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size of roof sheathing

mikemjm | Posted in Construction Techniques on July 19, 2006 03:42am

I’m getting ready to do a roof and I’ve noticed a lot of the roofs in the area have “dips” between the rafters or trusses, which I would guess is from using too thin of a plywood or OSB sheathing. My addition will have trusses 24″ O.C. with a 8:12 pitch on the main roof and a 5.45:12 pitch on a shed dormer, both with asphalt shingles. I’m in the Mid-Atlantic region so snow load is a consideration, too. The lumberyard spec is for 7/16″ OSB. From everyone’s experience, is that sufficient or should I up the size to 1/2″ or even 9/16″? I’ll be using “H” clips between the trusses.

Thanks in advance for you input.

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  1. User avater
    hammer1 | Jul 19, 2006 05:10pm | #1

    Most of us use 7/16" OSB for wall sheathing. Every manufacturer of OSB, I've worked with, requires full support (blocking) on all edges of the 7/16" sheathing. We don't consider OSB to be a suitable choice for roof sheathing. H clips do not meet the edge support requirements. The better builders will only use 5/8" CDX plywood for roof sheathing, some use 1/2".

    Industry is always offering new products. Many builders use an OSB like product on floors, such as Advantech. This is a product that may look like ordinary OSB but is quite different. It's too heavy to handle on a roof and too expensive. There may be some new OSB roof sheathing products that I haven't used but ordinary wall sheathing would be a poor choice. The builders that use 7/16" OSB for roof sheathing are the ones to avoid.

    Beat it to fit / Paint it to match

  2. davidmeiland | Jul 19, 2006 05:16pm | #2

    I use 5/8" CDX plywood with H-clips. If it were available out here I might use 5/8" Advantech T&G.

    7/16" OSB on a roof would flex way too much under my weight. That's the bottom-of-the-barrel material to use for a roof deck.

  3. xosder11 | Jul 19, 2006 05:39pm | #3

    5/8" CDX Ply as a minimum for any roof. The clay tile roof we did on the last job used 3/4", as required by the roof tile manufacturer.

    1. mikemjm | Jul 19, 2006 06:37pm | #4

      That answers my question. 5/8" CDX plywood, at a minimum, appears to be the way to go. Thanks.

      1. JohnSprung | Jul 19, 2006 09:52pm | #5

        Why CDX?  Consider Struct #1, especially if wind or seismic considerations apply.  It can also be less expensive.  

         

        -- J.S.

         

      2. User avater
        BossHog | Jul 19, 2006 10:12pm | #6

        Around here 1/2" is pretty standard with roof trusses 2' O.C.I've never seen any of the dips you talk about.
        The first precept was never to accept a thing as true until I knew it as such without a single doubt. [Rene Descartes on scientific method]

  4. R-Squared | Jul 20, 2006 03:35am | #7

    If you don't want to see the rafters/trusses in a couple of years, don't put them 24" oc. The roof I just framed is 16" oc with 5/8 osb on it. In this case, I believe that slightly over building is worth every penny. I'm certain that knowone will look at that roof and say "who in the heck produced that mess." Good luck.

  5. MikeSmith | Jul 20, 2006 04:36am | #8

    mike... we used to use 1/2" when the framing was 16" oc

    and 5/8" when it was 24" oc ... in both cases we used  H-clips

    now we use only  5/8" Advantech  tongue & groove..

    this eliminates all the extra blocking requirements we have in our wind zone  ( 110 mph )

    there is also a product made by CanPly which is a  modern T&G in a 1/2" plywood

    if i could get that i would use that on any of our 16" OC framed roofs

    i might even use it on some of our 19.2" OC frames.. but i would continue to use the 5/8" on the 24" oc roofs

    Mike Smith Rhode Island : Design / Build / Repair / Restore

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