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Install a replacement window

If you are experiencing air and water leakage through your windows, condensation is forming and mould is developing on the trim, it’s time to replace your windows. This project explains how to install a new window and how to install door or window trim.

Remove the old window

Depending on the type of window, it may be easier to remove the window either from the inside or the outside.
  • 1.1 - Remove the trim from around the window.
  • 1.2 - Lift out the window panels.
  • 1.3 - Remove the wood shims and screws maintaining the frame.
  • 1.4 - Take off the window frame.
Prepare the window opening by checking the sill and studs

Prepare the opening

  • 2.1 - Remove approximately 9" of the exterior vinyl cladding all around the window.
  • 2.2 - Ensure that all parts are in good condition. Clean all debris from the wood frame.
  • 2.3 - Check the sill: it should slope evenly to the exterior over the entire width of the window. Adjust or replace the sill if necessary.
  • 2.4 - Cover the sill and studs with adhesive waterproof membrane. The self-adhesive membrane should cover the nailing strip for the vinyl cladding.
Position and install the window in the opening

Position and install the window

  • 3.1 - Run a bead of silicone caulk on the sill and around the exterior face of the window at the juncture point of the nailing strip.
  • 3.2 - From the outside, center the window into the opening so that the nailing fin is well-supported.
  • 3.3 - Secure the window with shims from the inside.
  • 3.4 - Measure the window casing diagonally from corner to corner making certain the window is plumb, level and square.
  • 3.5 - Level with shims from the inside if necessary.
  • 3.6 - From the outside, nail the nailing fin around the perimeter; start with the lower corners, then the upper corners, then the center. Check the level regularly.
  • 3.7 - From the inside, secure the window by inserting shims at the bottom of the window and on the sides. Plastic shims are preferable since they don't mildew.
  • 3.8 - Cut the ends of protruding shims.
Insulate around the window with fiberglass insulation

Insulate the window from the inside

  • 4.1 - Lightly pack fiberglass insulation all around the window.
  • 4.2 - Fit a neoprene backer rod around the window.

Pro Tip

The upper adhesive flashing must always overlap the lower flashing to prevent water infiltration.
Waterproof the outside of the window with a self-adhesive membrane

Waterproof the window

  • 5.1 - Cover each side of the window with a self-adhesive membrane. Cover the edges of the frame and ensure the membrane is fully adhered.
  • 5.2 - Install run-off moulding and apply a self-adhesive membrane on top of the winder under the air barrier.
  • 5.3 - Apply sheathing tape on the self-adhesive membrane.
  • 5.4 - Lower the air barrier on top of the window and glue.
  • 5.5 - Glue a supplementary air-barrier on the nailing fin under the window.
Reinstall the exterior mouldings and vinyl cladding around the window

Reinstall the exterior cladding

  • 6.1 - Measure around the window.
  • 6.2 - Cut the moulding for the bottom of the window, adding 2" to the width.
  • 6.3 - Cut a 1" notch on each side of the nailing flange on the part resting on the window sill, leaving the front intact.
  • 6.4 - Nail the moulding under each overhang, leaving an extra 1" on each side.
  • 6.5 - Cut two lengths of J-trim for the sides, 2" longer than the height of the window, and nail.
  • 6.6 - Cut the J-trim for the top, 2" longer than the width of the window. At each end, cut a 1" notch at the bottom of both corners of the J-trim and fold back the strip at a right angle.
  • 6.7 - Make a mitre cut in the part before the J-trim at a 45° angle towards the roof line and nail.
  • 6.8 - Fit the upper moulding strips into the notches of the two lateral mouldings to make a rain water run-off.
  • 6.9 - Apply silicone-based caulk around exterior frame and on nail heads.
  • 6.10 - Reinstall the vinyl cladding.
Install the interior mouldings and trim around the window

Install the interior window trim

Just a few steps are necessary to correctly install door and window trim. Discover trade secrets from the professionals for installing finishing mouldings.
Make sure to consult our project Install door or window trims.
Moulding calculator

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