How to Put an Edge Extender on a New Window

Sometimes you cannot find a new window with the exact same dimensions as the old window. This often leaves a gap between the new window's bottom edge and the sill. Edge, or sill, extenders fill this gap and prevent moisture, drafts, bugs and other debris from entering your home. Extenders come in a variety of lengths and colors. Select an extender that is slightly longer than your new window's width and matches its color.

Tape measure
Marker
Tin snips
Level
Silicone caulk
Caulk gun

Instructions

- 1
  Measure the width from the window's outer stops. Stops are the thin strips of wood or vinyl on the window frame's side jambs. Transfer this measurement to the extender and mark the length with a marker.
- 2
  Cut the extender on the mark with tin snips.
- 3
  Hold the extender in front of the gap it will cover. Make a mark on each of the extender's ends where it overlaps the window's sill.
- 4
  Lay the extender on a flat surface. Connect the two marks you made with the edge of the level and draw a straight line along the extender with a marker.
- 5
  Cut the extender along the line with tin snips.
- 6
  Flip the extender face down. Place a tube of silicone caulk in a caulk gun. Run a bead of caulk along the groove along the extender's back side. Fit the extender into the gap.
- 7
  Run a bead of silicone caulk along the space where the extender meets the window sill, stopping about 1/4 inch from either end.
- 8
  Run a bead of caulk up the extender's sides to close the space between the extender and the stops.

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