Chicago Window Expert

Nobody knows more about windows.

  • By Mark Meshulam

    Mark Meshulam is an window consultant and glass consultant. He investigates window and wall leaks and performs window water testing.

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    If your windows leak, you have a problem much greater than the appearance of water when it rains. Water leaks damage your property and can lead to mold, so your quick action to fix this problem will be very important. The problem is that water leaks in buildings is a complicated subject and each leak is unique. You may need an window consultant to assist.

    A few tips to get you started with your window or wall leaks:

    Did you know Chicago Window Expert offers window water leak testing? More info…

    1. Window condensation
    If it leaks when it is not raining, it could be condensation. We have a different article for that. It’s called Window Condensation: Top 10 Fixes

    Windows condensation appears as beads of water on the face of the window, and typically occurs when the temperature suddenly drops.

    Window condensation appears as beads of water on the face of the window, and typically occurs when the temperature suddenly drops.

    2. Window condensation between the panes of glass
    If you see window condensation between the panes of the glass, where the appearance is of fogging glass or a foggy window, you have what is known as insulating glass seal failure. The article about fogging glass can be found here: Insulated Glass Seal Failure.

    Window condensation between panes is seal failure. Foggy windows are caused by failure of the seal around the glass edge

    Window condensation between panes is called "seal failure". Foggy windows are caused by failure of the seal around the glass edge

    3. Bad window sealant (caulk)
    The first thing to look for with any window leak is the condition of the caulk around the outside of the window. If it has cracks or holes, recaulk the window and see what happens in the next rain. If this is your issue, before you caulk, learn more here: Window Sealant Failure

    This is an adhesive caulk failure where the caulk remained adhered to the window but disengaged from the EFIS surround.

    This is an adhesive caulk failure where the caulk remained adhered to the window but disengaged from the EFIS surround.


    This is also an adhesive sealant failure and can result in leaky windows. This time the caulk is sticking to the brick but not to the window.

    This is also an adhesive sealant failure. This time the caulk is sticking to the brick but not to the window.

    4. Leaking walls above windows

    Did you know Chicago Window Expert offers window water leak testing? More info…

    If you see water coming over or through the top of the window, the water may be coming from above the window and through the inside of the wall. You might have leaking walls instead. You must investigate the construction above the window.

    Water stains at top of leaky window

    Water stains at top of window


    Looking up at the outside of this leaky window we see a curved steel lintel which is made in two pieces. The unsealed seam between them can conduct water into the window head, creating the leak.

    Looking up at the outside of this window we see a curved steel lintel which is made in two pieces. The unsealed seam between them can conduct water into the window head and create a leak.


    Sometimes a window leak is not a window leak at all. This crack in a masonry coping brought a lot of water into the building via the leaking walls.

    Sometimes a window leak is not a window leak at all. This crack in a masonry coping brought a lot of water into the building.


    Leaks through roofing can appear as window leaks. If a leak occurs at the top of a window, go up on the roof. You might be surprised at what you find.

    Leaks through roofing can appear as window leaks. If a leak occurs at the top of a window, go up on the roof. You might be surprised at what you find.

    5. Leaks through window frame corners

    If you see water coming through the bottom of the window, look for the sealant that should always be between the sill part of the window frame and the jamb, or side part of the window frame.

    Leak at bottom of leaky window frame corner. The yellow arrow shows where the sill and jamb of the window frame should have been sealed to one another, but were not. The black arrow shows damage to the interior wood molding.

    Leak at bottom of window frame corner. The yellow arrow shows where the sill and jamb of the leaking window should have been sealed to one another, but were not. The black arrow shows damage to the interior wood molding.

    6. Water leak patterns at walls and windows

    If you are in a larger building, the pattern of the water leaks will be a very important diagnostic tool. Map out the leaks on a picture of each side of the building and see if the leaks are clustered near window frame corners or just on walls. Note any similarities between the water leak stains. Observations about the water leak patterns will lead you to the causes.

    Look for water leak patterns. Visual patterns on the outside of the wall may be clues about leaking walls.

    Look for patterns of water leaks. Visual patterns on the outside of the wall may be clues regarding how the water is moving through the wall system.

    7. Multiple causes of water leaks

    Speaking of causes, there will usually be more than one cause for a water leak. When I tell my clients that even simple leaks can have three separate causes, and complex water leaks can have five causes, they tend to look horrified. But it’s true. Leaks tend to congregate. If you positively identify a water path, don’t stop. Keep looking for more causes that might bring water to the same point of water entry that you just investigated or tested.

    8. Monitor results of water leak repairs

    Following any leak repair, monitor the result. You can accelerate the feedback by performing water testing on the repaired area with water spray from a garden hose or spray rack. Wait until the new caulk is dry before doing this.
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    9. Consider using a window consultant and water testing

    Depending upon the problem, window water testing or testing of leaking walls may be needed. Window testing can be as simple as taping the weep holes and filling the sill of a sliding window or door, or as complicated as building a pressure chamber and a spray rack. Experienced judgement of a window consultant should be used in making this decision.

    Window test in progress. This test uses a spray rack but no pressure chamber. The judgement of the window consultant is needed to decide the best window test for the situation

    Window test in progress. This test uses a spray rack but no pressure chamber. The judgement of the window consultant is needed to decide the best window test for the situation

    More resources from Chicago Window Expert about window leaks:
    Wood Window Leaks
    Aluminum Window Leaks
    Curtainwall Leaks
    Window Glazing Leaks
    Window Sealant Failure

    Do your windows leak?

    Fixing leaky windows requires a window consultant guru

    Tracing window leaks requires a window guru

    Read the rest of this entry »

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