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Jobsite Test: Is Your New Window Watertight?

April 03, 2017

A simple test to verify that windows are waterproof BEFORE you install them.

"For a long time in my career, I just assumed that the windows that were dropped off and ready to be installed on my jobsite were all waterproof.

But a couple of years ago, I started testing my windows and I was shocked that some of them leaked."

—Matt Risinger

Matt learned this trick from a builder in Seattle, who does large retrofit jobs, often with as many as 200 lower-cost vinyl windows per job. This builder regularly found 20 percent of a large load would leak.


For this jobsite test, Matt chose an inexpensive vinyl window explicitly for its expected vulnerabilities. One of those potential leak spots is the corner.

"Vinyl windows are heat seamed in the corner, so basically, there is a hot plate and they push this miter together and there is some squeeze-out. And that squeeze-out of vinyl gets trimmed.

If the trimming machine is off by a few thousandths, we might have a problem..."

Another possible issue with this window, is the center mull (it is a glider). There is hardware screwed into the mull, which makes Matt " ...a little nervous."


Here's the test:

  • On the outside of the window, cover the weep holes with a little bit of duct tape.
  • Pour water into the window pan.

The idea is that as water is deflected off the window and into the pan it will flow out the weep holes. By sealing the weep holes, you can locate leaks.

This isn't just a parlor trick for jobsites. It is also an ASTM test that window manufacturers are supposed to be able to pass. The test states that the window can't leak with the pan full of water for ten minutes.

Mat uses food coloring to make it easier to spot the leak. Sure enough, the window begins leaking before he has even finished filling the pan with red water.

After ten minutes, the only leak is in the center mull where hardware is fastened. The corner that looked vulnerable remained dry, but he has seen many other corners leak.

"Going back to my builder buddy. he'd get 200 windows, test them all, about 20 percent would leak. He'd send them, back to the factory—these were low-cost vinyl windows—he'd get 40 more back, and again, 20 percent of those would leak."

Bottom line: You can and should check any and all windows before you install them. It is worth doing, especially if you use lower-cost windows.


  • The better the window, the less chance this is going to happen.
  • Over time, though, even the best windows could become leaky from building settling, expansion and contraction, or other issues.
  • Make the window rough opening water proof with peel and stick flashings, interior sealing, and sloped sills.

For more information about choosing and installing windows, Matt has a lot more on his blog.

—Matt Risinger is a custom builder, remodeler, and YouTuber in Austin, Texas

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