What sill pan flashing means
Sill pan flashing is a formed or taped pan under a window or door opening that catches water that gets past the unit and sends it outside.
Also called pan flashing.
Where it matters on a window and door job
It is the most skipped detail on window and door installs, and the reason for many rotted subfloors. Make it standard and mention it on the estimate as a quality point.
What the model code says
- The code defines pan flashing as corrosion-resistant flashing at the base of an opening, integrated into the wall to direct water to the exterior. (IRC 2021, Chapter 2)
Check which code edition your building department enforces for sill pan flashing before you quote.
What it costs
Jobs that involve sill pan flashing are priced in the window replacement cost guide: about $750 typical, usually $350 to $1,100. The guide shows its sources and what moves the price. The window replacement cost calculator prices a job line by line.
Work it out
- Free calculator: Window replacement cost calculator
- Cost guide: Window replacement cost
- Tools, templates and guides: Free window and door resources
Sources: 2021 International Residential Code, Chapter 2, Definitions (ICC). Checked October 9, 2026.