The problem with shiplap is that there is no tongue to bury into a groove. You could face nail the exposed part with finish nails and fill afterwards. The bottom part of the shiplap could also be finish nailed. The size would depend on what's between the wood and the joist.I am installing a shiplap ceiling in our kitchen. The shiplap is 10" wide, and we're going to fasten it directly to the floor joists. Does anyone have any advice on what to use for nails? Ideally, we'd love to have them not show. Thanks!