Window Replacement in 13 Steps – This Old House

Project details



out of


Requires a fair come of carpentry skills and home-remodeling experience ; facility is greatly simplified if window is on grind 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, foremost laid eyes on their 1897 Shingle-style dwelling, they fell in love with its handcraft turn-of-the-century construction, wide front porch, and massive entry-hall stairway. They were besides delighted to find that many of the master architectural details were placid intact, including woodwind paneling, exquisite carvings, stained-glass windows, and an flowery cast-bronze fireplace .
The windows were another fib. The originals had been swapped out a decade earlier for low-quality girdle kits that were drafty, despicable, and wholly inappropriate for the elegant Victorian-era home, This Old House television ‘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 cut-in substitute units—in this case, Andersen ‘s Woodwright Insert Replacement Windows, vinyl-clad wood units fitted with energy-saving, low-e insulate glass. These amply assembled, ready-to-install windows slip right into the existing openings .
When the caper was done, the firm had beautiful new double-hungs that looked correct, worked smoothly, and gave Maddy and Paul one more thing to love about their honest-to-god family. here ‘s a look at how Tom made the interchange, with tips for choosing and installing successor windows .

How to Install Replacement Windows

1. Window Replacement Parts

Window Replacement Parts Diagram

Types of Replacement Windows

Unlike full-frame windows, which are designed for fresh construction, successor windows are made to fit into existing window openings. They ‘re available in dozens of standard sizes, from angstrom specialize as 11 ½ inches to as wide as 68 inches, and come in wood, vinyl, fiberglass, vinyl-clad forest, and aluminum-clad wood .
There are three basic types of surrogate windows : sash kits, slip in replacements, and full-frame units. Sash-replacement kits—what Tom found on the Newton house—give an erstwhile window frame new movable parts, including jamb liners and sash. The liners are fastened to the english jamb of the window open, then the sash are slipped in between .
For these to work, the existing windowpane frame must be level and square. An slip in successor window consists of a amply assembled window in a ready-to-install junior-grade skeleton. sometimes called a pocket windowpane, an slip in replacement slips into the existing open and is then fastened to the erstwhile slope jamb. Because you ‘re adding raw jambs and liners, the glass area will be slightly smaller than it was ahead .
Full-frame replacement windows are alike to inserts, except that they have a dispatch frame of reference that includes promontory jamb, side jamb, and sill. These are the alone option when the old window skeleton, sill, or jambs are rotted. To install these, you must strip the window opening down to its rough frame, inside and out.

2. Measuring for Replacements

Man Measuring Windows For Replacement

The most authoritative tone in the window-replacement process happens long before installation day. It ‘s when you measure the dimensions of the existing window frame to make certain you order a replacement unit of measurement that ‘s the right size. hera ‘s how to do it .

  • Start by measuring the inside width of the old window frame, jamb to jamb, in three places: across the top, middle, and bottom. Write down the smallest of the three measurements.
  • Next, measure the frame’s height from the top of the sill to the underside of the head jamb in three places: at the left jamb, in the middle, and at the right. Again, record the smallest measurement.
  • Check the squareness of the frame by measuring the diagonals from corner to corner. The two dimensions should be the same. If the frame is out of square by 1/4 inch or so, don’t worry; the replacement can be shimmed to fit. Anything more may require adjustments to the frame. If the frame is so out of whack that a square replacement wouldn’t look right, you’ll need a full-frame replacement.
  • Finally, use an angle-measuring tool to determine the slope of the sill; some replacements come with a choice of sill angles.

3. Take Out the Sash

Man Removing Sash To Replace Window

  • The first step is to remove the old sash from the window frame. In most cases, you’ll need to pry off or unscrew the interior wooden stops to remove the lower sash. (If you’re planning to reinstall the stops, do this job carefully; they break easily.)
  • Next, take out the parting beads to free the upper sash. If your windows, like these, were previously fitted with sash-replacement kits, there won’t be any beads. Simply press in on the jamb liners and pull the top of the sash forward.
  • Then pivot one side of the sash upward to free it from the jamb liners.

4. Pry Off The Jamb Liners

Man Prying Off Jamb Liners For Window Replacement

  • If the window frame was fitted with vinyl or aluminum jamb liners, use a flat bar to pry them free. In the case of an original window, remove any remaining wooden stops from the window frame.
  • Leave the interior and exterior casings intact.

5. Prep the Frame

Man Using Flat Bar To Pry Off Jamb Liners

  • Scrape off all loose and blistered paint and patch any holes or cracks with an exterior-grade wood putty, such as the ones from Elmer’s or Minwax.
  • Then sand the jambs smooth, and prime and paint the surfaces.

6. Remove the Old Sash Weights

Man Removes Old Sash Weights Off Window

  • If the original sash weights are still in place, take this opportunity to remove them from their pockets and insulate behind the window frame.
  • Unscrew the access panel on each side jamb and pull out the weights.

7. Prep For Insulation

Man Uses Drill To Prep For Window Replacement Insulation

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

  • Make sure to use only low-pressure, minimally expanding foam intended for windows and doors; anything else will bow the frames and keep the sash from working.
  • First, pull out any existing fiberglass in the weight pockets.
  • Then bore 3/8-inch-diameter holes, one near each end and one in the center, down through the sill and up through the head jamb.

8. Spray in the Foam

Man Sprays Foam Into Drilled Holes For Window Replacement Preparation

  • Shoot the expanding foam into the holes until it begins to ooze out. (Tom is using a commercial system, but you can do the same job with foam from a can, like Dow’s Great Stuff.)
  • Also spray foam into the sash-weight pockets in the side jambs. Allow the excess to harden for at least 6 hours, then break or cut it off flush before replacing the sash-weight pocket panels.

9. Caulk the Opening

Man Caulks Along Windowsill For Window Replacement

  • In preparation for installing the window, apply an elastomeric caulk to the exposed inner face of the exterior casings or to the blind stops on the top and sides of the frame. Also apply two continuous beads of caulk along the windowsill.

10. Install the Window

Man Installs New Window

  • Working from inside the room, set the bottom of the insert replacement onto the sill, then tip it up into the opening. Press the window tight against the exterior casings or blind stops.

11. Fasten It Loosely

Man Drills In Window Replacement

  • Hold the window in place with one 2-inch screw driven loosely through the upper side jamb and into the framing. The screw should be in just far enough to allow the window to operate.
  • Close and lock the sash.

12. Shim as Necessary

Wooden Shim Under Window Sill

  • Adjust the unit by inserting shims under the sill and behind the side jambs until it is centered in the space and opens, closes, and locks smoothly.
  • Measure the window diagonally from corner to corner; the measurements should be the same. When the window is square, screw it in place through the predrilled holes.
  • To avoid bowing the frame, slip a shim behind the jamb at each screw, then screw through the shim.
  • Trim the shims flush with a utility knife.

13. Caulk, Prime and Paint

Man Stands In Front Of Window Replacement To Find Gaps

  • From the outside, measure the gaps between the window frame and the casing. Fill gaps less than 1/4 inch wide with elastomeric caulk. Anything wider must first be stuffed with foam-rubber backer rod.
  • On the inside, fill any gaps around the window with minimally expanding foam.
  • Finish up by reinstalling the stops or adding new ones.
  • Then prime and paint, or stain the interior of the window sash and frame.


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