How do you fix a leaky window?

A leaky window frame must be repaired immediately

Notice signs

A window frame can either leak immediately after installation or it can leak over time. In most cases, the cause is to be found in the bond between the window frame and the masonry or reveal. While there are construction and assembly defects with new windows, material fatigue or damage can usually be assumed for old windows.

Typical signs of leaky windows are:

  • Crumbling masonry
  • Damp masonry
  • Moisture in the window frame
  • Profile deformations
  • Defective putty
  • Loosening construction foam
  • Eroded window sealing tape

Damage analysis

Before repairing a window, all leaks must be localized. In earlier times, the space between the masonry and the old windows was often only filled with foam. If no additional sealing tape can be seen, it must be attached later. When sealing the window reveal, insulation from the inside is often recommended in order to avoid masonry and plastering work.


The ability to repair a window frame depends heavily on the material. While wooden frames can normally be sealed well even with old windows, a warping of the material can be the cause of leaky plastic windows.

When isolating the window frame, the leaks should be circled, localized and repaired according to the principle of trial and error. A candle and blow dryer can be helpful in tracking it down. It is also important to check the lower reveal and, if necessary, to seal the window sill.

If a window pulls after the window frame has been excluded as the cause, the closing mechanism, the position of the profiles and the glazing including window putty must be checked.

If there are leaky windows in your rented property, this entitles you to a rent reduction. In most cases, five to twenty percent is deemed appropriate by the courts. If moisture enters and causes water and mold damage, up to fifty percent can be reduced.