Casement Window Installation Instructions

Written by paul massey
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Modern casement windows are designed to give lasting quality, appearance and operation, and are offered in an almost unlimited number of sizes. The proper installation of a standard single residential casement window insures proper functionality and durability, and can be accomplished using the method professional builders follow.

Manufactured casement window units can be heavy and cumbersome to manipulate, and this installation procedure requires the assistance of a helper.

Skill level:

Things you need

  • Tape measure
  • Hammer
  • Framing square
  • Builder's level
  • Handsaw
  • Pry bar
  • 6-inch sisal flashing paper
  • Staple gun or hammer tacker
  • ½-inch plywood
  • Casement window unit
  • Wood shims
  • 16d finish nails
  • 8d box nails

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  1. 1

    Use a builder's level to check that the sill plate and header of the window's rough opening are level, and check with a framing square to make certain the corners of the opening are square to the sill.

  2. 2

    Install 6-inch sisal flashing paper around the exterior perimeter of the window opening. Begin with the sill piece, keeping the top edge of the flashing paper flush with the top of the horizontal 2 x 4 sill and extending past the side of the opening by approximately 6 inches on both sides. Attach to the framing with a staple gun or hammer tacker. Install the side pieces next, extending past the header height by approximately 6 inches and overlapping the horizontal sill piece. Install the top horizontal piece last, extending 6 inches past the opening width and overlapping both side pieces. This flashing paper provides an added measure of waterproofing to the window perimeter.

  3. 3

    Cut two ½-inch plywood blocks 1½ by 3½ inches. Place one block at each side of the opening's sill and nail in place with 8d nails. The window frame rests on these blocks, and an additional block should be added at the centre point of window units over 36 inches wide for added support.

  4. 4

    Insert the window unit into the opening from the exterior, resting the base on the plywood blocks installed in Step 3. While a helper provides support for the window, use a pry bar inserted into the space between the window jamb and the opening's framing to nudge it left or right to where the gap between the framing and the widow unit are equal at both sides. Hold the window unit from the inside while your helper uses 8d nails into the window unit's nailing flange at the lower two corners, then use a level to check that the widow unit's sill is level.

  5. 5

    Use a framing square at the widow unit's corners to verify the unit is square. Use a pry bar at the top corners of the window frame as in Step 4 to shift the frame lightly if the square shows an adjustment is needed. Hold the window unit from the inside while your helper uses 8d nails into the window unit's nailing flange at the upper two corners. Recheck with the framing square that the frame is square.

  6. 6

    Use 8d nails to complete nailing of the nailing flange across the bottom and at both sides of the window.

  7. 7

    Use a tape measure to verify that the gap at the top between the window frame and the header is consistent across the length of the frame. Nail the top flange to the header.

  8. 8

    Insert layered wood shims into the gap at the side of the window frame to fill the gap. Shims should fit snug but not push against the jamb. Nail in place with two 16d finish nails through the inside surface of the window jamb and shims into the wall framing. Repeat at the perimeter gap, evenly spaced at approximately 8 to 10 inches apart or as needed. Use a nailset to set the nail heads ...-inch below the wood surface.

  9. 9

    Use a handsaw to cut the excess shim material that protrudes to flush with the wall framing surface.

  10. 10

    Install the window opener mechanism per the window manufacturer's instructions. Open and close the window vent to full extension to insure proper functioning.

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