Antisiphon lap joint for building sheets

摘要

A building sheet suitable for roofing and siding provides a weatherproof lap joint having an antisiphon gap when installed partially overlapping an adjacent like building sheet by spacing the entire overlapping portion of one sheet above the lapped portion of an adjacent sheet. Parallel strengthening ribs formed into the building sheet are structurally modified along one edge to form an overlapping member and along the opposite edge to form a lapped member. The overlapping member includes an intermediate strengthening bead and an exterior downwardly projecting sealing lip which rests upon the lapped member of an adjacent sheet and spaces the entire overlapping member of one sheet above the lapped member of the adjacent sheet. The force created by fasteners securing the flat portions of the sheets to the underlying structure is transferred through the overlapping member, due to its being entirely separated from the lapped member, and focuses downward pressure at the sealing lip causing it to resiliently deform and achieve a tight seal while maintaining the antisiphon gap. Low sills, alternating in a parallel array with the ribs, add strength to the sheet, as does the bead incorporated into the margin of the overlapping member and a small angled fastening flange along the edge of the lapped member which also provide additional rigidity to these edges.