Window flashing is a system of materials — sill pan, flexible flashing tape, and integration with the wall’s water-resistive barrier — that directs any water infiltrating around the window frame to drain to the exterior of the wall rather than into the wall cavity and framing. The ASTM E2112 installation standard defines the correct sequence: (1) sill pan flashing with end dams, sloped outward; (2) water-resistive barrier (housewrap) lapped over the top of the sill pan; (3) flexible flashing tape up the jambs, lapped under the housewrap at the wall sides; (4) flexible tape and formed metal drip cap at the head, with housewrap lapped over the top. The critical failure mode: flexible tape applied over the housewrap at the jambs rather than under it — a sequence that creates a water dam directing moisture into the wall cavity rather than out. A misflashed window may perform acceptably for 3–7 years while the housewrap compensates, then suddenly reveal soft framing, degraded insulation, and interior moisture damage that requires opening the wall to repair. RainFire Builders trains every installation crew on ASTM E2112 sequence and supervisors verify the flashing at every opening before any siding is applied.