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Old 08-26-2010, 08:26 PM   #1
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Replacing some of roof the sheathing


I will be replacing some of the sheathing to add a cross gable. The existing stuff is 3/8" plywood. If I used the more common OSB to replace sections, it comes in 7/16". Is there any issue in using these two different thicknesses of sheathing on the same slope. Would the 1/16" difference be a problem with getting the asphalt shingles to lay flat?

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Old 08-26-2010, 08:41 PM   #2
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Replacing some of roof the sheathing


Can you afford to replace the whole sheathing? 3/8 is just crap anyway.

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Old 08-26-2010, 09:12 PM   #3
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Replacing some of roof the sheathing


instead of sheathing can you use a ice/water shield??
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Old 08-26-2010, 09:24 PM   #4
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Replacing some of roof the sheathing


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Originally Posted by tns1 View Post
I will be replacing some of the sheathing to add a cross gable. The existing stuff is 3/8" plywood. If I used the more common OSB to replace sections, it comes in 7/16". Is there any issue in using these two different thicknesses of sheathing on the same slope. Would the 1/16" difference be a problem with getting the asphalt shingles to lay flat?
Only in the worst case scenario if the plywood has shrunk a little and the OSB has been wet and swollen. Even then, a little minor shimming (using a couple of layers of felt paper) will make sure the thickness difference doesn't telegraph.
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Old 08-26-2010, 11:14 PM   #5
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Replacing some of roof the sheathing


the 1/16" will not make a difference.
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Old 08-27-2010, 11:26 AM   #6
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Replacing some of roof the sheathing


"Sheathing less than 1/2“ in thickness placed over rafters which are spaced more than 20” on center require
plywood clips or blocked edges. Typically 7/16” OSB with a span rating of 24/16 is used and will not require
clips. (Table R503.2.1(1))" Be sure to support the old 3/8 at it's edges.

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Old 08-27-2010, 07:27 PM   #7
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Replacing some of roof the sheathing


Yes, the existing 3/8" panels do have aluminum clips along the edges between rafters. These same clips would probably not work if 7/16" and 3/8" were butted together. I suppose blocking would be needed in that case.
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Old 09-18-2010, 11:47 PM   #8
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Replacing some of roof the sheathing


With the huge price difference between osb and acx, I would think that some manufacturer would make osb with some kind of weatherproof smooth face that would make it acceptable for use on open eaves and other visible uses.

Is there such a thing?
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Old 09-20-2010, 12:17 AM   #9
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Replacing some of roof the sheathing


i would use the clips on 7/16 osb, they are only $5 per 100, simple, cheap and extra strength. i totally see where you're coming from though. prices on osb are so good now you could literally double it up for the same as 1/2 cdx
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Old 09-20-2010, 05:25 PM   #10
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Replacing some of roof the sheathing


Yeah, seems like they could either sand one face or add some kind of thin laminate that paint would stick to, adding no more than a couple bucks to the cost. I think plywood is going the way of the dodo. osb or something like it will have to fill the gap.

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