How to Replace a Window

Project details


1 out of 5 Easy Requires a fair amount of carpentry skills and home-remodeling experience; installation is greatly simplified if window is on ground floor and easily accessible from outside


About $500 to $600 for a high-performance 36 x 54-inch wood insert replacement window

Estimated Time

4 to 6 hours to install an average-size window on the ground floor

When Maddy Krauss and her husband, Paul Friedberg, first laid eyes on their 1897 Shingle-style home, they fell in love with its handcrafted turn-of-the-century construction, wide front porch, and massive entry-hall staircase. They were also delighted to find that many of the original architectural details were still intact, including wood paneling, exquisite carvings, stained-glass windows, and an ornate cast-bronze fireplace.

The windows were another story. The originals had been swapped out a decade earlier for low-quality sash kits that were drafty, ugly, and completely inappropriate for the graceful Victorian-era home, This Old House TV's fall 2007 project in Newton, Massachusetts. The solution: Call in TOH general contractor Tom Silva and his crew to install energy-efficient replacements.

Because the existing window frames were sound and square, Tom could use insert replacement units—in this case, Andersen's Woodwright Insert Replacement Windows, vinyl-clad wood units fitted with energy-saving, low-e insulated glass. These fully assembled, ready-to-install windows slip right into the existing openings.

When the job was done, the house had beautiful new double-hungs that looked right, worked smoothly, and gave Maddy and Paul one more thing to love about their old house. Here's a look at how Tom made the switch, with tips for choosing and installing replacement windows.

How to Install Replacement Windows

1. Window Replacement Parts

Illustration by Robert Hardin

Types of Replacement Windows

Unlike full-frame windows, which are designed for new construction, replacement windows are made to fit into existing window openings. They're available in dozens of standard sizes, from as narrow as 11 ½ inches to as wide as 68 inches, and come in wood, vinyl, fiberglass, vinyl-clad wood, and aluminum-clad wood.

There are three basic types of replacement windows: sash kits, insert replacements, and full-frame units. Sash-replacement kits—what Tom found on the Newton house—give an old window frame new movable parts, including jamb liners and sash. The liners are fastened to the side jambs of the window opening, then the sash are slipped in between.

For these to work, the existing window frame must be level and square. An insert replacement window consists of a fully assembled window in a ready-to-install secondary frame. Sometimes called a pocket window, an insert replacement slips into the existing opening and is then fastened to the old side jambs. Because you're adding new jambs and liners, the glass area will be slightly smaller than it was before.

Full-frame replacement windows are similar to inserts, except that they have a complete frame that includes head jamb, side jambs, and sill. These are the only option when the old window frame, sill, or jambs are rotted. To install these, you must strip the window opening down to its rough framing, inside and out.

2. Measuring for Replacements

Photo by Russell Kaye

The most important step in the window-replacement process happens long before installation day. It's when you measure the dimensions of the existing window frame to make sure you order a replacement unit that's the right size. Here's how to do it.

3. Take Out the Sash

Photo by Russell Kaye

4. Pry Off The Jamb Liners

Photo by Russell Kaye

5. Prep the Frame

Photo by Russell Kaye

6. Remove the Old Sash Weights

Photo by Russell Kaye

7. Prep For Insulation

Photo by Russell Kaye

Tom likes polyurethane foam, because it's more effective at blocking air than fiberglass insulation.

8. Spray in the Foam

Photo by Russell Kaye

9. Caulk the Opening

Photo by Russell Kaye

10. Install the Window

Photo by Russell Kaye

11. Fasten It Loosely

Photo by Russell Kaye

12. Shim as Necessary

Photo by Russell Kaye

13. Caulk, Prime and Paint

Photo by Russell Kaye


Tools & Materials

  • Tape measure
  • Hammer
  • Flat pry bar
  • Putty knife
  • Caulk gun
  • Cordless drill/driver
  • Spade bit - 3/8-in.
  • Paint scraper
  • Utility knife
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