Plywood

[Juan L]

I’m building a wood shed in my backyard and I’m using exterior grade plywood for the flooring and sheathing. Do I need to leave some gap in between sheets for plywood expansion?

[Henry in MI]

Juan, because of the way that the plies run at 90 degrees to the adjoining plies, plywood does not expand the way solid wood does. The glue between the plies holds the wood from moving but there is a slight thickening with the changes in moisture/humidity. You can butt one sheet up to the next one and, in fact, the plywood that comes milled with tongue and groove joints on the edges show that this is acceptable.

Henry in MI

[tomh]

Most plywood manufacturers recommend spacing sheets 1/8″ to prevent buckling. The tounge and groove sheets are self-spacing and slide over each other, but full flat sheets need to be spaced. I usually use a 10 penny nail to get the recommended space between sheets. The roof sheets are most suseptible to some swelling. Failure to leave a small gap can lead to a wavy appearance, but is probably not structurally important.

If you search the words – plywood expansion gap – on the web you will find numerous references to this requirement. Most roof and floor sheeting is sized slightly smaller than 4’x8′ and has the gap requirement stamped on the back.

[Author]

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