Window pan flashing detail: sloped sill, back dam, sealed corners, integrated with WRB

Description

BASC documents the window pan-flashing detail in step-by-step depth: install the WRB cut + folded to expose the rough opening; install a sill pan made of self-adhered flashing (or formed metal/plastic pan) sloped 1/8 in to the outside with a back dam ≥ ¼ in high to catch overflow; install jamb flashings up the sides lapped over the pan; install head flashing lapped over the WRB; integrate the head with the WRB above with a flap. NEVER seal the bottom of the window flange (water needs to drain).

Why this exists

Pan flashing catches water that gets past the window unit itself (which always leaks eventually) and drains it out to the WRB. The unsealed bottom flange is non-obvious and frequently mis-detailed — sealing it creates a basin that holds water. Architects should reproduce the BASC diagram on the project's window section, not leave it to installer interpretation.

Categories

Source

Solver enforcement

Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.

Related directives

• Continuous load path from roof to foundation · HUD RSDG §2.4
• Residential structural reliability targets 1-in-100 to 1-in-1000 annual probability of failure · HUD RSDG §2.5
• Residential floor live load: 40 psf minimum (30 psf sleeping rooms) · HUD RSDG §3.4
• Wind load design uses ASCE 7 basic wind speed for the locality · HUD RSDG §3.6
• Ground snow load for Virginia: 25 psf eastern, up to 40 psf western mountains · HUD RSDG §3.7