Sometimes a double-hung window won’t slide freely simply because it fits too tightly within its tracks.Tightness may be caused by swelling of the wood due to moisture, a build-up of paint, or by long-term settling of the house.

If you have a double-hung window that doesn’t move freely, use a hammer and chisel to pry off the interior stops that form the track, as discussed in Fixing a Double-Hung Window That Falls Shut.

Sand off any bumps or irregular areas and then nail the stops back in place, allowing a slight bit of play by placing a spacer such as a thin piece of cardboard between each stop and sash as you nail.