How to Install Replacement Windows

Step 1 - Remove Old Window

  1. Always wear safety goggles, gloves and face mask during removal and installation of windows.
  2. Carefully remove inside trim, moldings, and/or stops with broad chisel, and save for later use.
  3. Remove old cords and weights (or spring balances) from bottom sash and carefully remove from frame.
  4. Pry out parting stops at top and sides to allow removal of top sash. Be sure not to damage existing stops or openings.
  5. If existing window is fitted with aluminum tracks, remove securing staples, and remove both sashes and tracks.

Step 2 - Clean and Prepare Opening

  1. For Mechanical Windows, Casement Windows, or Slider Windows, install Sill angle on sill 1/8" behind Blindstop. For all Welded Windows, snap angle to bottom of window frame. See figure 1a.
  2. Close and lock window sashes. Set new window in opening to verify all correct measurements. Remove window from opening.
  3. Add a generous amount of caulk to the inside and outside edge of the stool. Also, add caulk to the outside blindstops and along the top of the opening's header.
  4. If needed, place head expander on top of window and caulk along the top surface. A layer of insulation between the head expander and frame may be added if necessary. Expander legs may also be easily trimmed with a utility knife to accommodate various heights.

Step 3 - Install New Lang Exterior Replacement Window

  1. From the interior wall side, set window (be sure sashes are still locked) into openings and butt the exterior window frame up against the opening blindstops. For Mechanical Windows, do not cut black band until window is installed in opening.
  2. Check the window for plumb and level. Add shims where necessary. It is highly recommended that shims be placed at the middle of the frame and at the middle of the top and bottom sashes. (See figure). Also, install shims behind screw holes to prevent screw tightening from warping frame.
  3. Locate the pre-drilled screw holes on the sides of window frame. For Mechanical and Welded series, holes will be located at the top and bottom of both frames sides, under the window stops. (Oversize windows may also have pre-drilled holes in frame top) For sliders, casement, and oversize windows, remove factory installed screw caps from top and sides.
  4. Secure window to opening by installing screws (supplied) through the screw holes into the frame opening. Re-install screw caps.
  5. If installing a head expander raise expander until it is flush with top of opening. Drill pilot holes and secure to frame with small screws at lowest part of expander.
  6. Replace inside stop (moldings) if necessary.
  7. Install insulation around the entire window between the frame and opening. Be careful, installing too much insulation on top and bottom may cause window to bow.
  8. Carefully re-install inside trim.

For more instructions, see our page on measuring a window for replacement.

* Please note every installation is different. These are just basic suggestions and the installation varies per job and based on the installer. Contractors need to check with the town and/or county to make sure they meet codes and requirements versus our suggested install. Lang is not responsible for any such issues whatsoever.