Step By Step Guide to Replacing Your Old Windows


If your current windows are broken, building condensation, or drafty, it’s time for a replacement. While most people use a professional installer to replace their windows, it is possible to do the job yourself with a bit of instruction.

Most people are intimidated by home repair projects. However, it’s possible to install new windows in your home in just a few hours with minimal tools. You can save money on your installation costs by tackling this type of project on your own. 

A replacement window fits into an existing window opening, unlike a full-frame window. There are a wide variety of sizes from which to choose. A replacement window can be a sash kit, an insert replacement, or a full-frame unit. 

New movable parts are included in sash-replacement kits, including jamb liners. Window liners are fastened to window opening jambs, and then sashes are slipped in. These require a square and level window frame. 

The insert replacement window is a ready-to-install frame. Insert replacements slip into existing openings and are fastened to side jambs. There will be a slight reduction in glass area due to new jambs and liners.

Replaced full-frame windows have a complete frame, including head, side, and sill jambs. In cases of rotted frames, sills, or jambs, these are the only options. To install this style, you need to strip the opening down to its framing and follow these tips when replacing windows in an old house.

Necessary Tools

Replacing your windows may be intimidating, but it’s easier than you think. Most people have the tools that they need around their house. Everything that you need can be found at your local hardware store. Here is a list of the tools and equipment you will need to tackle this window replacement project:

  • Flat pry bar
  • Tape measure
  • Hammer
  • Bundle of wood shims
  • Caulking gun
  • Putty knife
  • Cordless drill
  • Paint scraper
  • Exterior caulking
  • Wood filler putty
  • Utility knife
  • Can expanding foam insulation


Measuring the existing frame is the most important step. This will give you the interior and exterior measurements of the frame and your needed window sizing. These measurements should be made before you order your new windows.

Measure the interior width of the window frame: across the top, bottom, and middle. Take the smallest measurement. Measure the frame’s height at three points: the left jamb, the right jamb, and the bottom jamb. Take the smallest measurement. From corner to corner, measure the diagonals of the frame. Both dimensions should match. The frame can be shimmed if it is slightly off square. You can make your own wood shims or buy a package of precut wood shims at your local hardware store.  

Remove the Sash

Removing the sash from the frame is the first step. To release the upper sash, remove the parting beads. Pull the sash forward by pressing on the jamb liners. The sash can then be freed from the jamb by pivoting one side upward.

Remove Liners

Use a flat bar to pry the aluminum or vinyl liners free of the frame. Depending on whether it is an original window or not, remove any wooden stops from the frame. Make sure the casings are intact on both the inside and outside. If the casings are rotted, you may need to install an entirely new frame into the place. Rotted liners and frames can indicate a mold or moisture problem that needs to be addressed. 


Prepare Frame

Use exterior wood putty to patch any holes or cracks and remove all loose paint and blisters. Your frame adhesive will not dry firmly unless it is applied to a flat and even surface. After that, sand the jambs smooth and paint or prime them. If you are going to paint your frame prior to adding your new windows, you will need to allow the paint or stain to set and dry thoroughly before continuing with the installation. 

Prepare for Insulation Installation

Fiberglass insulation is less effective at reducing air seepage than polyurethane foam. If you use anything other than minimally expanding foam, the frames will bow, and the sashes will not open. Bore three 3/8-inch holes into the sill and the head jamb, one at each end and center.

Install Installation

The expanding foam needs to be added into the drilled holes to the point where it starts to ooze out. If you have never used expanding foam before, you may want to practice with the trigger a few times before attempting to fill the windows. 

The side jambs also need to be foamed in the pockets for the sash weights. Replace the pocket panels after the excess has hardened for at least six hours. You may need to trim down the excess dried insulation with a saw or knife.


In preparation for installation, the exterior casings and blind stops should be caulked with an elastomeric interior/exterior caulking. Apply one continuous bead of caulking along the window sill as well.

Install Window

Set the bottom of the replacement insert on the sill and tip it up into the opening, working from inside the room. Secure the window to the exterior casing or blind stop using a 2-inch screw.

Secure Window Loosely

Drive a screw into the side jambs to hold the window loosely in place. The sash should be closed and locked.

Shim to Fit

To center your new window, add shims to the underside of the sill, and the side jams. Take a diagonal measurement. The window should be square before being screwed in place. Cleanly trim the shims.


You should measure the gap between the casing and the window frame from the outside. Elastomeric caulk should be used to fill gaps less than a quarter inch in width. Foam-rubber backer rod must be stuffed into anything wider. Minimally expanding foam should be used to fill in any gaps around the window on the inside. Reinstall the stops or add new ones if necessary. Paint or stain the window frames and sashes inside after priming.

If your home is ready for new windows, follow these steps to install new windows in just a few hours. 

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