Board on board application is installed vertically with boards secured with gaps between and then boards secured over the gaps and overlapping the first boards very similar to board & bat except that the top boards are generally wider than bats which allows for more variety in the appearance of the finished product; both boards can be the same width or the bottom boards could be narrow with wide top boards wide or vise versa; it can even be applied with random width boards for lots of variety or with bottom boards 2" wider than top boards so that the reveal is the same width as the top board for a very symmetrical look.