T1-11 shiplap edge and Z-flashing — why a 48-inch sheet covers ~47.5 inches
The shiplap edge overlaps, so a 48″ sheet nets ~47.5″. Every horizontal butt joint gets Z-flashing, with the upper panel lapping over it.
What this diagram shows
Two details of T1-11 plywood panel siding. A plan section shows two panels interlocking at their rabbeted shiplap edges, so a 48-inch nominal sheet nets about 47.5 inches of coverage — the net width that sets the column count. A vertical section shows a horizontal butt joint where Z-flashing sits on the lower panel and the upper panel laps over its vertical leg, so water sheds out over the joint rather than behind it.
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T1-11 Siding Calculator
Free T1-11 siding calculator — 4x8/4x9 plywood/OSB panel sheets by shiplap-edge layout, with Z-flashing at horizontal joints, trim and siding nails.
