Old 11-25-07, 12:26 PM
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I'm using G-P 3/4" T&G OSB for underlayment for new carpet.
Does it matter which side goes up or down?
Normal printed specs, brand, etc. on one side, nothing on the other.
I thought I seen OSB somewhere that "THIS SIDE UP" or OUT was printed on one side.
Also two short grooves are cut into one end of sheet, approx.
1/2 x 1/2 x 3--4" in sheet, these are each 12" in on the same 4' end, and nothing on the other 4' end, anyone know their purpose??

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Old 11-28-07, 06:26 AM
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The shiny side of OSB always goes in or down. The 'rougher' side is more moisture resistant. While this is important on new construction I doubt it makes much difference when used in an already dry location.
Old 11-28-07, 02:55 PM
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I prefer using something like Advantech, since it has a certain water repelling property, and it is marked with dots on 16", 19.2" and 24" centers, making it alot easier to secure to your joisting. But like Marksr said, the slick side goes down. You can find out first hand the reason for this if you mistakenly place one upside down on a 4:12 pitch or greater roof.
Old 11-28-07, 05:36 PM
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I don't know the reasoning why, but if you use osb for siding [like a shed,barn] and you paint the slick side - pieces of wood willl peel off of the osb over time. Paint the rough side and it stays together.

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