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SonnyB
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# Posted: 2 Oct 2012 05:40pm
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Is it ok to use 1/2" BC plywood for my roof sheathing if my rafters are 2' OC? I know that 7/16 OSB will flex way too much. I am building a 20x32 1 1/2 story with lofts on both sides. I am going to install metal roofing. Thanks for your help!
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MtnDon
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# Posted: 2 Oct 2012 06:43pm
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The plywood / OSB will be stamped with the specs for what it will span. 7/16 OSB usually is approved for 24", but that is the bare minimum for a roof. 5/8 is better as would be 16 inch OC. The 1/2 BC ply does not have an X so may or may not be approved for that use. (X = exterior glues) Read the stamps.
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toyota_mdt_tech
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# Posted: 3 Oct 2012 10:52am
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All new contruction in my area uses 1/2" OSB over trusses spanning 24", but your snow load may vary. They do use plywood on the overhand so looking up, you dont see the strandboard. Not an issue if you enclose the soffits. Lay yourt sheets horizontally and stager them like bricks. Use the H clips between rows.
I didnt use a single sheet of OSB on my cabin. I hate the stuff, it gets wet from a leak etc, it swells up to twice its size and comes apart.
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SonnyB
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# Posted: 3 Oct 2012 05:46pm
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I looked at the 1/2 bc today and it has a stamp that states "Exterior". But I just checked prices and its $26 a sheet!!
Ready to start tusses this weekend. Pre cutting them now but not really sure which way I want to go with the sheathing.
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SonnyB
Member
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# Posted: 3 Oct 2012 05:55pm
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Just called HD and they have 5/8" OSB for $15.50 a sheet so might go that direction with trusses 2'oc, titanium fabric and metal roof on top of that!
What you think?
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toyota_mdt_tech
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# Posted: 3 Oct 2012 06:39pm - Edited by: toyota_mdt_tech
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Well, $10 per sheet difference. You can use probably 1/2". I covered mine with 30lb felt, then had the metal roofing installed over that (sub'd it out to pro roofers)
If you ever get a leak, a tree branch and you not there, pokes a hole, it gets wet with OSB, its going to be a big job to fix it. How many sheets will you need. Where are you located. What size cabin/roof/pitch.
If its 12 sheets (for example) , $10 diff per sheet, you are looking at $120 total.
Not much in the overall build.
I built when wood was cheap. There was a glut of timber products. I paid $11 per sheet for 1/2". I did pay about $28 per sheet for my 5/8" T1-11, but its the plywood type, not strandboard. Cheap by todays prices also.
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MtnDon
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# Posted: 3 Oct 2012 06:41pm - Edited by: MtnDon
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5/8 at 15.50 is a good deal right now; go for it. It's almost $20 here in NM today. Then the Titanium underlayment and metal.
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johng
Member
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# Posted: 3 Oct 2012 07:52pm - Edited by: johng
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BC plywood has a sanded side and a rough side. CD plywood (sheathing) has a rough side and a rougher side.
If using OSB, I wouldn't use less than 19/32 on 2 foot centers. Currently 4 ply 15/32 CD is close enough in price so that would be my choice.
There is no reason for BC plywood for roof sheathing unless the underside would be exposed to view, thus putting the "B" side down.
However if you are installing shingles you would see all the nails poking through making it a huge waste of money.
All of the above are made with exterior glue, but the smooth sanded surface of the "B"C plywood is the only one rated to shed surface water.
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