Windows and doors leak, especially at corners, so a sill pan beneath them collects that water and drains it outside. A pan has a back dam to keep water from flowing inward, end dams at the jambs and a front edge that drains over the cladding or WRB below. Pans are preformed metal, plastic, or made from self-adhered membrane with corner pieces.
Every opening gets a sill pan with back dam and end dams before the window goes in. No exceptions.
Sill pan corners are where most window leaks start, so preformed corner pieces or folded dog ears beat cut-and-taped corners.
Also heard as
- pan flashing
- sill flashing
- sub-sill
Related terms
End dam
An upturned end at the termination of a flashing that stops water from running off the end into the wall.
Flashing
Thin sheet metal or membrane installed at joints and interruptions in a wall or roof to direct water back outside.
Dog ear
A corner of flashing or membrane folded into shape without cutting, so the corner stays watertight.
WRB
Water-resistive barrier, the layer behind cladding that sheds water that gets past the outer skin.