The APA American Plywood Association, has a series of “builder Tips” on their website. An important one is to remember to space your plywood panels to allow for expansion and contraction. If the seams are tight against each other, a buckled deck is usually the result when it expands with moisture.
APA recommends a 1/8-inch space between panel edge and end joints. Plywood and oriented strand board (OSB), like all wood products, will expand or shrink slightly with changes in moisture content. If the wood structural panels are tightly butted, there is no room for expansion and buckling can occur. That can mean costly, time-consuming callbacks. To assure best performance, follow these panel spacing and nailing recommendations for APA Rated Sheathing, APA Rated Sturd-I-Floor®, and APA Rated Siding.
Spacing Hint: Use a 10d box nail to gauge 1/8-inch spacing between panels. Spacer-type panel edge clips may also be used for roof sheathing applications.
Read More here http://www.apawood.org/buildertips/pages/M300.html