it to enforce the Minimum Housing-Property Maintenance Code for rentals. Recently I have called the removal and replacement of floor covering in certain rooms in a rental dwelling. The LL/owner has removed the floor covering and in many cases has laid down OSB Board sheets. He has his maintenance people glue and secure it down with fasteners. Instead of placing carperting, tiles or linoleum down they stain then OSB floor boards, seal it with a lacquer finish and call it done. The question is is this an approved method and application and use of OSB boards as a finished floor. They do not use the OSB in kitchens or bathroom but every other room when called on. One of my co-workers thinks that this is not an approved method and use of OSB. I think if the OSB board is properly secured to the existing floor, proerly sealed at all joints and sealed with a hard durable lacquer finish it is acceptable. What are your thoughts and recommendations.

    Sincerely,

    Juan J. Mascorro

    [Reply]

  • Shawn responds...
    March 31st, 2013 8:54 pm

    I am having a house built. The builder left the osb out in the winter for three months. He is now using it on the floor, walls and roof. I paid extra for plywood. Should I be concerned that the wood was left uncovered in the winter for three months in the snow?

    [Reply]

    Fred Reply:

    I would be more concerned if you paid extra for plywood and he’s installing OSB! There’s no problem with the wood if it hasn’t absorbed moisture. You should be able to tell pretty easily whether the wood has been damaged. I assume that the OSB was at least covered, in a stack?

    [Reply]

  • Michelle responds...
    June 12th, 2013 4:13 pm

    We are having pull down attic stairs installed to utilize the attic as storage space. Our contractor was going to lay down some OSB instead of plywood as the flooring. Do you think one material would be preferential over the other in this case?

    [Reply]

  • rob responds...
    July 27th, 2013 7:43 pm

    Hey, I’m building a spring floor for my martial arts studio I’m opening. I’m trying to keep to a budget, but I’m not sure whether OSB will be the correct wood. The floor is going to be 42′ by 22′ it will consist of either 1/2 inch OSB or ply wood placed on top of high density foam blocks. Another 1/2 inch layer of wood will then be placed on top perpendicular to the originals. My main worry with OSB is whether it will be strong enough to support the impact of falls over time. I’m also slightly worried about the moisture problem OSB has. I’m going to have puzzle mats on top of the spring floor, but there is still a risk of a little sweat getting on the boards. One last note is the floor will be on top of concrete. Any help is greatly appreciated. Thank you!

    [Reply]





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