Abstract: Door jamb assemblies, and corresponding door assemblies, having elongate inserts received in cavities in corresponding jambs of the door assemblies. Structure and positioning of the insert acts to add stiffness to the jamb assembly. The jamb assembly is readily attached to a framing member of a building such that the jamb assembly moves in unison with movement of the building. Spacing blocks are preferably inserted into the cavity in the jamb, between the jamb face plate and the insert, such that the spacing blocks provide a collective mounting surface which receives the insert. When the door assembly is mounted using fasteners of the invention, further manipulation of the head of the fastener is ineffective to remove the door assembly from the building.