Installing a Wood Window

This story shows you how to install a wood window.


These instructions are for a window with no nailing flange. (If your window has a flange. Most unflanged windows are made of wood, and most have brick molding.

When ordering a window be sure to specify a jamb of the correct width. If your walls have 2x4 studs and 1/2-inch exterior sheathing, the jambs should be 3 5/8 inches wide (the extra 1/8 inch allows for imperfections). For a wall with 2x6 studs, a jamb width of 5 5/8 inches is correct.

Unpack the window and inspect it before installing. Make sure all the weatherstripping is in good shape and the mechanisms and sashes operate smoothly.

Check with your building department to find which method of wrapping the opening is preferred; some departments have stringent requirements.

Prestart Checklist

Once the opening is framed, about 3 hours to seal the opening and install a window and its exterior trim; also allow time for finishing the interior wall and installing interior trim.

Tape measure, hammer, nail set, level, stapler, caulk gun, drill with screwdriver bit, flat pry bar, handsaw, reciprocating saw, tin snips

Careful fitting, driving nails or screws, checking for level and plumb

Frame the opening and check for square.

10d nails or 2-inch deck or wood screws, 8d casing nails, 6d finish nails, wood putty, shims, insulation, exterior caulk, roofing felt or building wrap, staples

Step 1

Cut strips of roofing felt or building wrap and cover the bottom of the rough opening. Later (steps 7-9) you will install additional wrapping and/or flashing.

Step 2

Set the window temporarily in place, check for level, and shim the bottom as needed. If your window calls for installing a thick flashing with a piece of plywood at the bottom install it first or raise the window by the same thickness.

Step 3

Tap in shims at the sides, checking for plumb as you go. Don't wedge the shims too tightly, or the jambs will warp. Use the level as a straightedge to confirm that the jamb has not warped.

Step 4

Make sure the window operates smoothly with the shims in place. Watch the alignment of the sash against the jambs as you move it. Adjust the shims as needed.

Step 5

Tack (partially drive) nails or screws near the shims to hold the window temporarily in place.

Step 6

On the outside, trace around the brick molding to mark the siding for cutting. Cut the siding.

Step 7

Pry back the siding and install the felt, building wrap, or self-adhesive flashing. Cut pieces of felt or self-adhesive flashing to fit along the sides. Slip them in behind the siding, fold them over the studs, and staple. Cut a piece 6 inches longer than the width of the opening and install it the same way. Cut slits at the corners.

Step 8

The slits cut on all four corners create V-shaped openings in the felt or flashing. Cover these with small pieces of felt or self-stick flashing.

Step 9

If your window calls for it, use tin snips to cut a piece of metal drip cap flashing and slip it under the felt at the header.

Step 10

Set the window back in place, with the brick molding tight against the felt or flashing. Inside, the front of the jambs should be flush with the finished wall. (Where you have not yet installed new drywall, the jambs should be 1/2 inch proud of the framing.)

Step 11

Again shim the bottom and sides, check for level and square, and check that the window operates smoothly. Following manufacturer's directions (you may need to remove pieces of trim first), partially drive 6d finishing nails through the jambs to attach the window.

Step 12

Outside, drive galvanized casing nails to attach the brick molding. Caulk between the trim and the window and between the trim and the siding.

Step 13

Use a nail set to drive the finishing nails slightly below the surface of the wood. Where these nails are not covered with trim, apply wood putty to the resulting holes.

Step 14

Use a handsaw to cut the shims flush with the studs, so you can install the drywall up against the jambs.

Step 15

Gently stuff fiberglass insulation into the gaps around the jambs or fill the gaps with nonexpanding spray foam insulation. Expanding foam could warp the window frame.

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