How to Replace Rotten Window Frames

Written by alex smith
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How to Replace Rotten Window Frames
Rotten window frames can easily be replaced with new trim. (window image by Edvin selimovic from

Wooden window frames are subject to rot and decay as the seasons take their toll. Eventually the damage will be great enough that the frames need to be replaced. If your home has windows that need this type of repair, you may be tempted to hire a contractor. This is often an unnecessary expense, as replacing window frames is not nearly as challenging as you may think, and requires only some basic tools and some new window trim.

Skill level:

Things you need

  • Hammer
  • Pry bar
  • New window trim
  • Measuring tape
  • Mitre saw
  • Drill and bits
  • Finishing nails
  • Putty (optional)
  • Sandpaper (optional)
  • Paint (optional)

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  1. 1

    Check the corners of the old frame to see how they are connected. Most frames use either 45-degree cuts to join the pieces like a picture frame, or 90-degree cuts if the pieces simply butt up against each other.

  2. 2

    Remove the old window frame with a hammer and pry bar. If it is possible to remove the pieces of frame without destroying them, set them aside. Be sure to remove all nails that were holding the old frame in place.

  3. 3

    Measure the new trim to fit in the window. If the pieces of old frame are intact, you can use them as a guide. Otherwise, measure the sides of the window and transfer those measurements to the new trim pieces.

  4. 4

    Cut the new trim pieces with a mitre saw. Follow the angles used in the old frame.

  5. 5

    Position the new trim into the window, holding it in place to ensure that everything fits. Make additional cuts if needed. If there are gaps, you can cut a new piece of trim or use putty to fill the gaps in after the trim is in place.

  6. 6

    Drill pilot holes in the trim to keep the material from splitting.

  7. 7

    Nail the trim in place around the window.

  8. 8

    Fill in any gaps with putty. Allow it to dry, then sand it flush with the rest of the trim.

  9. 9

    Seal the edges of the trim with outdoor caulking and paint if desired.

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