How to Replace Old Windows

Using common carpentry tools, you can install a sash kit or window insert from inside your home without destroying the surrounding interior molding or exterior casing. Better yet, you can do it in less than an hour.

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If you have the right tools and tips, installing a window yourself can be an afternoon project. Whether you're replacing a damaged window or just want a new look, we will show you how to get the results you want without calling in help from a professional. Check out our steps below and get started — You'll be surprised with how great it looks!

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Before Starting

Installing a window yourself will only work when the replacement window is the same size and shape as the old one and when the existing window opening is square. To determine whether your window opening is square, measure it diagonally one way (from the upper left corner to the lower right corner) and then the other (from the upper right corner to the lower left corner). If the opening is square, the two measurements will be the same, give or take 1/8 inch. The slightest deviation from square can prevent the sash from closing and the weather stripping from sealing properly. If that happens, you'll be stuck with drafts, condensation, and high utility bills.

What You Need

  • Utility knife
  • Pry bar
  • Pliers
  • Hammer
  • Level
  • Sash replacement window
  • Nails
  • Caulking gun
  • Caulk
  • Wood putty
  • Paintbrush
  • Paint

Step 1: Measure Window

Successful replacements depend on good measurements of the existing opening to find out how big your new window needs to be. Start by measuring between the left and right jambs at the top, middle, and bottom of the window; the shortest of these three measurements is the window width. After that, measure the distance between the head jamb and sill at the far left side, middle, and far right side of the window; the shortest of these three measurements is the window height.

Step 2: Remove Trim and Head Stop

Score the paint where each piece of trim meets the existing window casing. Scoring the seams prevents the wood from splitting when you remove the trim pieces.

Slide a flat pry bar behind the inside stops and remove the pieces.

Next, score head stop and gently pull it loose with pliers. Set aside for later use.

Tip: After removing a stop or other trim pieces, use pliers to pull the nails through the back of the piece. Doing so reduces the odds that the piece will split or fracture.

Step 3: Remove Jamb Liner

Raise the lower sash 6 to 8 inches, then pry back the old jamb liner. Repeat with the upper sash.

Fold the jamb liner at a 90-degree angle underneath the sash. Repeat with the upper sash, folding the jamb liner across the top of the sash.

Step 4: Remove Window

Remove the old sashes and jamb liner as a single unit. Ask a helper for assistance with larger windows. Use proper lifting techniques to avoid back injuries.

Step 5: Insert new Jamb Liner

Install a liner bracket every 4 to 5 inches along each jamb. Make sure each bracket is level before you nail it on.

Attach the jamb liners to the liner brackets. Each liner should pop into place.

Step 6: Install Sashes

Insert the upper sash in the exterior track of the jamb liner. Open and close the sash to make sure it slides smoothly. Insert the lower sash in the interior track and check that it operates.

Step 7: Install Head and Side Stops

Reattach the head stop. Set the nails below the wood surface. Fill the holes with wood putty and touch up with paint.

Reattach the inside stops. Set the nails and fill the holes with wood putty. Caulk the seams and touch up with paint.

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