The following advice came to me with the very best of intensions, but you know what they say about good intentions! On a recent store visit I overheard a staff member telling their customer to install ply clips (sometimes called H-clips) along the 4’ panel edges of the roof sheathing in order to create the required 1/8” panel spacing. That is a really bad idea! At each clip along the 4’ edge, a little “bump” is created that will most likely be visible from the street.
Clips installed on the 4’ sit on the rafter/truss and they will raise the panel sit slightly instead of allowing it to lie flush with the rafter/truss surface where it should be. Now fastening the panel means trying to force the panel to conform over the top of the clips and back down to the rafter/truss surface. This will be resisted by the engineered strength built into the panel. Fasteners spaced at 6”oc make conforming virtually impossible and will result in a ‘wavy’ effect along every 4’ joint.
You can solve the problem by temporarily placing a couple of 10d nails at 4’ ends to create the required 1/8” space, install the next panel, remove the 10d nails and put them on the next 4’ end – simple and easy!
All structural sheathing requires 1/8” spacing to allow for expansion with changes in moisture conditions. Installing clips along the 8’ is great (and may be required) because they are placed between the rafter/trusses to strengthen edges and create the required 1/8” spacing.