If you have older wooden windows, you may have noticed drafts leaking around the edges of the moveable sash. This air leakage will cool your house in the winter, heat it up in the summer, and allow dust and debris into your home during windy weather.

Traditional wooden double-hung windows, with an upper and lower sash that slide past one another, are fairly easy to weatherstrip if you’re handy with tools.

Paint is the primary obstacle to weather-stripping windows. The upper sash has often slipped down and is locked in place by layers of paint, making it impossible to seal effectively. Unless the window slides freely and the paint is in good shape, plan on stripping and re-painting the window before weather-stripping.

To weatherstrip double-hung wood windows:

  • Cut the paint seal with a knife around both the upper and lower sash, both inside and outside.
  • Pry off one of the lower sash’s wooden stops–these strips hold the window in place. Be sure to cut a line through the paint where the stop meets the jamb so paint doesn’t pop off as you pry.
  • Remove the lower sash. If it was too tight in the opening, use a plane to remove enough wood so it slides freely.
  • Use a strong board and block, or a small hydraulic jack, to boost the upper sash back to its original position. Be careful to apply pressure only at sash corners so you don’t break the glass.
  • Scrape excess paint from the sashes and windowsill.
  • Apply vinyl V-strip to the side jambs, and bronze or vinyl V-strip to the meeting rail on the top sash. You can get these materials at most hardware stores.
  • Reinstall the lower sash and wooden stops.
  • Your weatherstrip will work better if only the lower window sash needs to slide. Block, screw, or nail the upper sash in place. It will now be immovable, allowing you to effectively weatherstrip the lower sash.

When you repaint the window, don’t paint the weatherstrip or the channels where the sash slides. If the window sticks, lubricate the channels with a bar soap or candle wax.

If your home was built before 1979, your windows may contain lead-based paint. Use polyethylene barriers to contain dust. Wear a respirator and coveralls while working and avoid spreading dust. Clean up with a HEPA vac and mop or wet-wipe all surfaces meticulously.

You can move the top sash up into its original place with a bottle jack, but jack only at the corners of the sash so you don’t break the glass.

For more information about weatherstripping windows, see The Homeowners Handbook to Energy Efficiency.