How to Install Andersen Window Extension Jambs

Andersen windows are available in different styles and sizes, with jambs or frames measuring 4 9/16 inches in width. While these jambs fill window openings in newer homes, they require an extension to fill the depths of the openings in older homes with 2-by-6-inch walls. The extension jambs, or strips of wood, are attached to the inner edges of the jambs to increase jamb depth, so they match the dimensions of the window opening. With a few basic tools, you can easily install an extension jamb to your Andersen window.

Measuring tape
Miter table
Drill and 1/8-inch drill bit
Screwdriver
1 5/8-inch screws

Instructions

- 1
  Measure the lengths of the Andersen window jambs and record the measurement. Transfer the marks on the jambs where you have to make the cuts.
- 2
  Lay the extension jamb under a miter table. Set the blade of the miter saw at 90 degrees and line it up against the mark on the jamb. Turn the saw on and cut straight through the mark. Set this jamb aside and repeat the process for the other jamb.
- 3
  Bore pilot holes into the extension jambs using a drill fitted with a 1/8-inch drill bit, 3 inches from the ends. Space the pilot holes 12 to 16 inches apart along the span of the jambs. Also drill a 3/32-inch hole through the center of the inner edge of the jamb.
- 4
  Place the head extension jamb flush against the top of the Andersen window jamb in the opening. Insert a 1 5/8-inch trim screw into each pre-drilled hole along the span of the extension jamb to secure it in place. Repeat the process to install the side extension jambs the same way, followed by the sill jamb extension. Ensure the extension jambs fall flush against the window jambs, with no gaps in between.
- 5
  Bore pilot holes through the corners of the extension jambs and secure with 1 5/8-inch trim screws.

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