How to Install a Window Yourself

Installing Window

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Project Overview
  • Working Time: 1 day
  • Total Time: 1 day
  • Skill Level: Intermediate
  • Estimated Cost: $200 to $400

Windows open interior rooms to the outside and bathe your home in natural light. Yet for all of their many benefits, windows come with a fair number of issues when no longer performing at top condition. 

When window repairs and fixes are no longer helping—or when you simply want a style change—it’s time to replace your windows. And when you decide to replace the windows yourself, you’ll get the added benefit of cost savings.

Basics of Windows

Before beginning the project, you should order either new-construction windows with detachable nailing flanges or replacement windows.


Click Play to See Replacement vs. New-Construction Windows Compared

New-Construction Windows

New-construction windows are installed when a house is under initial construction or when the house is undergoing a major renovation that involves opening up and rebuilding exterior walls. 

New-construction windows have a nailing flange (also called nailing fins) on the outside of the window. This flange runs at a 90-degree angle to the window, allowing the window to be nailed against the exterior wall sheathing.

Some new-construction windows have detachable nailing flanges, effectively transforming them into replacement windows. The junction between the flange and the window can be scored with a utility knife, then bent back and forth until it snaps off.


Do not remove the nailing flanges from a new-construction window to convert it to a replacement window unless the manufacturer expressly states that this is allowable.

Replacement Windows

Replacement windows—sometimes called pocket windows or insert windows—are designed to replace new-construction windows. Replacement windows have no nailing flange. This allows the windows to be inserted into a finished (not rough) window opening.

Unlike new-construction windows, which can be found on the shelves of home improvement centers, replacement windows are always a special order product. You may be able to order replacement windows at your local home center. A few online retailers, too, supply replacement windows to homeowners.

Before Getting Started

To order the windows, use the measuring tape to measure the height and width of the inner opening of the window frame. For each direction, you’ll need to make measurements in at least three places, choosing the shortest of these measurements to write down.

  • Height: When measuring the height, open the window sash slightly, then measure from the spot where the sash touches the sill to the top of the window frame. 
  • Width: When measuring width, measure from side to side of the inner window frame. Do not include the stop moulding (the vertical trim that holds the window securely in the frame).


You measure the height of a window and receive three measurements: 25 inches, 25-1/4 inches, and 24-3/4 inches. Choose the shortest measurement, 24-3/4 inches. Use this measurement when ordering the window.

Safety Considerations

Always wear eye protection and gloves when installing replacement windows. Be careful when handling windows while standing on a ladder. Never stand above the rung indicated as the highest rung for standing. Have an assistant help you out, especially when working on a ladder. 

If you need to remove the old window weights, be careful when handling them since some older balance weights were cast from lead. So, handle the lead weights only with gloves. Do not cut or abrade the lead weights. Be sure to dispose of them properly.

What You'll Need

Equipment / Tools

  • Hammer
  • Cordless drill
  • Manual screwdriver
  • Bubble level
  • Utility knife
  • Measuring tape
  • Paint scraper
  • Pry bar
  • Hand saw and miter box
  • Finishing nailer
  • Safety glasses
  • Gloves
  • Painter's tape


  • Replacement window
  • Stop moulding
  • Fiberglass insulation
  • Shims
  • Wood putty


  1. Remove the Stop Moulding

    On the inside of the house, lay the drop cloth in front of the window. Use the utility knife to slice any caulk or paint connecting the stop moulding to the window frame. Gently pry the stop moulding away from the window frame. There is no need to remove the window trim.

  2. Remove the Existing Window

    The lower part of the existing window—the sash—may fall forward, so be ready to hold it in place. With the cordless drill or manual screwdriver, remove any screws securing the rest of the window to the window frame.


    If the window is difficult to remove, you may need to also remove the blind stop moulding, also known as the exterior stop moulding. This moulding is on the exterior of the window and parallels the interior-facing stop moulding.

  3. Remove or Disconnect Window Weights or Balances

    Internal weights connected to ropes and pulley can be disabled by cutting the ropes and letting the weight fall into the inner side pocket of the window frame.

  4. Clean and Repair the Window Opening

    The inner face of the window frame must be smooth to allow insertion of the replacement window. Pull out nails with the claw end of the hammer. Use the paint scraper to scrape away caulk or paint. With holes, tear off fiberglass insulation and insert it into the hole as far as it will go. Fill dips, dents, and small holes with wood putty.

  5. Dry Fit the Replacement Window

    Fit the replacement window in the window opening. Insert the shims below and to the sides of the window to level, plumb, and center the window in the window frame. Note the location of the shims, then remove them and the window.

  6. Install the Replacement Window

    If the dry-fit is satisfactory, permanently attach the replacement window. If you removed the blind moulding, install that piece now. Run a bead of caulk on the interior-facing side of this moulding. Press the window into the window opening and press it into the caulk. Replace the shims. With the cordless drill, run screws through the shims and into the window opening.

  7. Trim Off the Shims

    Snap off the shims at the score point closest to the wall. If the shims do not snap easily, cut them flush to the wall with the hand saw.

  8. Add Insulation

    Stuff fiberglass insulation in large gaps between the window frame and the window opening.

  9. Install the Stop Moulding

    Nail the interior stop moulding into place with the cordless nailer or with a hammer and finishing nails.

  10. Install New Window Trim (Optional)

    If the window trim was damaged when you removed the window, add new window trim to the front of the window, so that the trim covers the gaps between the window and the window opening.

    If there is trim on the outside around the window perimeter, it may work better to remove the trim and window from the outside. Order a new construction window to fit the opening and mount it using the fins. Apply window flashing tape and replace exterior trim pieces.