A.Cedar gains and loses moisture readily, resulting in board swelling and shrinkage. The high initial moisture content of some of the currently available cedar may contribute to this problem.
Because of this tendency, proper nailing, with just one nail per clapboard at each stud, is essential, whether or not the siding is installed over foam insulation. The nail must not penetrate the board below it. Instead, the clapboard above must hold the top of the clapboard below it with friction. If there is more than one nail across the width...
to read the full article.