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Old 11-25-2009, 02:04 PM   #1
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OSB expansion

I recently lined the inside of my work shop with 7/16 osb, walls and ceiling.
Being quite anal I made sure every joint was tight as well as were the walls met the ceiling. My question now is , now that I'm done, how much will osb expand and contract?


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Old 11-25-2009, 02:21 PM   #2
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There are different grades of osb. I believe most of it is rated esposure grade 1, meaning it is suitable for use in damp environments, but not designed for immersion in water. OSB for sheathing is typically installed with 1/8 inch gaps between boards, presumably on the theory that the boards might get wet.

As for long term expansion contraction, OSB is an engineered wood product, so the individual fibers would typically expand and contract between 1 and 2 percent as they cycle between minimum and maximum moisture content. If your basement remains at roughly the same humidity level all year, you will not experience any movement. If the humidity level changes over the course of a year, the movement would likely be less than the 1 to 2 percent typical of wood, since there is so much glue in osb.


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Old 11-25-2009, 02:59 PM   #3
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"I recently lined the inside of my work shop with 7/16 osb, walls and ceiling." ------- If outside where it rains a lot and there is no heat, I would be concerned. The rating, as Daniel said: http://osbguide.tecotested.com/pdfs/en/el812.pdf

Compared to plywood: http://www.gp.com/build/PageViewer.a...elementid=6132

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Old 11-26-2009, 10:04 PM   #4
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osb blues

that's a good question. maybe for good measure, use a penny as a spacer next time, but by all means keep it off the floor at least a 1/4 inch. osb does not like moisture as it's thickness expands. iv'e never seen it buckle though, it just puffs up when it gets wet. wood cells are elongated, like rice. when wood gets wet it gets fatter but it never gets longer. maybe wood is like people, when we over eat we get fatter but we never get taller from it. maybe that's why osb doesn't seem to change much in height or width, just in it's thickness as the strands are placed every which way and when they do expand, it's just gets fatter. mdf (medium density fiberboard) is something to avoid in high humidity areas. if you wanna have a good laugh, or cry, use mdf in a basement. been there, done that. good question though.
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Old 12-16-2009, 01:14 AM   #5
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OSB expands at different rates across the panel as it is a hodge podge of wood and glue. With plywood any swelling from moisture is uniform which is why it is preferred for subflooring. For an interior application OSB should be fine as it is not likely to absorb much ambient moisture and I expect you plan to paint it. Sheetrock is commonly used and in high humidity situations it is going to cause a lot more problems with absorption than any wood product.
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expandtion , osb

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