Every stepped and every staggered gable abutment must be so constructed to prevent rainwater and dampness from penetrating below the abutting roof line. This is because the external skin changes status below the roof line and becomes an internal skin. The system fulfils three basic requirements: It prevents dampness from penetrating below the critical stepped roof line. It externally weatherproofs and flashes the physical roof/masonry intersection. It also prevents the inside skin from becoming damp.