Leaky window

Let’s first determine what a “leaky window” is. When a window is leaking, you usually see water dripping from top of the window, between the window and drywall or trim. If you see water on the glass, most likely it’s condensation (tips about condensation), and if you see water in between panes (inside Insulated Glass Unit – IGU) that means that your IGU “failed”, and you need to replace it.

This article is about problems with a leaking window/door.

Years 2022/23 brought us a lot of rain. During that time, I had many phone calls regarding leaking windows.

The main cause of the leak is the incorrect prior installation. It’s usually when the window was replaced to retrofit, and the “installer” removed the old frame, which they are not supposed to do for a retrofit. Another common mistake is using the wrong exterior caulking, applying not enough of it or applying it in the wrong way.

The other reason, why the window may leak, is the poor installation of a new construction window. To beat the competition with a lower estimate, some “installers” are doing it in a cheaper, but incorrect way, which will cause a leak in the long run. Namely, if there is a stucco, they cut it around the window, and then they just cover it with 1×4, or fill up the gaps with a new stucco. To do it right, the plasterer needs to break up a larger area, to be able to overlap the new flashing with the old one, that is behind the stucco on the whole wall. Contrary to popular opinion, stucco is permeable and lets some water through. That is why the flashing is needed underneath, so that water seeping through the stucco can run down along the flashing to the ground. If the flashing is not done right, water will eventually get through into the wall. That will cause water damage, dry rot or even bigger problems, that may spread to different areas over time. An overhang above the window may prevent leaks, but at the same time it may just postpone the problem in time. Remember, under California law, contractors are required to provide a 10-year warranty for latent defects! And that’s a period of time in which you can go after the contractor, if any of your windows is leaking. Of course, you can do it only if they are licensed, and when you have a prove that they performed the job and did so incorrectly.

The above dealt with the obvious reasons, and now let’s talk about less clear situations.

Usually, when people see water on a window, they assume that it is the cause of the leak. I have had some cases in the past when the homeowner called a general contractor, who said it is the roof. The roofer said it is a window. And I said it is not a window and they should talk to a general contractor… Often it’s very hard to find the source. I can replace the window with a new one, install flashing and a window correctly, but I cannot guarantee that it will fix the leakage. Water may go through the roof, piping in the wall, vent in the wall, crack in stucco, a wooden trim or another window above, etc.

As a Homeowner you have two options. Either you will find the source yourself, or you will find a patient contractor that will try to do it for you. They would do a hose test for you. If that will not help, they may open some walls or ceiling and hopefully they may find the reason. Remember though that you will have to pay them for their time and work.

I would always recommend a homeowner to do a hose test before calling a contractor, as this will save both parties a lot of time. The best way to do a hose test is to take a water hose and wet specific area for about 15-30 minutes, and then wait another 15-30 minutes and check the place where the leak occurred. If there is no water, just wet the different area and repeat. This test will help you decide what specialty contractor you should call, and it will help him to decide what needs to be done to fix the problem.