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Thread: Plywood or OSB?

  1. #1
    Join Date
    Nov 2004
    Atlanta, Ga. burbs
    I have an outbuilding at the house we are buying. It used to be a pavilion for the company who bought the land many many moons ago.

    Anyway the shingles are in really bad shape. The pavilion is so old the decking looks like 1x6s. I would guess pre-plywood. Instead of replacing the rotten 1x6 with 1x6s for the decking I thought I would either use plywood or OSB, felt then shingle.

    Which is the question of the day for me.

    Would you use OSB or plywood decking? OSB is about 3 dollars per sheet cheaper than plywood. My calculations is I will need at least 50 sheets of whatever. (plywood is 150 bucks more + sales tax). If OSB do I need to get a particular color coded sheet? The OSB Home Depot had (smaller store) had one color coded yellow. They did not know the answer.

  2. #2
    Join Date
    Feb 2003
    S.W. PA
    OSB will work fine for roofing I would recommend 7/16 or thicker AS LONG AS the bottom will not be open to weather if it is set up so that it is open than cdx plywood will last longer

    OSB will still work if it is an open setup but MAY NOT last as long as the shingles

    If you go with ply wood use cdx because the glue used in it is made for exterior applications

  3. #3
    Join Date
    Oct 2004
    OSB is not directional, so you can turn it any direction.
    You can't do that with plywood, as it needs to bias the supporting rafters. Aslo, plywood tends to have hollow spots & voids.

    Plywood is a little friendlier to cut, but OSB would be my choice, due to less waste.

    OSB does have a slippery side, though.
    Install it smooth side down.

    I am not aware of any color coding for OSB.

    [Edited by bwal2 on 08-26-2005 at 01:46 AM]

  4. #4
    Join Date
    Feb 2003
    S.W. PA
    Originally posted by bwal2

    I am not aware of any color coding for OSB.

    home depot and lowes color code all their plywood and osb so cashiers know what to charge

  5. #5
    Join Date
    May 2004
    Seth: a couple comments..

    Some osb is directional, some isn't. Look at the rating stamp to be sure. If there's a double-arrow logo, pay attention to how it goes in. As somebody else said, smooth side goes down, and the arrows go across the trusses.

    Also, get yourself a big box of the simpson clips.

    As far as I know, there's no color code. What you're looking for is a stamp that says "24/16" or something like that. The first number is how wide a span you can use it for in a roof (truss spacing), and the second number is the max joist spacing if you want to use it for a floor.

    You now know everything that I do about osb.

    "If I had my life to live over again, I'd be a KA." - Albert Einstein

    It's later than you think.

  6. #6
    OSB, rough side up.

    If you're not using 5/8, 3/4 you need to use clips to support inbetween the trusses.

  7. #7
    Join Date
    Feb 2005
    Dothan, Al
    I was taught ( by an old man ) that osb handles moisture better than plywood - thats why I use osb on closet installs, attics under drain pan etc., instead of plywood.
    Ya'll correct me if this is wrong.


  8. #8
    Join Date
    Aug 2003
    Fort Worth, TX
    OSB is OK for roof decking, with a few caveats.

    First, roger on the Simpson clips. Do NOT butt joint the horizontal seams when you deck the roof. Not a bad idea to leave a small gap between the vertical seams, either.

    Secondly, stagger the vertical seams, do not allow one vertical seam to go from eave to ridge on a rafter.

    Thirdly, do the best you can to not allow the decking to get rained on before it gets felted and shingled. Ever drive by a tract home division on a sunny day and looking at the roof you can see where all the OSB under the shingles meet? That's the result of a combination of poor spacing between sheets and letting the stuff get rained on prior to roofing materials. This stuff will swell BIG TIME when wet.

    Lastly, as a safety note, if you do any trimming of sheets up on the roof (such as for roof jacks, vents, etc.) sweep off the sawdust right away. Sawdust on OSB is like ice. I kept a broom up with me when I was decking my shop just so I wouldn't end up on the ground.
    Building Physics Rule #1: Hot flows to cold.

    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure

    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

  9. #9
    Join Date
    Dec 2002
    in a house, Appomattox, Va.
    I would prefer plywood, myself. OSB dones not seem to hold up as well as plywood from what I've seem, and it does bloat up, that's why it comes coated in wax now- to keep rainwater from damaging it in one rain.

    Wouldn;t use the thinnest you can get on a roof, the thin stuff, ply or osb, seems to buckle in a few years and the roof has bows and waves all in it.

    I've seen plywood that rotted before the glue let go, and osb that became weak as cardboard when wet for 24 hrs.
    The phenolic based plywwod glue will give very good service- 50/60s homes had fir plywood with that glue for the soffet work and redwood fascia, still plenty solid after 40 yrs.
    Col 3:23

    questions asked, answers received, ignorance abated

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