disclosed herein are embodiments of foam backing panels for use with lap siding and configured for mounting on a building . also disclosed are lap siding assemblies and products of lap sidings . one such embodiment of the foam backing panel comprises a rear face configured to contact the building , a front face configured for attachment to the lap siding , alignment means for aligning the lap siding relative to the building , means for providing a shadow line , opposing vertical side edges , a top face extending between a top edge of the front face and rear face and a bottom face extending between a bottom edge of the front face and rear face .